Predictors of Response to CDK4/6i Retrial After Prior CDK4/6i Failure in ER+ Metastatic Breast Cancer.

After disease progression on endocrine therapy (ET) plus a CDK4/6 inhibitor, there is no standardized sequence for subsequent treatment lines for estrogen receptor positive (ER+) metastatic breast cancer (MBC). CDK4/6i retrial as a treatment strategy is commonplace in modern clinical practice; however, the available prospective data investigating this strategy have had inconclusive results. To frame this data in a real-world context, we performed a retrospective analysis assessing the efficacy of CDK4/6is in 195 patients who had previous exposure to CDK4/6i in a prior treatment line at our institution. Among patients who had stopped a CDK4/6i due to toxicity, CDK4/6i retrial either immediately after with a different CDK4/6i or in a further treatment line with the same initial CDK4/6i was both safe and effective, with a median time to treatment failure (TTF) of 10.1 months (95%CI, 4.8-16.9). For patients whose disease progressed on a prior CDK4/6i, we demonstrated comparable median TTFs for patients rechallenged with the same CDK4/6i (4.3 months, 95%CI 3.2-5.5) and with a different CDK4/6i (4.7 months, 95%CI 3.7-6.0) when compared to the recent PACE, PALMIRA, and MAINTAIN trials. Exploratory genomic analysis suggested that the presence of mutations known to confer CDK4/6i resistance, such as TP53 mutations, CDK4 amplifications, and RB1 or FAT1 loss of function mutations may be molecular biomarkers predictive of CDK4/6i retrial failure.

Current and emerging treatment approaches for hormone receptor-positive/human epidermal growth factor receptor 2-negative metastatic breast cancer.

In the past decade, significant progress was made in treating hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (mBC), but many clinical questions remain. Cyclin-dependent kinase 4/6 inhibitors are now widely used in combination with endocrine therapy (ET) as standard of care, having demonstrated significant progression-free survival versus ET, and also significant overall survival benefits in the metastatic setting. Inhibition of the PI3K/AKT/mTOR intracellular signaling pathway coupled with ET typically follows first-line therapies. Novel endocrine options including oral selective estrogen receptor down-regulators (SERDs) are in late phases of development, with elacestrant being the first oral SERD to be approved for ESR1-mutant mBC. However, endocrine-refractory disease is inevitable in most patients and represents an area of unmet need, with current recommended options offering poor efficacy, undesirable toxicity, and reduced quality of life. Breakthrough advances in the metastatic setting came via the development of antibody-drug conjugates, which have the advantage of delivering cytotoxic payloads to tumor cells with higher tumor selectivity. Trastuzumab deruxtecan offers a novel therapeutic option for patients with HR+/HER2-low mBC and sacituzumab govitecan is a novel therapeutic option for patients with HR+/HER2- mBC, including those with unmet treatment need in the later-line endocrine-refractory setting. Data gaps still exist regarding optimal sequencing of these novel agents; additional studies into mechanisms of resistance in the metastatic setting would provide further insights. Herein, we describe the current treatment options for HR+/HER2- mBC, including the latest practice-impacting data, and provide commentary on future directions.

TROPION-Breast01: Datopotamab deruxtecan vs chemotherapy in pre-treated inoperable or metastatic HR+/HER2- breast cancer.

Improving the prognosis for patients with metastatic HR+/HER2- breast cancer remains an unmet need. Patients with tumors that have progressed on endocrine therapy and/or are not eligible for endocrine therapy had limited treatment options beyond chemotherapy. Antibody-drug conjugates are a novel and promising treatment class in this setting. Datopotamab deruxtecan (Dato-DXd) consists of a TROP2-directed humanized IgG1 monoclonal antibody attached via a serum-stable cleavable linker to a topoisomerase I inhibitor payload. TROPION-Breast01 is an ongoing phase III study that is evaluating the efficacy and safety of Dato-DXd compared with investigator's choice of standard-of-care chemotherapy in patients with inoperable or metastatic HR+/HER2- breast cancer who have received one or two prior lines of systemic chemotherapy in the inoperable or metastatic setting. Clinical Trial Registration: NCT05104866 (ClinicalTrials.gov).

Antibody-drug conjugates are a type of drug with two parts: an antibody that directs the drug to the cancer cells and a cancer-cell killing toxic payload. By binding to cancer cells before releasing the payload, treatment is directed to the site of action so there are fewer side effects in the rest of the body. Datopotamab deruxtecan (Dato-DXd) is an antibody-drug conjugates made up of datopotamab (antibody) and DXd (payload) which are joined together via a stable linker. Datopotamab binds to a protein found on cancer cells called TROP2; it then goes inside and releases the DXd payload to kill the tumor cells. DXd may leak out to surrounding cancer cells and kill those as well. The TROPION-Breast01 study is comparing Dato-DXd with standard-of-care chemotherapy. Around 700 patients will take part, who have: Tumors that cannot be surgically removed. Tumors that are hormone receptor-positive and do not have HER2 overexpression. Had one or two lines of previous chemotherapy (after the tumor could not be surgically removed, or had spread). Had tumor growth despite hormonal therapy or are ineligible for hormonal therapy. Patients who meet the entry criteria will be randomly assigned to a treatment group in equal numbers to either Dato-DXd or an appropriate chemotherapy, out of four options chosen by the treating doctor. At the end of the study, researchers will look at whether the patients who receive Dato-DXd live longer without their breast cancer getting worse, compared with patients who receive chemotherapy. This study is also looking at how the treatment affects patients' quality of life.

Phase Ia/b Study of Giredestrant ± Palbociclib and ± Luteinizing Hormone-Releasing Hormone Agonists in Estrogen Receptor-Positive, HER2-Negative, Locally Advanced/Metastatic Breast Cancer.

PURPOSE: Giredestrant is an investigational next-generation, oral, selective estrogen receptor antagonist and degrader for the treatment of estrogen receptor-positive (ER+) breast cancer. We present the primary analysis results of the phase Ia/b GO39932 study (NCT03332797). PATIENTS AND METHODS: Patients with ER+, HER2-negative locally advanced/metastatic breast cancer previously treated with endocrine therapy received single-agent giredestrant (10, 30, 90, or 250 mg), or giredestrant (100 mg) ± palbociclib 125 mg ± luteinizing hormone-releasing hormone (LHRH) agonist. Detailed cardiovascular assessment was conducted with giredestrant 100 mg. Endpoints included safety (primary), pharmacokinetics, pharmacodynamics, and efficacy. RESULTS: As of January 28, 2021, with 175 patients enrolled, no dose-limiting toxicity was observed, and the MTD was not reached. Adverse events (AE) related to giredestrant occurred in 64.9% and 59.4% of patients in the single-agent ± LHRH agonist and giredestrant + palbociclib ± LHRH agonist cohorts, respectively (giredestrant-only-related grade 3/4 AEs were reported in 4.5% of patients across the single-agent cohorts and 3.1% of those with giredestrant + palbociclib). Dose-dependent asymptomatic bradycardia was observed, but no clinically significant changes in cardiac-related outcomes: heart rate, blood pressure, or exercise duration. Clinical benefit was observed in all cohorts (48.6% of patients in the single-agent cohort and 81.3% in the giredestrant + palbociclib ± LHRH agonist cohort), with no clear dose relationship, including in patients with ESR1-mutated tumors. CONCLUSIONS: Giredestrant was well tolerated and clinically active in patients who progressed on prior endocrine therapy. Results warrant further evaluation of giredestrant in randomized trials in early- and late-stage ER+ breast cancer.

Matching-adjusted indirect comparison of PFS and OS comparing ribociclib plus letrozole versus palbociclib plus letrozole as first-line treatment of HR+/HER2- advanced breast cancer.

Background: Current standard-of-care first-line treatment of patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer (ABC) is cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) + endocrine therapy. In the MONALEESA-2 trial, first-line ribociclib + letrozole demonstrated statistically significant overall survival (OS) benefit versus placebo + letrozole in postmenopausal patients with HR+/HER2- ABC. In the PALOMA-2 trial, first-line palbociclib + letrozole did not show OS benefit versus placebo + letrozole in a similar patient population. Understanding OS outcomes in the respective trials is critical for treatment decisions; however, there are no head-to-head clinical trial data comparing ribociclib and palbociclib. Objectives: To conduct a matching-adjusted indirect comparison (MAIC) to compare progression-free survival (PFS) and OS of first-line ribociclib + letrozole versus palbociclib + letrozole in postmenopausal patients with HR+/HER2- ABC. Design: Letrozole-anchored MAIC using individual patient data from MONALEESA-2 and published summary data from PALOMA-2. Methods: Using individual data, patients from MONALEESA-2 who matched inclusion criteria from PALOMA-2 were selected, and weighting was conducted to ensure baseline characteristics were similar to those in published aggregated data from PALOMA-2. The Bucher method was used to generate corresponding hazard ratios (HRs). Results: The final effective sample size compared n = 150 (ribociclib) and n = 112 (placebo) MONALEESA-2 patients with n = 444 (palbociclib) and n = 222 (placebo) PALOMA-2 patients. After matching and weighting, patient characteristics were well balanced. MAIC analysis showed a numerical PFS benefit [HR, 0.80; 95% confidence interval (CI), 0.58-1.11; p = 0.187] and significant OS benefit (HR, 0.68; 95% CI, 0.48-0.96; p = 0.031) with ribociclib + letrozole versus palbociclib + letrozole. Conclusion: Results of this cross-trial MAIC analysis showed a numerical PFS benefit and significantly greater OS benefit with first-line ribociclib + letrozole versus palbociclib + letrozole. These results support letrozole + ribociclib as the preferred first-line CDK4/6i for postmenopausal patients with HR+/HER2- ABC. Trial registration: NCT01958021; https://www.clinicaltrials.gov/study/NCT01958021 (MONALEESA-2) and NCT01740427; https://clinicaltrials.gov/study/NCT01740427 (PALOMA-2).

Overall survival with sacituzumab govitecan in hormone receptor-positive and human epidermal growth factor receptor 2-negative metastatic breast cancer (TROPiCS-02): a randomised, open-label, multicentre, phase 3 trial.

BACKGROUND: Sacituzumab govitecan demonstrated significant progression-free survival benefit over chemotherapy in the phase 3 TROPiCS-02 trial in patients with pretreated, endocrine-resistant hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+ and HER2-) metastatic breast cancer with limited treatment options. Here, we report the protocol-specified final analysis of overall survival and endpoints by trophoblast cell-surface antigen 2 (Trop-2) expression and other variables. METHODS: In this randomised, open-label, multicentre, phase 3 trial, which took place in 91 centres across North America (the USA and Canada) and Europe (Belgium, France, Germany, Italy, the Netherlands, Spain, and the UK), patients were randomly assigned (1:1) to receive sacituzumab govitecan or chemotherapy (eribulin, vinorelbine, capecitabine, or gemcitabine). Patients had confirmed HR+ and HER2- locally recurrent inoperable or metastatic breast cancer and had received at least one previous endocrine therapy, a taxane, and a CDK4/6 inhibitor in any setting and two to four previous chemotherapy regimens for metastatic disease. The primary endpoint was progression-free survival (previously reported and not included in this analysis), and secondary endpoints included overall survival, objective response rate (ORR), and patient-reported outcomes. Overall survival was assessed using stratified log-rank tests and Cox regression. Trop-2 expression was assessed in tumour tissue by immunohistochemistry. In the statistical testing hierarchy, ORR and patient-reported outcomes were tested sequentially if overall survival was significant. This study is registered with ClinicalTrials.gov, NCT03901339. FINDINGS: At the data cutoff date of July 1, 2022, 543 of 776 screened patients were randomly assigned between May 30, 2019, and April 5, 2021, with 272 patients in the sacituzumab govitecan group and 271 patients in the chemotherapy group. With a 12·5-month (IQR 6·4-18·8) median follow-up, 390 deaths occurred among 543 patients. Overall survival was significantly improved with sacituzumab govitecan versus chemotherapy (median 14·4 months [95% CI 13·0-15·7] vs 11·2 months [10·1-12·7]; hazard ratio [HR] 0·79, 95% CI 0·65-0·96; p=0·020); survival benefit was consistent across Trop-2 expression-level subgroups. ORR was significantly improved with sacituzumab govitecan compared with chemotherapy (57 [21%] patients vs 38 [14%]; odds ratio 1·63 [95% CI 1·03-2·56]; p=0·035), as was time to deterioration of global health status and quality of life (median 4·3 months vs 3·0 months; HR 0·75 [0·61-0·92]; p=0·0059) and fatigue (median 2·2 months vs 1·4 months; HR 0·73 [0·60-0·89]; p=0·0021). The safety profile of sacituzumab govitecan was consistent with previous studies (including the TROPiCS-02 primary analysis and the ASCENT trial). One fatal adverse event (septic shock caused by neutropenic colitis) was determined to be related to sacituzumab govitecan treatment. INTERPRETATION: Sacituzumab govitecan demonstrated statistically significant and clinically meaningful benefit over chemotherapy, with a 3·2-month median overall survival improvement and a manageable safety profile. These data support sacituzumab govitecan as a new treatment option for patients with pretreated, endocrine-resistant HR+ and HER2- metastatic breast cancer. FUNDING: Gilead Sciences.

Molecularly Targeted Therapies for Triple Negative Breast Cancer: History, Advances, and Future Directions.

Triple negative breast cancer (TNBC) remains the subtype with poorest prognosis. Despite the subtype's heterogeneity, there is still a paucity in effective targeted therapeutics that offer both good efficacy and tolerability, and chemotherapy remains the backbone of modern TNBC therapy. In the past few years, immunotherapy as well as novel therapeutic modalities like antibody-drug conjugates (ADCs) have shown clinical benefit and have been FDA approved in various clinical stages of unselected TNBC. However, there has not been similar advancement in molecularly targeted therapies, especially when compared to advancements seen in hormone receptor (HR)-positive or HER2-positive breast cancer. PARP inhibitors have been approved for BRCA-mutated TNBC, but responses are short-lived, and resistance remains a barrier for current treatment. PI3K pathway inhibitors approved in HR+ breast cancer has not worked for TNBC and continue to have significant dose-limiting adverse effects. EGFR inhibition has been thoroughly explored in TNBC, but all trials so far have shown minimal efficacy. Nevertheless, despite these setbacks, current research in targeted therapy for TNBC holds great promise in overcoming the barriers of the past and developing novel therapeutic approaches for the future. In this review, we describe molecular targets both identified and validated in the treatment of TNBC, discuss the historical efforts towards development of targeted agents and current areas of improvement, and address promising advances that have the potential to improve outcomes in this heterogenous and aggressive breast cancer subtype. Immunotherapy, ADCs, and AR targeting will be discussed in separate reviews of this edition.

Novel endocrine therapies: What is next in estrogen receptor positive, HER2 negative breast cancer?

Endocrine therapy (ET) is the cornerstone of management in hormone receptor (HR)+ breast cancer (BC). Indeed, targeting the estrogen receptor (ER) signaling at different levels is a successful strategy, since BC largely relies on the ER signaling as a driver of tumorigenesis and progression. In metastatic BC, progression of disease typically occurs due to either ligand-independent ER signaling, which favors tumor proliferation and survival in the absence of hormonal stimuli, or an ER-independent signaling, which exploits alternative transcription pathways. For instance, estrogen receptor 1 (ESR1) mutations induce constitutive ER activity, in turn upregulating ER-dependent gene transcription and causing resistance to estrogen depleting therapies. The largest unmet need lies after progression on ET + cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors, where fulvestrant alone provides an average 2-3-month PFS. In this context, novel oral selective estrogen receptor degraders (SERDs) and other next-generation ETs are being investigated, both as single agents and in combination with targeted therapies. Elacestrant, the next generation ET in most advanced clinical development and the first to be FDA approved, demonstrated improved outcomes compared to standard ETs in ET pre-treated HR+/HER2- metastatic BC in the phase 3 EMERALD clinical trial. Additionally, other agents are showing promising results in both preclinical and early phase clinical settings. In this review, emerging data related to oral SERDs and other novel ETs in managing HR+/HER2- BC are presented. Major challenges and future perspectives related to the optimal sequence of therapeutic options and the molecular landscape of endocrine resistance are also provided.

Capivasertib in Hormone Receptor-Positive Advanced Breast Cancer.

BACKGROUND: AKT pathway activation is implicated in endocrine-therapy resistance. Data on the efficacy and safety of the AKT inhibitor capivasertib, as an addition to fulvestrant therapy, in patients with hormone receptor-positive advanced breast cancer are limited. METHODS: In a phase 3, randomized, double-blind trial, we enrolled eligible pre-, peri-, and postmenopausal women and men with hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer who had had a relapse or disease progression during or after treatment with an aromatase inhibitor, with or without previous cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor therapy. Patients were randomly assigned in a 1:1 ratio to receive capivasertib plus fulvestrant or placebo plus fulvestrant. The dual primary end point was investigator-assessed progression-free survival assessed both in the overall population and among patients with AKT pathway-altered (PIK3CA, AKT1, or PTEN) tumors. Safety was assessed. RESULTS: Overall, 708 patients underwent randomization; 289 patients (40.8%) had AKT pathway alterations, and 489 (69.1%) had received a CDK4/6 inhibitor previously for advanced breast cancer. In the overall population, the median progression-free survival was 7.2 months in the capivasertib-fulvestrant group, as compared with 3.6 months in the placebo-fulvestrant group (hazard ratio for progression or death, 0.60; 95% confidence interval [CI], 0.51 to 0.71; P<0.001). In the AKT pathway-altered population, the median progression-free survival was 7.3 months in the capivasertib-fulvestrant group, as compared with 3.1 months in the placebo-fulvestrant group (hazard ratio, 0.50; 95% CI, 0.38 to 0.65; P<0.001). The most frequent adverse events of grade 3 or higher in patients receiving capivasertib-fulvestrant were rash (in 12.1% of patients, vs. in 0.3% of those receiving placebo-fulvestrant) and diarrhea (in 9.3% vs. 0.3%). Adverse events leading to discontinuation were reported in 13.0% of the patients receiving capivasertib and in 2.3% of those receiving placebo. CONCLUSIONS: Capivasertib-fulvestrant therapy resulted in significantly longer progression-free survival than treatment with fulvestrant alone among patients with hormone receptor-positive advanced breast cancer whose disease had progressed during or after previous aromatase inhibitor therapy with or without a CDK4/6 inhibitor. (Funded by AstraZeneca and the National Cancer Institute; CAPItello-291 ClinicalTrials.gov number, NCT04305496.).

Quality of life with ribociclib versus abemaciclib as first-line treatment of HR+/HER2- advanced breast cancer: a matching-adjusted indirect comparison.

Background: A cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) + endocrine therapy is recommended as first-line treatment for hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer (ABC). Quality of life (QoL) is an important endpoint that affects treatment decisions. Understanding the relevance of CDK4/6i treatment on QoL is gaining importance given use in earlier treatment lines for ABC and an emerging role in treating early breast cancer in which QoL may be more impactful. In the absence of head-to-head trial data, a matching-adjusted indirect comparison (MAIC) permits comparative efficacy between trials. Objective: In this analysis, patient-reported QoL for MONALEESA-2 [ribociclib + aromatase inhibitor (AI)] and MONARCH 3 (abemaciclib + AI) was compared using MAIC with a focus on individual domains. Design: An anchored MAIC of QoL comparing ribociclib + AI versus abemaciclib + AI was performed using data from the European Organization for Research and Treatment of Cancer quality of life questionnaire (QLQ)-C30 and BR-23 questionnaires. Methods: Individual patient data from MONALEESA-2 and published aggregated data from MONARCH 3 were included in this analysis. Time to sustained deterioration (TTSD) was calculated as the time from randomization to a ⩾10-point deterioration with no later improvement above this threshold. Results: Patients from the ribociclib (n = 205) and placebo (n = 149) arms of MONALEESA-2 were matched with patients from the abemaciclib (n = 328) and placebo (n = 165) arms of MONARCH 3. After weighting, baseline patient characteristics were well balanced. TTSD significantly favored ribociclib versus abemaciclib in appetite loss [hazard ratio (HR), 0.46; 95% confidence interval (CI), 0.27-0.81], diarrhea (HR, 0.42; 95% CI, 0.23-0.79), fatigue (HR, 0.63; 95% CI, 0.41-0.96), and arm symptoms (HR, 0.49; 95% CI, 0.30-0.79). TTSD did not significantly favor abemaciclib compared with ribociclib in any functional or symptom scale of the QLQ-C30 or BR-23 questionnaires. Conclusions: This MAIC indicates that ribociclib + AI is associated with better symptom-related QoL than abemaciclib + AI for postmenopausal patients with HR+/HER2- ABC treated in the first-line setting. Trial registration: NCT01958021 (MONALEESA-2) and NCT02246621 (MONARCH 3).

Antitumour activity of neratinib in patients with HER2-mutant advanced biliary tract cancers.

HER2 mutations are infrequent genomic events in biliary tract cancers (BTCs). Neratinib, an irreversible, pan-HER, oral tyrosine kinase inhibitor, interferes with constitutive receptor kinase activation and has activity in HER2-mutant tumours. SUMMIT is an open-label, single-arm, multi-cohort, phase 2, 'basket' trial of neratinib in patients with solid tumours harbouring oncogenic HER2 somatic mutations (ClinicalTrials.gov: NCT01953926). The primary objective of the BTC cohort, which is now complete, is first objective response rate (ORR) to neratinib 240 mg orally daily. Secondary objectives include confirmed ORR, clinical benefit rate, progression-free survival, duration of response, overall survival, safety and tolerability. Genomic analyses were exploratory. Among 25 treatment-refractory patients (11 cholangiocarcinoma, 10 gallbladder, 4 ampullary cancers), the ORR is 16% (95% CI 4.5-36.1%). The most common HER2 mutations are S310F (n = 11; 48%) and V777L (n = 4; 17%). Outcomes appear worse for ampullary tumours or those with co-occurring oncogenic TP53 and CDKN2A alterations. Loss of amplified HER2 S310F and acquisition of multiple previously undetected oncogenic co-mutations are identified at progression in one responder. Diarrhoea is the most common adverse event, with any-grade diarrhoea in 14 patients (56%). Although neratinib demonstrates antitumour activity in patients with refractory BTC harbouring HER2 mutations, the primary endpoint was not met and combinations may be explored.

The oral selective estrogen receptor degrader GDC-0810 (ARN-810) in postmenopausal women with hormone receptor-positive HER2-negative (HR + /HER2 -) advanced/metastatic breast cancer.

PURPOSE: GDC-0810 (ARN-810) is a novel, non-steroidal, orally bioavailable, selective estrogen receptor degrader (SERD) that potentially inhibits ligand-dependent and ligand-independent estrogen receptor (ER)-mediated signaling. METHODS: A phase Ia/Ib/IIa dose escalation, combination treatment with palbociclib or a luteinizing hormone-releasing hormone, and expansion study determined the safety, pharmacokinetics, and recommended phase 2 dose (RP2D) of GDC-0810 in postmenopausal women with ER + (HER2 -) locally advanced or metastatic breast cancer (MBC). Baseline plasma ctDNA samples were analyzed to determine the ESR1 mutation status. RESULTS: Patients (N = 152) received GDC-0810 100-800 mg once daily (QD) or 300-400 mg twice daily, in dose escalation, expansion, as single agent or combination treatment. Common adverse events regardless of attribution to study drug were diarrhea, nausea, fatigue, vomiting, and constipation. There was one dose-limiting toxicity during dose escalation. The maximum tolerated dose was not reached. GDC-0810 600 mg QD taken with food was the RP2D. Pharmacokinetics were predictable. FES reduction (> 90%) highlighting pharmacodynamic engagement of ER was observed. Outcomes for the overall population and for patients with tumors harboring ESR1 mutations included partial responses (4% overall; 4% ESR1), stable disease (39% overall; 42% ESR1), non-complete response/non-progressive disease (13% overall; 12% ESR1), progressive disease (40% overall; 38% ESR1), and missing/unevaluable (5% overall; 5% ESR1). Clinical benefit (responses or SD, lasting ≥ 24 weeks) was observed in patients in dose escalation (n = 16, 39%) and expansion (n = 24, 22%). CONCLUSION: GDC-0810 was safe and tolerable with preliminary anti-tumor activity in heavily pretreated patients with ER + advanced/MBC, with/without ESR1 mutations, highlighting the potential for oral SERDs. Clinical Trial and registration date April 4, 2013. NCT01823835 .

Sacituzumab Govitecan in Hormone Receptor-Positive/Human Epidermal Growth Factor Receptor 2-Negative Metastatic Breast Cancer.

PURPOSE: Hormone receptor-positive (HR+) human epidermal growth factor receptor 2-negative (HER2-) endocrine-resistant metastatic breast cancer is treated with sequential single-agent chemotherapy with poor outcomes. Sacituzumab govitecan (SG) is a first-in-class antibody-drug conjugate with an SN-38 payload targeting trophoblast cell-surface antigen 2, an epithelial antigen expressed in breast cancer. METHODS: In this global, randomized, phase III study, SG was compared with physician's choice chemotherapy (eribulin, vinorelbine, capecitabine, or gemcitabine) in endocrine-resistant, chemotherapy-treated HR+/HER2- locally recurrent inoperable or metastatic breast cancer. The primary end point was progression-free survival (PFS) by blinded independent central review. RESULTS: Patients were randomly assigned to receive SG (n = 272) or chemotherapy (n = 271). The median age was 56 years, 95% had visceral metastases, and 99% had a prior cyclin-dependent kinase 4/6 inhibitor, with three median lines of chemotherapy for advanced disease. Primary end point was met with a 34% reduction in risk of progression or death (hazard ratio, 0.66 [95% CI, 0.53 to 0.83; P = .0003]). The median PFS was 5.5 months (95% CI, 4.2 to 7.0) with SG and 4.0 months (95% CI, 3.1 to 4.4) with chemotherapy; the PFS at 6 and 12 months was 46% (95% CI, 39 to 53) v 30% (95% CI, 24 to 37) and 21% (95% CI, 15 to 28) v 7% (95% CI, 3 to 14), respectively. Median overall survival (first planned interim analysis) was not yet mature (hazard ratio, 0.84; P = .14). Key grade ≥ 3 treatment-related adverse events (SG v chemotherapy) were neutropenia (51% v 38%) and diarrhea (9% v 1%). CONCLUSION: SG demonstrated statistically significant PFS benefit over chemotherapy, with a manageable safety profile in patients with heavily pretreated, endocrine-resistant HR+/HER2- advanced breast cancer and limited treatment options.

Accelerating drug development in breast cancer: New frontiers for ER inhibition.

The estrogen receptor (ER) is an important driver in the proliferation, tumorigenesis, and progression of breast cancers, and targeting ER signaling at different levels is a successful strategy in the control of hormone receptor positive (HR+) breast cancer. Endocrine therapy has been the treatment of choice for HR+ breast cancer in the early and advanced stages with multiple agents, including selective estrogen receptor modulators (SERMS), selective estrogen receptor degraders (SERDs), and aromatase inhibitors (AIs), which vary in their mechanisms of action and pharmacokinetics. Combination strategies also employ cyclin dependent kinase 4 and 6 and phosphatidylinositol 3-kinase to maximize the benefits of endocrine therapy. This paper reviews the clinical development of SERDs and other novel ER inhibitors, as well as combination strategies to overcome mechanisms of ER pathway escape. It also assesses the advantages of newer oral ER inhibitors with increased bioavailability, improved therapeutic index, better administration, and increased efficacy, as well as discussing future directions in the field.

The Oncogenic PI3K-Induced Transcriptomic Landscape Reveals Key Functions in Splicing and Gene Expression Regulation.

The phosphoinositide 3-kinase (PI3K) pathway regulates proliferation, survival, and metabolism and is frequently activated across human cancers. A comprehensive elucidation of how this signaling pathway controls transcriptional and cotranscriptional processes could provide new insights into the key functions of PI3K signaling in cancer. Here, we undertook a transcriptomic approach to investigate genome-wide gene expression and transcription factor activity changes, as well as splicing and isoform usage dynamics, downstream of PI3K. These analyses uncovered widespread alternatively spliced isoforms linked to proliferation, metabolism, and splicing in PIK3CA-mutant cells, which were reversed by inhibition of PI3Kα. Analysis of paired tumor biopsies from patients with PIK3CA-mutated breast cancer undergoing treatment with PI3Kα inhibitors identified widespread splicing alterations that affect specific isoforms in common with the preclinical models, and these alterations, namely PTK2/FRNK and AFMID isoforms, were validated as functional drivers of cancer cell growth or migration. Mechanistically, isoform-specific splicing factors mediated PI3K-dependent RNA splicing. Treatment with splicing inhibitors rendered breast cancer cells more sensitive to the PI3Kα inhibitor alpelisib, resulting in greater growth inhibition than alpelisib alone. This study provides the first comprehensive analysis of widespread splicing alterations driven by oncogenic PI3K in breast cancer. The atlas of PI3K-mediated splicing programs establishes a key role for the PI3K pathway in regulating splicing, opening new avenues for exploiting PI3K signaling as a therapeutic vulnerability in breast cancer. SIGNIFICANCE: Transcriptomic analysis reveals a key role for the PI3K pathway in regulating RNA splicing, uncovering new mechanisms by which PI3K regulates proliferation and metabolism in breast cancer. See related commentary by Claridge and Hopkins, p. 2216.

Biomarkers for Adjuvant Endocrine and Chemotherapy in Early-Stage Breast Cancer: ASCO Guideline Update.

PURPOSE: To update recommendations on appropriate use of breast cancer biomarker assay results to guide adjuvant endocrine and chemotherapy decisions in early-stage breast cancer. METHODS: An updated literature search identified randomized clinical trials and prospective-retrospective studies published from January 2016 to October 2021. Outcomes of interest included overall survival and disease-free or recurrence-free survival. Expert Panel members used informal consensus to develop evidence-based recommendations. RESULTS: The search identified 24 studies informing the evidence base. RECOMMENDATIONS: Clinicians may use Oncotype DX, MammaPrint, Breast Cancer Index (BCI), and EndoPredict to guide adjuvant endocrine and chemotherapy in patients who are postmenopausal or age > 50 years with early-stage estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative (ER+ and HER2-) breast cancer that is node-negative or with 1-3 positive nodes. Prosigna and BCI may be used in postmenopausal patients with node-negative ER+ and HER2- breast cancer. In premenopausal patients, clinicians may use Oncotype in patients with node-negative ER+ and HER2- breast cancer. Current data suggest that premenopausal patients with 1-3 positive nodes benefit from chemotherapy regardless of genomic assay result. There are no data on use of genomic tests to guide adjuvant chemotherapy in patients with ≥ 4 positive nodes. Ki67 combined with other parameters or immunohistochemistry 4 score may be used in postmenopausal patients without access to genomic tests to guide adjuvant therapy decisions. BCI may be offered to patients with 0-3 positive nodes who received 5 years of endocrine therapy without evidence of recurrence to guide decisions about extended endocrine therapy. None of the assays are recommended for treatment guidance in individuals with HER2-positive or triple-negative breast cancer. Treatment decisions should also consider disease stage, comorbidities, and patient preferences.Additional information is available at www.asco.org/breast-cancer-guidelines.

Characterization, management, and risk factors of hyperglycemia during PI3K or AKT inhibitor treatment.

PURPOSE: The phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) pathway controls insulin sensitivity and glucose metabolism. Hyperglycemia is one of the most common on-target adverse effects (AEs) of PI3K/AKT inhibitors. As several PI3K and AKT inhibitors are approved by the United States Food and Drug Administration or are being studied in clinical trials, characterizing this AE and developing a management strategy is essential. METHODS: Patients with hematologic or solid malignancies treated at Memorial Sloan Kettering Cancer Center with a PI3K or AKT inhibitor were included in this retrospective analysis. A search for patients experiencing hyperglycemia was performed. The frequency, management interventions and outcomes were characterized. RESULTS: Four hundred and ninety-one patients with 10 unique cancer types who received a PI3K or AKT inhibitor were included. Twelve percent of patients required a dose interruption, 6% of patients required a dose reduction and 2% of patients were hospitalized to manage hyperglycemia. No events occurred among patients receiving ß-, γ-, or δ- specific PI3K inhibitor. There was one case where the PI3K or AKT inhibitor was permanently discontinued due to hyperglycemia. Metformin was the most commonly used antidiabetic medication, followed by insulin, sodium-glucose transport protein 2 (SGLT2) inhibitors, and sulfonylurea. SGLT2 inhibitors were associated with the greatest reductions in blood sugar, followed by metformin. At least one case of euglycemic diabetic ketoacidosis (DKA) occurred in a patient on PI3K inhibitor and SGLT2 inhibitor. Body mass index ≥ 25 and HbA1c  ≥ 5.7 are were independently significant predictors of developing hyperglycemia. CONCLUSION: Hyperglycemia is one of the major on-target side effects of PI3K and AKT inhibitors. It is manageable with antidiabetic medications, treatment interruption and/or dose modification. We summarize pharmacological interventions that may be considered for PI3K/AKT inhibitor induced hyperglycemia. SGLT2-inhibitor may be a particularly effective second-line option after metformin but there is a low risk of euglycemic DKA, which can be deadly. To our knowledge, our report is the largest study of hyperglycemia in patients receiving PI3K/AKT inhibitors.

Serial monitoring of genomic alterations in circulating tumor cells of ER-positive/HER2-negative advanced breast cancer: feasibility of precision oncology biomarker detection.

Nearly all estrogen receptor (ER)-positive (POS) metastatic breast cancers become refractory to endocrine (ET) and other therapies, leading to lethal disease presumably due to evolving genomic alterations. Timely monitoring of the molecular events associated with response/progression by serial tissue biopsies is logistically difficult. Use of liquid biopsies, including circulating tumor cells (CTC) and circulating tumor DNA (ctDNA), might provide highly informative, yet easily obtainable, evidence for better precision oncology care. Although ctDNA profiling has been well investigated, the CTC precision oncology genomic landscape and the advantages it may offer over ctDNA in ER-POS breast cancer remain largely unexplored. Whole-blood (WB) specimens were collected at serial time points from patients with advanced ER-POS/HER2-negative (NEG) advanced breast cancer in a phase I trial of AZD9496, an oral selective ER degrader (SERD) ET. Individual CTC were isolated from WB using tandem CellSearch® /DEPArray™ technologies and genomically profiled by targeted single-cell DNA next-generation sequencing (scNGS). High-quality CTC (n = 123) from 12 patients profiled by scNGS showed 100% concordance with ctDNA detection of driver estrogen receptor α (ESR1) mutations. We developed a novel CTC-based framework for precision medicine actionability reporting (MI-CTCseq) that incorporates novel features, such as clonal predominance and zygosity of targetable alterations, both unambiguously identifiable in CTC compared to ctDNA. Thus, we nominated opportunities for targeted therapies in 73% of patients, directed at alterations in phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA), fibroblast growth factor receptor 2 (FGFR2), and KIT proto-oncogene, receptor tyrosine kinase (KIT). Intrapatient, inter-CTC genomic heterogeneity was observed, at times between time points, in subclonal alterations. Our analysis suggests that serial monitoring of the CTC genome is feasible and should enable real-time tracking of tumor evolution during progression, permitting more combination precision medicine interventions.

Clinical and Morphologic Characteristics of Fibroblast Growth Factor Receptor Inhibitor-Associated Retinopathy.

IMPORTANCE: Fibroblast growth factor receptor (FGFR) 1 to 4 inhibitors are approved by the US Food and Drug Administration and suppress the mitogen-activated protein kinase (MAPK) pathway, with a potential for treatment-related retinopathy. To date, implications of FGFR inhibitor-associated ocular toxic effects are poorly described. Therefore, more detailed clinical descriptions of this ocular toxic effect could help explain visual symptoms while receiving drug therapy. OBJECTIVE: To describe the clinical and morphologic characteristics of serous retinal disturbances associated with FGFR inhibitors. DESIGN, SETTING, AND PARTICIPANTS: In this retrospective case series, 146 patients receiving FGFR inhibitors as cancer treatment at a single tertiary referral center were included. This study included 40 eyes of 20 patients with retinopathy by optical coherence tomography (OCT). OCTs were obtained on the remaining patients and the results were judged normal. Patients were recruited from March 2012 to January 2021. MAIN OUTCOMES AND MEASURES: Characteristics of treatment-emergent choroidal and retinal OCT abnormalities as compared with baseline OCT, associated with visual acuity at presentation and at fluid resolution. RESULTS: A total of 20 of 146 patients (13.7%) exhibited FGFR inhibitor-associated retinopathy. Of these 20 patients, 11 (55%) were female, and the median (range) age was 62.6 (42.7-86.0) years. The median (range; mean) time from medication start to initial subretinal fluid detection was 21 (5-125; 32) days. The median (interquartile range [IQR]) baseline logMAR best-corrected visual acuity (BCVA) was 0 (0-0.1). At fluid accumulation, 11 eyes had decreased vision: the median (IQR) subgroup baseline BCVA was 0 (0-0.1); and the median (IQR) BCVA change from baseline to accumulation was -0.1 (-0.2 to -0.1). For 26 eyes (65%) with follow-up, the subretinal fluid resolved without medical intervention or drug interruption in all but 1 patient. At fluid resolution, the median (IQR) BCVA was 0.1 (0-0.1), and the change in median (IQR) BCVA from baseline to fluid resolution was 0 (-0.03 to 0). No patient discontinued drug therapy on account of their retinopathy. CONCLUSIONS AND RELEVANCE: FGFR inhibitors result in subretinal fluid foci similar to other drugs that inhibit the MAPK pathway. In this series, FGFR inhibitors did not cause irreversible loss of vision; the retinopathy was self-limited and did not require medical intervention. These results may explain visual symptoms while taking the drug, although the precise frequency or magnitude of this adverse effect cannot be determined with certainty from this retrospective investigation.

A Phase I Study of LSZ102, an Oral Selective Estrogen Receptor Degrader, with or without Ribociclib or Alpelisib, in Patients with Estrogen Receptor-Positive Breast Cancer.

PURPOSE: Data are sparse for oral selective estrogen receptor (ER) degraders (SERD) in cancer treatment. The investigational oral SERD LSZ102 was assessed in monotherapy and combination use in a phase I study. PATIENTS AND METHODS: A phase I, multicenter, open-label dose-escalation study (NCT02734615) of LSZ102 alone (arm A; n = 77) or with ribociclib (arm B; n = 78) or alpelisib (arm C; n = 43) in heavily pretreated adults with histologically confirmed ER-positive breast cancer and prior disease progression. Arm A received LSZ102 200-900 mg/day; arm B, LSZ102 200-600 mg/day plus ribociclib 300-600 mg/day; arm C, LSZ102 300-450 mg/day plus alpelisib 200-300 mg/day. Key outcomes were dose-limiting toxicities (DLT) in the first 28-day treatment cycle, adverse events (AE), laboratory parameters, pharmacokinetics, biopsy ER protein, and investigator-assessed clinical response (RECIST v1.1). RESULTS: The most common AEs were gastrointestinal. Treatment-related serious AEs occurred in 10% of participants (19/198), mostly in arm C [10/43 (23%)]. DLTs occurred in: arm A, 5% (4/77); arm B, 3% (2/78); and arm C, 19% (8/43). LSZ102 exposure was slightly greater than dose proportional. On-treatment biopsy ER reductions were observed, with a trend toward an LSZ102 dose response. Objective response rates (95% confidence interval) were: arm A, 1.3% (0.0-7.0); arm B, 16.9% (9.3-27.1); and arm C, 7.0% (1.5-19.1), and clinical benefit rates 7.8% (2.9-16.2), 35.1% (24.5-46.8), and 20.9% (10.0-36.0), respectively. CONCLUSIONS: LSZ102 was well tolerated alone and with ribociclib and had a manageable safety profile with alpelisib. Preliminary clinical activity was observed in combination use.