Genomic spectrum of actionable alterations in serial cell free DNA (cfDNA) analysis of patients with metastatic breast cancer.

We aimed to study the incidence and genomic spectrum of actionable alterations (AA) detected in serial cfDNA collections from patients with metastatic breast cancer (MBC). Patients with MBC who underwent plasma-based cfDNA testing (Guardant360®) between 2015 and 2021 at an academic institution were included. For patients with serial draws, new pathogenic alterations in each draw were classified as actionable alterations (AA) if they met ESCAT I or II criteria of the ESMO Scale for Clinical Actionability of Molecular Targets (ESCAT). A total of 344 patients with hormone receptor-positive (HR+)/HER2-negative (HER2-) MBC, 95 patients with triple-negative (TN) MBC and 42 patients with HER2-positive (HER2 + ) MBC had a baseline (BL) cfDNA draw. Of these, 139 HR+/HER2-, 33 TN and 13 HER2+ patients underwent subsequent cfDNA draws. In the HR+/HER2- cohort, the proportion of patients with new AA decreased from 63% at BL to 27-33% in the 2nd-4th draws (p < 0.0001). While some of the new AA in subsequent draws from patients with HR+/HER2- MBC were new actionable variants in the same genes that were known to be altered in previous draws, 10-24% of patients had new AA in previously unaltered genes. The incidence of new AA also decreased with subsequent draws in the TN and HER2+ cohorts (TN: 25% to 0-9%, HER2 + : 38% to 14-15%). While the incidence of new AA in serial cfDNA decreased with subsequent draws across all MBC subtypes, new alterations with a potential impact on treatment selection continued to emerge, particularly for patients with HR+/HER2- MBC.

Selection of appropriate biomarkers to monitor effectiveness of ovarian function suppression in pre-menopausal patients with ER+ breast cancer.

Use of gonadotropin-releasing hormone (GnRH) agonists has been widely adopted to provide reversible ovarian function suppression for pre-menopausal breast cancer patients who are also receiving aromatase inhibitor or tamoxifen therapy based on results of 25 randomized trials representing almost 15,000 women demonstrating a survival benefit with this approach. Past clinical trials designed to establish the efficacy of GnRH agonists have monitored testosterone in the prostate cancer setting and estradiol in the breast cancer setting. We explore the merits of various biomarkers including estradiol, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) and their utility for informing GnRH agonist treatment decisions in breast cancer. Estradiol remains our biomarker of choice in ensuring adequate ovarian function suppression with GnRH agonist therapy among pre-menopausal women with breast cancer. We recommend future trials to continue to focus on estradiol levels as the primary endpoint, as they have in the past.

Glutaminase (GLS1) gene expression in primary breast cancer.

BACKGROUND: Tumor growth is mediated in part by glutamine, and glutaminase is an enzyme necessary for glutamine catabolism. We studied glutaminase (GLS1) gene expression in primary breast cancer to determine correlations with clinical and tumor characteristics, and gene associations in publicly available databases. A better understanding of glutaminase gene expression may help guide further exploration of glutaminase inhibitors in breast cancer. METHODS: GLS1 mRNA levels were evaluated in The Cancer Genome Atlas (n = 817) and METABRIC (n = 1992) datasets. Associations between GLS1 and tumor subtype (ANOVA followed by post-hoc Tukey test for pairwise comparisons) and selected genes involved in the pathogenesis of breast cancer (Pearson's correlations) were determined in both datasets. In METABRIC, associations with overall survival (Cox proportional hazard model) were determined. For all analyses, p < 0.05 was the threshold for statistical significance. RESULTS: GLS1 expression was significantly higher in triple negative breast cancer (TNBC) than hormone receptor (HR) +/HER2- and HER2+ breast cancer (p < 0.001) and basal versus luminal A, luminal B, and HER2 enriched breast cancer (p < 0.001) in both datasets. In METABRIC, higher GLS1 expression was associated with improved overall survival (HR 0.91, 95% CI: 0.85-0.97, p = 0.005) and this association remained significant in the TNBC subset (HR 0.83, 95% CI: 0.71-0.98, p = 0.032). GLS1 had significant positive gene correlations with immune, proliferative, and basal genes, and inverse correlations with luminal genes and genes involved in metabolism. CONCLUSION: GLS1 expression is highest in TNBC and basal breast cancer, supporting ongoing clinical investigation of GLS1 inhibition in TNBC. GLS1 may have prognostic implications but further research is needed to validate this finding. GLS1 had significant positive gene correlations with immune genes, which may have implications for potential combinations of glutaminase inhibition and immunotherapy.

Utilizing cell-free DNA to predict risk of developing brain metastases in patients with metastatic breast cancer.

We compared cell-free DNA (cfDNA) results at MBC diagnosis in patients who developed brain metastases (BM) vs those without (non-BM) to understand genomic predictors of BM. Patients with cfDNA testing at MBC diagnosis (Guardant360®, 73 gene next generation sequencing) were identified. Clinical and genomic features of BM and non-BM were compared (Pearson's/Wilcoxon rank sum tests). Eighteen of 86 patients (21%) with cfDNA at MBC diagnosis developed BM. Comparing BM vs non-BM, a higher prevalence of BRCA2 (22% vs 4.4%, p = 0.01), APC (11% vs 0%, p = 0.005), CDKN2A (11% vs 1.5%, p = 0.05), and SMAD4 (11% vs 1.5%, p = 0.05) was observed. Seven of 18 BM had ≥1 of the following 4 mutations in baseline cfDNA: APC, BRCA2, CDKN2A or SMAD4 vs 5/68 non-BM (p = 0.001). Absence of this genomic pattern had a high negative predictive value (85%) and specificity (93%) in excluding BM development. Baseline genomic profile varies in MBC that develops BM.

Arrhythmogenic Cardiotoxicity Associated With Contemporary Treatments of Lymphoproliferative Disorders.

Background There are limited data on risk of arrhythmias among patients with lymphoproliferative disorders. We designed this study to determine the risk of atrial and ventricular arrhythmia during treatment of lymphoma in a real-world setting. Methods and Results The study population comprised 2064 patients included in the University of Rochester Medical Center Lymphoma Database from January 2013 to August 2019. Cardiac arrhythmias-atrial fibrillation/flutter, supraventricular tachycardia, ventricular arrhythmia, and bradyarrhythmia-were identified using International Classification of Diseases, Tenth Revision (ICD-10) codes. Multivariate Cox regression analysis was used to assess the risk of arrhythmic events with treatments categorized as Bruton tyrosine kinase inhibitor (BTKi), mainly ibrutinib/non-BTKi treatment versus no treatment. Median age was 64 (54-72) years, and 42% were women. The overall rate of any arrhythmia at 5 years following the initiation of BTKi was (61%) compared with (18%) without treatment. Atrial fibrillation/flutter was the most common type of arrhythmia accounting for 41%. Multivariate analysis showed that BTKi treatment was associated with a 4.3-fold (P<0.001) increased risk for arrhythmic event (P<0.001) compared with no treatment, whereas non-BTKi treatment was associated with a 2-fold (P<0.001) risk increase. Among subgroups, patients without a history of prior arrhythmia exhibited a pronounced increase in the risk for the development of arrhythmogenic cardiotoxicity (3.2-fold; P<0.001). Conclusions Our study identifies a high burden of arrhythmic events after initiation of treatment, which is most pronounced among patients treated with the BTKi ibrutinib. Patients undergoing treatments for lymphoma may benefit from prospective focused cardiovascular monitoring prior, during, and after treatment regardless of arrhythmia history.

Detection of microsatellite instability high (MSI-H) status by targeted plasma-based genotyping in metastatic breast cancer.

We evaluate microsatellite instability-high (MSI-H) status with cell-free DNA (cfDNA) in metastatic breast cancer (MBC) and the association with clinico-genomic characteristics. Patients with MSI-H in cfDNA (Guardant360®, 74 gene next-generation sequencing (NGS) with MBC are identified. We conduct a retrospective review. The median number of alterations and a median maximum mutant allelic fraction (MAF) in MSI-H and non-MSI-H cohorts are compared with Mann-Whitney U-test. Of 6718 patients with breast cancer with ≥1 plasma NGS alteration, 42 (0.63%) have MSI-H. A median number of genomic alterations per sample is 11 in MSI-H vs. 3 in non-MSI-H (Mann-Whitney U-test p < 0.0001) and the median maximum MAF is 16.8% in MSI-H vs. 2.6% in non-MSI-H (Mann-Whitney U-test p < 0.0001). The co-existing genomic landscape is heterogeneous. The median response duration for seven patients receiving immunotherapy is 92 days (range 29-273 days). CfDNA can identify MSI-H in MBC. Research is needed to validate immunotherapy usage in cfDNA-detected MSI-H MBC.

Immunogenicity of SARS-CoV-2 vaccines in patients with breast cancer.

Purpose: To explore the immunogenicity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines in patients with breast cancer based on type of anticancer treatment. Methods: Patients with breast cancer had anti-spike antibody concentrations measured ⩾14 days after receiving a full SARS-CoV-2 vaccination series. The primary endpoint was IgA/G/M anti-spike antibody concentration. Multiple regression analysis was used to analyze log10-transformed antibody titer concentrations. Results: Between 29 April and 20 July 2021, 233 patients with breast cancer were enrolled, of whom 212 were eligible for the current analysis. Patients who received mRNA-1273 (Moderna) had the highest antibody concentrations [geometric mean concentration (GMC) in log10: 3.0 U/mL], compared to patients who received BNT162b2 (Pfizer) (GMC: 2.6 U/mL) (multiple regression adjusted p = 0.013) and Ad26.COV2.S (Johnson & Johnson/Janssen) (GMC: 2.6 U/mL) (p = 0.071). Patients receiving cytotoxic therapy had a significantly lower antibody titer GMC (2.5 U/mL) compared to patients on no therapy or endocrine therapy alone (3.0 U/mL) (p = 0.005). Patients on targeted therapies (GMC: 2.7 U/mL) also had a numerically lower GMC compared to patients not receiving therapy/on endocrine therapy alone, although this result was not significant (p = 0.364). Among patients who received an additional dose of vaccine (n = 31), 28 demonstrated an increased antibody response that ranged from 0.2 to >4.4 U/ mL. Conclusion: Most patients with breast cancer generate detectable anti-spike antibodies following SARS-CoV-2 vaccination, though systemic treatments and vaccine type impact level of response. Further studies are needed to better understand the clinical implications of different antibody levels, the effectiveness of additional SARS-CoV-2 vaccine doses, and the risk of breakthrough infections among patients with breast cancer.

Trophoblast Cell Surface Antigen 2 gene (TACSTD2) expression in primary breast cancer.

PURPOSE: Trophoblast Cell Surface Antigen 2 (TROP2) is a glycoprotein expressed in many cancers. A TROP2 antibody-drug conjugate (ADC) was effective in metastatic triple-negative breast cancer (TNBC). We studied TROP2 gene (TACSTD2) expression and associations with tumor and clinical characteristics, as well as selected external genes in primary breast cancer. METHODS: TACSTD2 gene expression was evaluated using microarray data from I-SPY 1 (n = 149), METABRIC (n = 1992), and TCGA (n = 817). Associations with clinical features (Kruskal-Wallis test, all datasets), chemotherapy response (Wilcoxon rank sum test, I-SPY 1), recurrence free survival (Cox proportional hazard model, I-SPY 1 and METABRIC), and selected genes (Pearson correlations, all datasets) were determined. RESULTS: TACSTD2 gene expression was detectable in all breast cancer subtypes, with a wide range of expression (all datasets). TACSTD2 gene expression was lower in HER2 + than HR + /HER2- and TNBC (METABRIC: p = 0.03, TCGA p = 0.007), and in HER2 + enriched and luminal B breast cancer (METABRIC: p < 0.001, TCGA: p < 0.001). TACSTD2 expression was higher in grade I vs. II/III tumors (METABRIC: p < 0.001). No association with chemotherapy response (I-SPY 1) or recurrence free survival (I-SPY 1 and METABRIC) was seen. TACSTD2 has significant positive correlations with the expression of epithelial/adhesion genes and proliferative genes, but was inversely correlated with immune genes. CONCLUSION: TACSTD2 gene expression was seen in all breast cancer subtypes particularly luminal A and TNBC, and correlated with the expression of genes involved in cell epithelial transformation, adhesion, and proliferation, which contribute to tumor growth. These results support the investigation of TROP2 ADC in all subtypes of breast cancer.

NTRK1 Fusions identified by non-invasive plasma next-generation sequencing (NGS) across 9 cancer types.

BACKGROUND: Activating fusions of the NTRK1, NTRK2 and NTRK3 genes are drivers of carcinogenesis and proliferation across a broad range of tumour types in both adult and paediatric patients. Recently, the FDA granted tumour-agnostic approvals of TRK inhibitors, larotrectinib and entrectinib, based on significant and durable responses in multiple primary tumour types. Unfortunately, testing rates in clinical practice remain quite low. Adding plasma next-generation sequencing of circulating tumour DNA (ctDNA) to tissue-based testing increases the detection rate of oncogenic drivers and demonstrates high concordance with tissue genotyping. However, the clinical potential of ctDNA analysis to identify NTRK fusion-positive tumours has been largely unexplored. METHODS: We retrospectively reviewed a ctDNA database in advanced stage solid tumours for NTRK1 fusions. RESULTS: NTRK1 fusion events, with nine unique fusion partners, were identified in 37 patients. Of the cases for which clinical data were available, 44% had tissue testing for NTRK1 fusions; the NTRK1 fusion detected by ctDNA was confirmed in tissue in 88% of cases. Here, we report for the first time that minimally-invasive plasma NGS can detect NTRK fusions with a high positive predictive value. CONCLUSION: Plasma ctDNA represents a rapid, non-invasive screening method for this rare genomic target that may improve identification of patients who can benefit from TRK-targeted therapy and potentially identify subsequent on- and off-target resistance mechanisms.

A First-in-Human Phase 1 Study of a Novel Selective Androgen Receptor Modulator (SARM), RAD140, in ER+/HER2- Metastatic Breast Cancer.

INTRODUCTION/BACKGROUND: This first-in-human, phase 1 study aimed to characterize the safety, tolerability, maximum tolerated dose (MTD), pharmacokinetic (PK) profile, and antitumor activity of RAD140, an oral selective androgen receptor (AR) modulator (SARM). PATIENTS AND METHODS: This dose-escalation study with a 3 + 3 design and PK expansion cohort enrolled postmenopausal women with ER+/HER2- metastatic breast cancer (mBC). Serum sex hormone-binding globulin (SHBG) and prostate-specific antigen (PSA) were used as surrogate markers of AR engagement. RESULTS: Twenty-two (21 AR+) heavily pretreated mBC patients were enrolled. Dose levels included 50 mg (n = 6), 100 mg (n = 13), and 150 mg (n = 3) once daily (QD). Most frequent (> 10%) treatment-emergent adverse events (TEAEs) were elevated AST (59.1%), ALT (45.5%), and total blood bilirubin (27.3%), and vomiting, dehydration, and decreased appetite and weight (27.3% each). Grade 3/4 TEAEs occurred in 16 (72.7%) patients and included elevations in AST/ALT and hypophosphatemia (22.7% each). Treatment-related TEAEs occurred in 17 per 22 patients (77.3%); 7 (31.8%) were Grade 3; none were Grade 4. The half-life (t1/2) of 44.7 hours supported QD dosing. At the MTD of 100 mg/day, 1 patient with an ESR1 mutation at baseline had a partial response. Overall, clinical benefit rate at 24 weeks was 18.2%, and median progression-free survival was 2.3 months. SHBG decreased in 18 per 18 patients, and PSA increased in 16 per 20 patients. Paired baseline and on-treatment tumor biopsies demonstrated AR engagement. CONCLUSION: RAD140 is a novel oral AR-targeted agent for the treatment of AR+/ER+/HER2- mBC with an acceptable safety profile and preliminary evidence of target engagement and antitumor activity.

Evaluation of disseminated tumor cells and circulating tumor cells in patients with breast cancer receiving adjuvant zoledronic acid.

We evaluated disseminated tumor cells (DTCs) and circulating tumor cells (CTCs) in patients with stage I-III breast cancer with >4 MM/mL DTC at baseline who received adjuvant zoledronic acid (ZOL). ZOL was administered every 4 weeks for 24 months, and patients underwent bone marrow aspiration at baseline, and 12 and 24 months of ZOL. Complete DTC response (<4 DTC/mL), serial CTCs, survival, recurrence, and toxicity were determined. Forty-five patients received ZOL. Median baseline DTC was 13.3/mL. Significant reduction in median DTC occurred from baseline to 12 months, and 24 months. Complete DTC response was seen in 32% at 12 months, and 26% at 24 months. Nine patients developed recurrence. Baseline DTC > 30/mL and CTC > 0.8/mL were significantly associated with recurrence and death. Serial reduction in DTCs occurred. Higher baseline DTC > 30/mL and CTC > 0.8/mL correlated with recurrence and death.

Novel Therapies for Metastatic Triple-Negative Breast Cancer: Spotlight on Immunotherapy and Antibody-Drug Conjugates.

Background: Triple-negative breast cancer (TNBC) is a biologically heterogeneous disease that is often associated with worse outcomes compared with other subtypes such as hormone receptor-positive tumors and HER2-positive tumors. While chemotherapy remains the mainstay of standard therapy for metastatic TNBC (mTNBC), several novel treatments have been developed over the past few years. In this review article, we review the major developments in the management of patients with mTNBC. Summary: The combination of chemotherapy and immunotherapy is a potential therapeutic option for PD-L1-positive mTNBC, as the FDA recently approved atezolizumab (Tecentriq) and pembrolizumab (Keytruda) in combination with chemotherapy. Also, 2 targeted therapies-olaparib (Lynparza) and talazoparib (Talzenna)-are FDA approved for the management of mTNBC with germline BRCA mutations, and sacituzumab govitecan, an anti-Trop2 antibody-drug conjugate (ADC), was recently approved for previously treated mTNBC. A number of promising therapies are on the horizon, including AKT inhibitors for PI3K-altered TNBC as well as other ADCs. Key Message: The successful clinical development of immunotherapies, PARP inhibitors, and ADCs for the management of mTNBC has improved the survival outcome of patients. Over the coming years, the therapeutic developments in precision medicine will likely change the mTNBC landscape, and might make the current definition of TNBC as breast cancer that is estrogen receptor negative, progesterone receptor negative, and HER2 negative obsolete.

Programmed cell death 1 (PD-1) receptor and programmed death ligand 1 (PD-L1) gene expression in primary breast cancer.

PURPOSE: The interaction of the programmed cell death 1 (PD-1) receptor on tumor-infiltrating lymphocytes with programmed death ligand 1 (PD-L1) on tumor cells downregulates anti-tumor immunity. This study evaluated associations between PD-1 and PD-L1 expression in primary breast cancer, clinical characteristics, and patient outcomes. METHODS: Microarray data from the Investigation of Serial Studies to predict your therapeutic response with imaging and molecular analysis (I-SPY 1) study (n = 149) was used to evaluate PD-1 and PD-L1 expression. Associations with clinical features and chemotherapy response were determined using Kruskal-Wallis and Wilcoxon rank sum tests, respectively. Recurrence-free survival (RFS) associations were determined with the Cox proportional hazard model. Associations of PD-1 and PD-L1 and selected genes associated with breast cancer, as well as a predictor of olaparib response (PARPi-7), were determined in I-SPY 1 and 2 other datasets: METABRIC (n = 1992) and TCGA (n = 817), using Pearson correlations. RESULTS: In I-SPY 1, PD-1 expression was higher in triple-negative breast cancer (TNBC) and HER2 + breast cancer (p = 0.003), and grade 2/3 tumors (p = 0.043), and was associated with pathologic complete response (p = 0.006). PD-L1 expression in the lowest quintile was associated with worse RFS, even after subtype adjustment (HR 2.33, p = 0.01). PD-1 and PD-L1 gene expression correlated with the expression of immune-related genes and PARPi-7. CONCLUSIONS: PD-1 expression is higher in breast cancers with aggressive features such as TNBC. Low PD-L1 expression may be an adverse prognostic factor. PD-1 and PD-L1 gene expression correlates with the expression of immune-related and DNA damage repair genes.

Clinical Outcomes With Abemaciclib After Prior CDK4/6 Inhibitor Progression in Breast Cancer: A Multicenter Experience.

BACKGROUND: Inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6i) are widely used as first-line therapy for hormone receptor-positive metastatic breast cancer (HR+ MBC). Although abemaciclib monotherapy is also FDA-approved for treatment of disease progression on endocrine therapy, there is limited insight into the clinical activity of abemaciclib after progression on prior CDK4/6i. PATIENTS AND METHODS: We identified patients with HR+ MBC from 6 cancer centers in the United States who received abemaciclib after disease progression on prior CDK4/6i, and abstracted clinical features, outcomes, toxicity, and predictive biomarkers. RESULTS: In the multicenter cohort, abemaciclib was well tolerated after a prior course of CDK4/6i (palbociclib)-based therapy; a minority of patients discontinued abemaciclib because of toxicity without progression (9.2%). After progression on palbociclib, most patients (71.3%) received nonsequential therapy with abemaciclib (with ≥1 intervening non-CDK4/6i regimens), with most receiving abemaciclib with an antiestrogen agent (fulvestrant, 47.1%; aromatase inhibitor, 27.6%), and the remainder receiving abemaciclib monotherapy (19.5%). Median progression-free survival for abemaciclib in this population was 5.3 months and median overall survival was 17.2 months, notably similar to results obtained in the MONARCH-1 study of abemaciclib monotherapy in heavily pretreated HR+/HER2-negative CDK4/6i-naïve patients. A total of 36.8% of patients received abemaciclib for ≥6 months. There was no relationship between the duration of clinical benefit while on palbociclib and the subsequent duration of treatment with abemaciclib. RB1, ERBB2, and CCNE1 alterations were noted among patients with rapid progression on abemaciclib. CONCLUSIONS: A subset of patients with HR+ MBC continue to derive clinical benefit from abemaciclib after progression on prior palbociclib. These results highlight the need for future studies to confirm molecular predictors of cross-resistance to CDK4/6i therapy and to better characterize the utility of abemaciclib after disease progression on prior CDK4/6i.

Clinical application of liquid biopsies to detect somatic BRCA1/2 mutations and guide potential therapeutic intervention for patients with metastatic breast cancer.

Plasma based genotyping via cell-free DNA may identify actionable mutations for potential therapeutic intervention in patients with advanced malignancies including breast cancer. In this article, we discuss recent studies using cell-free DNA testing to identify and classify somatic BRCA1/2 mutations in metastatic breast cancer, and potential future applications for the treatment of metastatic breast cancer.

Tumor Tissue- versus Plasma-based Genotyping for Selection of Matched Therapy and Impact on Clinical Outcomes in Patients with Metastatic Breast Cancer.

PURPOSE: Actionable mutations can guide genotype-directed matched therapy. We evaluated the utility of tissue-based and plasma-based genotyping for the identification of actionable mutations and selection of matched therapy in patients with metastatic breast cancer (MBC). EXPERIMENTAL DESIGN: Patients with MBC who underwent tissue genotyping (institutional platform, 91-gene assay) or plasma-based cell-free DNA (cfDNA, Guardant360, 73-gene assay) between January 2016 and December 2017 were included. A chart review of records to identify subtype, demographics, treatment, outcomes, and tissue genotyping or cfDNA results was performed. The incidence of actionable mutations and the selection of matched therapy in tissue genotyping or cfDNA cohorts was determined. The impact of matched therapy status on overall survival (OS) in tissue genotyping or cfDNA subgroups was determined with Cox regression analysis. RESULTS: Of 252 patients who underwent cfDNA testing, 232 (92%) had detectable mutations, 196 (78%) had actionable mutations, and 86 (34%) received matched therapy. Of 118 patients who underwent tissue genotyping, 90 (76%) had detectable mutations, 59 (50%) had actionable mutations, and 13 (11%) received matched therapy. For cfDNA patients with actionable mutations, matched versus nonmatched therapy was associated with better OS [HR 0.41, 95% confidence interval (CI): 0.23-0.73, P = 0.002], and this remained significant in a multivariable analysis correcting for age, subtype, visceral metastases, and brain metastases (HR = 0.46, 95% CI: 0.26-0.83, P = 0.010). CONCLUSIONS: Plasma-based genotyping identified high rates of actionable mutations, which was associated with significant application of matched therapy and better OS in patients with MBC.See related commentary by Rugo and Huppert, p. 3275.

Novel Agents for Metastatic Triple-Negative Breast Cancer: Finding the Positive in the Negative.

Metastatic triple-negative breast cancer (TNBC) is associated with a poor prognosis, and the development of better therapeutics represents a major unmet clinical need. Although the mainstay of treatment of metastatic TNBC is chemotherapy, advances in genomics and molecular profiling have helped better define subtypes of TNBC with distinct biologic drivers to guide the therapeutic development of targeted therapies, including AKT inhibitors for PI3K/AKT-altered TNBC, checkpoint inhibitors for PD-L1-positive TNBC, and PARP inhibitors for BRCA1/2 mutant TNBC. This progress may ultimately convert TNBC from a disease traditionally defined by the absence of therapeutically actionable receptors to one that is defined by the presence of discrete molecular targets with therapeutic implications. Furthermore, antibody drug conjugates have emerged as an important therapeutic strategy to target genomically complex tumors that lack actionable oncogenes but have overexpressed actionable surface receptors such as trop-2. In this article, we discuss promising novel agents for advanced TNBC, some of which have been incorporated into current clinical practice, and others that will likely change the therapeutic landscape and redefine the TNBC terminology in the near future.

Identification of Somatically Acquired BRCA1/2 Mutations by cfDNA Analysis in Patients with Metastatic Breast Cancer.

PURPOSE: Plasma genotyping may identify mutations in potentially "actionable" cancer genes, such as BRCA1/2, but their clinical significance is not well-defined. We evaluated the characteristics of somatically acquired BRCA1/2 mutations in patients with metastatic breast cancer (MBC). EXPERIMENTAL DESIGN: Patients with MBC undergoing routine cell-free DNA (cfDNA) next-generation sequencing (73-gene panel) before starting a new therapy were included. Somatic BRCA1/2 mutations were classified as known germline pathogenic mutations or novel variants, and linked to clinicopathologic characteristics. The effect of the PARP inhibitor, olaparib, was assessed in vitro, using cultured circulating tumor cells (CTCs) from a patient with a somatically acquired BRCA1 mutation and a second patient with an acquired BRCA2 mutation. RESULTS: Among 215 patients with MBC, 29 (13.5%) had somatic cfDNA BRCA1/2 mutations [nine (4%) known germline pathogenic and rest (9%) novel variants]. Known germline pathogenic BRCA1/2 mutations were common in younger patients (P = 0.008), those with triple-negative disease (P = 0.022), and they were more likely to be protein-truncating alterations and be associated with TP53 mutations. Functional analysis of a CTC culture harboring a somatic BRCA1 mutation demonstrated high sensitivity to PARP inhibition, while another CTC culture harboring a somatic BRCA2 mutation showed no differential sensitivity. Across the entire cohort, APOBEC mutational signatures (COSMIC Signatures 2 and 13) and the "BRCA" mutational signature (COSMIC Signature 3) were present in BRCA1/2-mutant and wild-type cases, demonstrating the high mutational burden associated with advanced MBC. CONCLUSIONS: Somatic BRCA1/2 mutations are readily detectable in MBC by cfDNA analysis, and may be present as both known germline pathogenic and novel variants.