Tumor Fusion Burden as a Hallmark of Immune Infiltration in Prostate Cancer.

Prostate cancer is the second leading cause of cancer-related death in men. Despite having a relatively lower tumor mutational burden than most tumor types, multiple gene fusions such as TMPRSS2:ERG have been characterized and linked to more aggressive disease. Individual tumor samples have been found to contain multiple fusions, and it remains unknown whether these fusions increase tumor immunogenicity. Here, we investigated the role of fusion burden on the prevalence and expression of key molecular and immune effectors in prostate cancer tissue specimens that represented the different stages of disease progression and androgen sensitivity, including hormone-sensitive and castration-resistant prostate cancer. We found that tumor fusion burden was inversely correlated with tumor mutational burden and not associated with disease stage. High fusion burden correlated with high immune infiltration, PD-L1 expression on immune cells, and immune signatures, representing activation of T cells and M1 macrophages. High fusion burden inversely correlated with immune-suppressive signatures. Our findings suggest that high tumor fusion burden may be a more appropriate biomarker than tumor mutational burden in prostate cancer, as it more closely associates with immunogenicity, and suggests that tumors with high fusion burden could be potential candidates for immunotherapeutic agents.

Genomic Analysis of Circulating Tumor Cells at the Single-Cell Level.

Circulating tumor cells (CTCs) have a great potential for noninvasive diagnosis and real-time monitoring of cancer. A comprehensive evaluation of four whole genome amplification (WGA)/next-generation sequencing workflows for genomic analysis of single CTCs, including PCR-based (GenomePlex and Ampli1), multiple displacement amplification (Repli-g), and hybrid PCR- and multiple displacement amplification-based [multiple annealing and loop-based amplification cycling (MALBAC)] is reported herein. To demonstrate clinical utilities, copy number variations (CNVs) in single CTCs isolated from four patients with squamous non-small-cell lung cancer were profiled. Results indicate that MALBAC and Repli-g WGA have significantly broader genomic coverage compared with GenomePlex and Ampli1. Furthermore, MALBAC coupled with low-pass whole genome sequencing has better coverage breadth, uniformity, and reproducibility and is superior to Repli-g for genome-wide CNV profiling and detecting focal oncogenic amplifications. For mutation analysis, none of the WGA methods were found to achieve sufficient sensitivity and specificity by whole exome sequencing. Finally, profiling of single CTCs from patients with non-small-cell lung cancer revealed potentially clinically relevant CNVs. In conclusion, MALBAC WGA coupled with low-pass whole genome sequencing is a robust workflow for genome-wide CNV profiling at single-cell level and has great potential to be applied in clinical investigations. Nevertheless, data suggest that none of the evaluated single-cell sequencing workflows can reach sufficient sensitivity or specificity for mutation detection required for clinical applications.

Predictive and Pharmacodynamic Biomarkers of Response to the Phosphatidylinositol 3-Kinase Inhibitor Taselisib in Breast Cancer Preclinical Models.

The PI3K signaling pathway serves as a central node in regulating cell survival, proliferation, and metabolism. PIK3CA, the gene encoding the PI3K catalytic subunit p110-alpha, is commonly altered in breast cancer resulting in the constitutive activation of the PI3K pathway. Using an unbiased cell line screening approach, we tested the sensitivity of breast cancer cell lines to taselisib, a potent PI3K inhibitor, and correlated sensitivity with key biomarkers (PIK3CA, HER2, PTEN, and ESR1). We further assessed how taselisib modulates downstream signaling in the different genomic backgrounds that occur within breast cancer. We found that sensitivity to taselisib correlated with the presence of PIK3CA mutations, but was independent of HER2 status. We further showed that HER2-amplified/PIK3CA wild-type cell lines are not as sensitive to taselisib when compared with HER2-amplified/PIK3CA-mutant cell lines. In a PIK3CA-mutant/PTEN null background, PI3K downstream signaling rebounded in the presence of taselisib correlating with decreased sensitivity at later time points. Finally, we observed that PIK3CA mutations cooccurred with mutations in the estrogen receptor (ER; ESR1) in metastatic tumors from patients with ER+ breast cancer. However, the cooccurrence of an ESR1 mutation with a PIK3CA mutation did not affect response to taselisib in a single agent setting or in combination with fulvestrant. In summary, these data suggest that development of taselisib in breast cancer should occur in a PIK3CA-mutant setting with cotreatments determined by the specific subtypes under investigation.

CBP/p300 Drives the Differentiation of Regulatory T Cells through Transcriptional and Non-Transcriptional Mechanisms.

Regulatory T cells (Treg) are immunosuppressive and negatively impact response to cancer immunotherapies. CREB-binding protein (CBP) and p300 are closely related acetyltransferases and transcriptional coactivators. Here, we evaluate the mechanisms by which CBP/p300 regulate Treg differentiation and the consequences of CBP/p300 loss-of-function mutations in follicular lymphoma. Transcriptional and epigenetic profiling identified a cascade of transcription factors essential for Treg differentiation. Mass spectrometry analysis showed that CBP/p300 acetylates prostacyclin synthase, which regulates Treg differentiation by altering proinflammatory cytokine secretion by T and B cells. Reduced Treg presence in tissues harboring CBP/p300 loss-of-function mutations was observed in follicular lymphoma. Our findings provide novel insights into the regulation of Treg differentiation by CBP/p300, with potential clinical implications on alteration of the immune landscape. SIGNIFICANCE: This study provides insights into the dynamic role of CBP/p300 in the differentiation of Tregs, with potential clinical implications in the alteration of the immune landscape in follicular lymphoma.

A Clinically Applicable Gene-Expression Classifier Reveals Intrinsic and Extrinsic Contributions to Consensus Molecular Subtypes in Primary and Metastatic Colon Cancer.

PURPOSE: Four consensus molecular subtypes (CMS1-4) of colorectal cancer were identified in primary tumors and found to be associated with distinctive biological features and clinical outcomes. Given that distant metastasis largely accounts for colorectal cancer-related mortality, we examined the molecular and clinical attributes of CMS in metastatic colorectal cancer (mCRC). EXPERIMENTAL DESIGN: We developed a colorectal cancer-focused NanoString-based CMS classifier that is ideally suited to interrogate archival tissues. We successfully used this panel in the CMS classification of formalin-fixed paraffin-embedded (FFPE) tissues from mCRC cohorts, one of which is composed of paired primary tumors and metastases. Finally, we developed novel mouse implantation models to enable modeling of colorectal cancer in vivo at relevant sites. RESULTS: Using our classifier, we find that the biological hallmarks of mCRC, including CMS, are in general highly similar to those observed in nonmetastatic early-stage disease. Importantly, our data demonstrate that CMS1 has the worst outcome in relapsed disease, compared with other CMS. Assigning CMS to primary tumors and their matched metastases reveals mostly concordant subtypes between primary and metastasis. Molecular analysis of matched discordant pairs reveals differences in stromal composition at each site. The development of two novel in vivo orthotopic implantation models further reinforces the notion that extrinsic factors may impact on CMS identification in matched primary and metastatic colorectal cancer. CONCLUSIONS: We describe the utility of a NanoString panel for CMS classification of FFPE clinical samples. Our work reveals the impact of intrinsic and extrinsic factors on colorectal cancer heterogeneity during disease progression.

Low-pass Whole-genome Sequencing of Circulating Cell-free DNA Demonstrates Dynamic Changes in Genomic Copy Number in a Squamous Lung Cancer Clinical Cohort.

PURPOSE: We developed a method to monitor copy number variations (CNV) in plasma cell-free DNA (cfDNA) from patients with metastatic squamous non-small cell lung cancer (NSCLC). We aimed to explore the association between tumor-derived cfDNA and clinical outcomes, and sought CNVs that may suggest potential resistance mechanisms. EXPERIMENTAL DESIGN: Sensitivity and specificity of low-pass whole-genome sequencing (LP-WGS) were first determined using cell line DNA and cfDNA. LP-WGS was performed on baseline and longitudinal cfDNA of 152 patients with squamous NSCLC treated with chemotherapy, or in combination with pictilisib, a pan-PI3K inhibitor. cfDNA tumor fraction and detected CNVs were analyzed in association with clinical outcomes. RESULTS: LP-WGS successfully detected CNVs in cfDNA with tumor fraction ≥10%, which represented approximately 30% of the first-line NSCLC patients in this study. The most frequent CNVs were gains in chromosome 3q, which harbors the PIK3CA and SOX2 oncogenes. The CNV landscape in cfDNA with a high tumor fraction generally matched that of corresponding tumor tissue. Tumor fraction in cfDNA was dynamic during treatment, and increases in tumor fraction and corresponding CNVs could be detected before radiographic progression in 7 of 12 patients. Recurrent CNVs, such as MYC amplification, were enriched in cfDNA from posttreatment samples compared with the baseline, suggesting a potential resistance mechanism to pictilisib. CONCLUSIONS: LP-WGS offers an unbiased and high-throughput way to investigate CNVs and tumor fraction in cfDNA of patients with cancer. It may also be valuable for monitoring treatment response, detecting disease progression early, and identifying emergent clones associated with therapeutic resistance.

Genomic Alterations Associated with Recurrence and TNBC Subtype in High-Risk Early Breast Cancers.

The identification of early breast cancer patients who may benefit from adjuvant chemotherapy has evolved to include assessment of clinicopathologic features such as tumor size and nodal status, as well as several gene-expression profiles for ER-positive, HER2-negative cancers. However, these tools do not reliably identify patients at the greatest risk of recurrence. The mutation and copy-number landscape of triple-negative breast cancer (TNBC) subtypes defined by gene expression is also largely unknown, and elucidation of this landscape may shed light on novel therapeutic opportunities. The USO01062 phase III clinical trial of standard chemotherapy (with or without capecitabine) enrolled a cohort of putatively high-risk patients based on clinical features, yet only observed a 5-year disease-free survival event rate of 11.6%. In order to uncover genomic aberrations associated with recurrence, a targeted next-generation sequencing panel was used to compare tumor specimens from patients who had a recurrence event with a matched set who did not. The somatic mutation and copy-number alteration landscapes of high-risk early breast cancer patients were characterized and alterations associated with relapse were identified. Tumor mutational burden was evaluated but was not prognostic in this study, nor did it correlate with PDL1 or CD8 gene expression. However, TNBC subtypes had substantial genomic heterogeneity with a distinct pattern of genomic alterations and putative underlying driver mutations. IMPLICATIONS: The present study uncovers a compendium of genomic alterations with utility to more precisely identify high-risk patients for adjuvant trials of novel therapeutic agents.

A transcriptional MAPK Pathway Activity Score (MPAS) is a clinically relevant biomarker in multiple cancer types.

KRAS- and BRAF-mutant tumors are often dependent on MAPK signaling for proliferation and survival and thus sensitive to MAPK pathway inhibitors. However, clinical studies have shown that MEK inhibitors are not uniformly effective in these cancers indicating that mutational status of these oncogenes does not accurately capture MAPK pathway activity. A number of transcripts are regulated by this pathway and are recurrently identified in genome-based MAPK transcriptional signatures. To test whether the transcriptional output of only 10 of these targets could quantify MAPK pathway activity with potential predictive or prognostic clinical utility, we created a MAPK Pathway Activity Score (MPAS) derived from aggregated gene expression. In vitro, MPAS predicted sensitivity to MAPK inhibitors in multiple cell lines, comparable to or better than larger genome-based statistical models. Bridging in vitro studies and clinical samples, median MPAS from a given tumor type correlated with cobimetinib (MEK inhibitor) sensitivity of cancer cell lines originating from the same tissue type. Retrospective analyses of clinical datasets showed that MPAS was associated with the sensitivity of melanomas to vemurafenib (HR: 0.596) and negatively prognostic of overall or progression-free survival in both adjuvant and metastatic CRC (HR: 1.5 and 1.4), adrenal cancer (HR: 1.7), and HER2+ breast cancer (HR: 1.6). MPAS thus demonstrates potential clinical utility that warrants further exploration.

High-Throughput and Sensitive Quantification of Circulating Tumor DNA by Microfluidic-Based Multiplex PCR and Next-Generation Sequencing.

Circulating tumor DNA (ctDNA) has potential to serve as a biomarker for noninvasive monitoring of treatment response and disease progression. However, broad clinical applicability of ctDNA has been limited by the low sensitivity, throughput, and patient coverage offered by existing ctDNA detection methods. Herein, we report the adaptation and characterization of the microfluidics multiplex PCR sequencing technology for high-throughput and sensitive quantitation of ctDNA. A multiplex PCR preamplification step was developed and incorporated into the microfluidics multiplex PCR sequencing work flow to enable low-input ctDNA analysis with enhanced sensitivity. An empirical bayesian model was developed to characterize both position and substitution-associated system errors specific to this platform and provided a tailored approach to greatly enhance the confidence and accuracy of variant calling for ctDNA analysis. Clinical validation of this platform for ctDNA mutation detection demonstrated an overall sensitivity of 92% and specificity of 100% when using mutation calls in the matched tumor tissues as a benchmark. Finally, we established an early proof of concept of clinical utility of this ctDNA work flow for monitoring disease progression using clinical trial samples. Our novel ctDNA work flow provides a high-throughput and sensitive platform that can be implemented in clinical trials for mutation detection and disease monitoring from plasma ctDNA.

A Phase I Dose-Escalation Study of the Safety and Pharmacokinetics of Pictilisib in Combination with Erlotinib in Patients with Advanced Solid Tumors.

BACKGROUND: Epidermal growth factor receptor (EGFR) and phosphatidylinositol 3-kinase (PI3K) are involved in the proliferation and survival of many cancer types. Enhanced antitumor activity may be achieved through combined inhibition of these pathways. We report results for pictilisib (GDC-0941, a class I pan-PI3K inhibitor) plus erlotinib (an EGFR tyrosine kinase inhibitor) in patients with advanced solid tumors. MATERIALS AND METHODS: A 3 + 3 dose-escalation study was carried out at a starting daily dose of 60 mg pictilisib on days 1-21 of a 28-day cycle and 150 mg erlotinib from day 2 of cycle 1. The primary objectives of the study were to assess safety and tolerability, identify dose-limiting toxicities (DLTs), estimate the maximum tolerated dose, and identify the recommended phase II dose (RP2D). Evaluation of a dose-expansion cohort at the RP2D was performed. RESULTS: Fifty-seven patients were treated in the study. All patients experienced at least one adverse event (AE). Grade ≥3 AEs, serious AEs, and deaths were reported in 38 (66.7%), 19 (33.3%), and 4 (7.0%) patients, respectively. DLTs occurred in nine patients across eight cohorts and the RP2D was determined to be 340 mg pictilisib on a "5 days on, 2 days off" schedule plus 100 mg erlotinib. Two patients (3.5%) experienced partial response and 19 (33.3%) had stable disease. CONCLUSION: Combining pictilisib with erlotinib in patients with advanced solid tumors is feasible; however, antitumor activity is limited. Additional studies may identify patients likely to benefit from combined inhibition of EGFR and PI3K pathways. IMPLICATIONS FOR PRACTICE: Combining drugs targeting different signaling pathways in cancer growth and survival could overcome drug resistance and improve antitumor activity. In this first-in-human study for the combination, addition of the PI3K inhibitor pictilisib to the EGFR tyrosine kinase inhibitor erlotinib resulted in toxicity that led to dose and schedule modifications to identify a tolerable recommended phase II dose of 340 mg pictilisib on a "5 days on, 2 days off" schedule plus 100 mg erlotinib daily. The limited antitumor activity observed, however, suggests that additional studies are needed to identify patients most likely to benefit from combined EGFR and PI3K inhibition.

Development and Application of a Microfluidics-Based Panel in the Basal/Luminal Transcriptional Characterization of Archival Bladder Cancers.

In the age of personalized medicine stratifying tumors into molecularly defined subtypes associated with distinctive clinical behaviors and predictable responses to therapies holds tremendous value. Towards this end, we developed a custom microfluidics-based bladder cancer gene expression panel for characterization of archival clinical samples. In silico analysis indicated that the content of our panel was capable of accurately segregating bladder cancers from several public datasets into the clinically relevant basal and luminal subtypes. On a technical level, our bladder cancer panel yielded robust and reproducible results when analyzing formalin-fixed, paraffin-embedded (FFPE) tissues. We applied our panel in the analysis of a novel set of 204 FFPE samples that included non-muscle invasive bladder cancers (NMIBCs), muscle invasive disease (MIBCs), and bladder cancer metastases (METs). We found NMIBCs to be mostly luminal-like, MIBCs to include both luminal- and basal-like types, and METs to be predominantly of a basal-like transcriptional profile. Mutational analysis confirmed the expected enrichment of FGFR3 mutations in luminal samples, and, consistently, FGFR3 IHC showed high protein expression levels of the receptor in these tumors. Our bladder cancer panel enables basal/luminal characterization of FFPE tissues and with further development could be used for stratification of bladder cancer samples in the clinic.

A multicenter, single-arm, open-label, phase 2 study of apitolisib (GDC-0980) for the treatment of recurrent or persistent endometrial carcinoma (MAGGIE study).

BACKGROUND: The current single-arm, open-label trial was designed to evaluate the activity of apitolisib (GDC-0980), a dual phosphoinositide 3-kinase/mammalian target of rapamycin (PI3K/mTOR) inhibitor, in patients with advanced endometrial cancer (EC). METHODS: Patients with recurrent or persistent EC who were treated with 1 to 2 prior lines of chemotherapy but no prior PI3K/mTOR inhibitor received oral apitolisib at a dose of 40 mg daily during 28-day cycles until disease progression or intolerable toxicity occurred. Patients with type I/II diabetes who required insulin were excluded. The primary endpoints were progression-free survival (PFS) at 6 months and objective response rate. RESULTS: A total of 56 women were enrolled, including 13 (23%) with well-controlled diabetes. Reasons for discontinuation were disease progression (24 patients; 43%), adverse events (13 patients; 23%), and withdrawal by subject (12 patients; 21%). Grade 3/4 apitolisib-related adverse events were hyperglycemia (46%), rash (30%), colitis (5%), and pneumonitis (4%) (toxicities were graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events [version 4.0]). The PFS rate at 6 months was 20% (Kaplan-Meier estimate; 95% confidence interval [95% CI], 7%-33%). The objective response rate was 6% (confirmed). The median PFS was 3.5 months (95% CI, 2.7-3.7 months) and the median overall survival was 15.7 months (95% CI, 9.2-17.0 months). Nineteen patients discontinued the study before the first tumor assessment. Dose reductions were required for 4 diabetic (31%) and 18 nondiabetic (42%) patients. Comprehensive molecular profiling of 46 evaluable archival tumor samples demonstrated that 57% of patients had at least 1 alteration in phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA), phosphatase and tensin homolog (PTEN), or AKT1. All 3 patients with a confirmed response had at least 1 alteration in a PI3K pathway gene. CONCLUSIONS: The antitumor activity noted with the use of a dose of 40 mg of apitolisib daily was limited by tolerability, especially in diabetic patients. Patients with PI3K pathway mutations may have derived enhanced benefit from apitolisib. Cancer 2016;122:3519-28. © 2016 American Cancer Society.

The selective estrogen receptor downregulator GDC-0810 is efficacious in diverse models of ER+ breast cancer.

ER-targeted therapeutics provide valuable treatment options for patients with ER+ breast cancer, however, current relapse and mortality rates emphasize the need for improved therapeutic strategies. The recent discovery of prevalent ESR1 mutations in relapsed tumors underscores a sustained reliance of advanced tumors on ERα signaling, and provides a strong rationale for continued targeting of ERα. Here we describe GDC-0810, a novel, non-steroidal, orally bioavailable selective ER downregulator (SERD), which was identified by prospectively optimizing ERα degradation, antagonism and pharmacokinetic properties. GDC-0810 induces a distinct ERα conformation, relative to that induced by currently approved therapeutics, suggesting a unique mechanism of action. GDC-0810 has robust in vitro and in vivo activity against a variety of human breast cancer cell lines and patient derived xenografts, including a tamoxifen-resistant model and those that harbor ERα mutations. GDC-0810 is currently being evaluated in Phase II clinical studies in women with ER+ breast cancer.

Heterogeneity and clinical significance of ESR1 mutations in ER-positive metastatic breast cancer patients receiving fulvestrant.

Mutations in ESR1 have been associated with resistance to aromatase inhibitor (AI) therapy in patients with ER+ metastatic breast cancer. Little is known of the impact of these mutations in patients receiving selective oestrogen receptor degrader (SERD) therapy. In this study, hotspot mutations in ESR1 and PIK3CA from ctDNA were assayed in clinical trial samples from ER+ metastatic breast cancer patients randomized either to the SERD fulvestrant or fulvestrant plus a pan-PI3K inhibitor. ESR1 mutations are present in 37% of baseline samples and are enriched in patients with luminal A and PIK3CA-mutated tumours. ESR1 mutations are often polyclonal and longitudinal analysis shows distinct clones exhibiting divergent behaviour over time. ESR1 mutation allele frequency does not show a consistent pattern of increases during fulvestrant treatment, and progression-free survival is not different in patients with ESR1 mutations compared with wild-type patients. ESR1 mutations are not associated with clinical resistance to fulvestrant in this study.

Randomized Open-Label Phase II Trial of Apitolisib (GDC-0980), a Novel Inhibitor of the PI3K/Mammalian Target of Rapamycin Pathway, Versus Everolimus in Patients With Metastatic Renal Cell Carcinoma.

PURPOSE: To the best of our knowledge, this study is the first to compare dual inhibition of PI3K/mammalian target of rapamycin (mTOR) by apitolisib (GDC-0980) against single inhibition of mTORC1 by everolimus in metastatic renal cell carcinoma (mRCC). PATIENTS AND METHODS: Patients with clear-cell mRCC who progressed on or after vascular endothelial growth factor-targeted therapy were randomly assigned to apitolisib 40 mg once per day or to everolimus 10 mg once per day. End points included progression-free survival, safety, overall survival, and objective response rate. Biomarker assessments were conducted. RESULTS: Eighty-five patients were randomly assigned. After 67 events, stratified analysis revealed that median progression-free survival was significantly shorter for apitolisib than for everolimus (3.7 v 6.1 months; hazard ratio, 2.12 [95% CI, 1.23 to 3.63; P < .01]); apitolisib was not favored in any stratification subgroup. Median overall survival was not significantly different but trended in favor of everolimus (16.5 v 22.8 months; hazard ratio, 1.77 [95% CI, 0.97 to 3.24; P = .06]). The objective response rate was 7.1% for apitolisib and 11.6% for everolimus. Patients administered apitolisib with a greater incidence of grade 3 to 4 adverse events were more likely to discontinue treatment (31% v 12% for everolimus). No drug-related deaths were observed. Apitolisib in comparison with everolimus was associated with substantially more high-grade hyperglycemia (40% v 9%) and rash (24% v 2%). Apitolisib pharmacokinetics suggested a relationship between exposure, and rash and hyperglycemia. Retrospective biomarker analyses revealed a relationship between VHL mutation status and outcome with everolimus but not with apitolisib. High hypoxia-inducible factor 1α protein expression was associated with better outcome in both arms. CONCLUSION: This study demonstrated that dual PI3K/mTOR inhibition by apitolisib was less effective than was everolimus in mRCC, likely because full blockade of PI3K/mTOR signaling resulted in multiple on-target adverse events. VHL mutation and hypoxia-inducible factor 1α expression may be predictive of an mTOR inhibitor benefit, although prospective validation is required.

Phase II Randomized Preoperative Window-of-Opportunity Study of the PI3K Inhibitor Pictilisib Plus Anastrozole Compared With Anastrozole Alone in Patients With Estrogen Receptor-Positive Breast Cancer.

PURPOSE: Preclinical data support a key role for the PI3K pathway in estrogen receptor-positive breast cancer and suggest that combining PI3K inhibitors with endocrine therapy may overcome resistance. This preoperative window study assessed whether adding the PI3K inhibitor pictilisib (GDC-0941) can increase the antitumor effects of anastrozole in primary breast cancer and aimed to identify the most appropriate patient population for combination therapy. PATIENTS AND METHODS: In this randomized, open-label phase II trial, postmenopausal women with newly diagnosed operable estrogen receptor-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancers were recruited. Participants were randomly allocated (2:1, favoring the combination) to 2 weeks of preoperative treatment with anastrozole 1 mg once per day (n = 26) or the combination of anastrozole 1 mg with pictilisib 260 mg once per day (n = 49). The primary end point was inhibition of tumor cell proliferation as measured by change in Ki-67 protein expression between tumor samples taken before and at the end of treatment. RESULTS: There was significantly greater geometric mean Ki-67 suppression of 83.8% (one-sided 95% CI, ≥ 79.0%) for the combination and 66.0% (95% CI, ≤ 75.4%) for anastrozole (geometric mean ratio [combination:anastrozole], 0.48; 95% CI, ≤ 0.72; P = .004). PIK3CA mutations were not predictive of response to pictilisib, but there was significant interaction between response to treatment and molecular subtype (P = .03); for patients with luminal B tumors, the combination:anastrozole geometric mean ratio of Ki-67 suppression was 0.37 (95% CI, ≤ 0.67; P = .008), whereas no significant Ki-67 response was observed for pictilisib in luminal A tumors (1.01; P = .98). Multivariable analysis confirmed Ki-67 response to the combination treatment of patients with luminal B tumors irrespective of progesterone receptor status or baseline Ki-67 expression. CONCLUSION: Adding pictilisib to anastrozole significantly increases suppression of tumor cell proliferation in luminal B primary breast cancer.

Activating Mutations in PIK3CB Confer Resistance to PI3K Inhibition and Define a Novel Oncogenic Role for p110ß.

Activation of the PI3K pathway occurs commonly in a wide variety of cancers. Experience with other successful targeted agents suggests that clinical resistance is likely to arise and may reduce the durability of clinical benefit. Here, we sought to understand mechanisms underlying resistance to PI3K inhibition in PTEN-deficient cancers. We generated cell lines resistant to the pan-PI3K inhibitor GDC-0941 from parental PTEN-null breast cancer cell lines and identified a novel PIK3CB D1067Y mutation in both cell lines that was recurrent in cancer patients. Stable expression of mutant PIK3CB variants conferred resistance to PI3K inhibition that could be overcome by downstream AKT or mTORC1/2 inhibitors. Furthermore, we show that the p110ß D1067Y mutant was highly activated and induced PIP3 levels at the cell membrane, subsequently promoting the localization and activation of AKT and PDK1 at the membrane and driving PI3K signaling to a level that could withstand treatment with proximal inhibitors. Finally, we demonstrate that the PIK3CB D1067Y mutant behaved as an oncogene and transformed normal cells, an activity that was enhanced by PTEN depletion. Collectively, these novel preclinical and clinical findings implicate the acquisition of activating PIK3CB D1067 mutations as an important event underlying the resistance of cancer cells to selective PI3K inhibitors.

The molecular landscape of high-risk early breast cancer: comprehensive biomarker analysis of a phase III adjuvant population.

Breast cancer is a heterogeneous disease and patients are managed clinically based on ER, PR, HER2 expression, and key risk factors. We sought to characterize the molecular landscape of high-risk breast cancer patients enrolled onto an adjuvant chemotherapy study to understand how disease subsets and tumor immune status impact survival. DNA and RNA were extracted from 861 breast cancer samples from patients enrolled onto the United States Oncology trial 01062. Samples were characterized using multiplex gene expression, copy number, and qPCR mutation assays. HR+ patients with a PIK3CA mutant tumor had a favorable disease-free survival (DFS; HR 0.66, P=0.05), however, the prognostic effect was specific to luminal A patients (Luminal A: HR 0.67, P=0.1; Luminal B: HR 1.01, P=0.98). Molecular subtyping of triple-negative breast cancers (TNBCs) suggested that the mesenchymal subtype had the worst DFS, whereas the immunomodulatory subtype had the best DFS. Profiling of immunologic genes revealed that TNBC tumors (n=280) displaying an activated T-cell signature had a longer DFS following adjuvant chemotherapy (HR 0.59, P=0.04), while a distinct set of immune genes was associated with DFS in HR+ cancers. Utilizing a discovery approach, we identified genes associated with a high risk of recurrence in HR+ patients, which were validated in an independent data set. Molecular classification based on PAM50 and TNBC subtyping stratified clinical high-risk patients into distinct prognostic subsets. Patients with high expression of immune-related genes showed superior DFS in both HR+ and TNBC. These results may inform patient management and drug development in early breast cancer.

Patients with Slowly Proliferative Early Breast Cancer Have Low Five-Year Recurrence Rates in a Phase III Adjuvant Trial of Capecitabine.

PURPOSE: We conducted a randomized phase III study to determine whether patients with early breast cancer would benefit from the addition of capecitabine (X) to a standard regimen of doxorubicin (A) plus cyclophosphamide (C) followed by docetaxel (T). EXPERIMENTAL DESIGN: Treatment comprised eight cycles of AC→T (T dose: 100 mg/m(2) on day 1) or AC→XT (X dose: 825 mg/m(2) twice daily, days 1-14; T dose: 75 mg/m(2) on day 1). The primary endpoint was 5-year disease-free survival (DFS). RESULTS: Of 2,611 women, 1,304 were randomly assigned to receive AC→T and 1,307 to receive AC→XT. After a median follow-up of 5 years, the study failed to meet its primary endpoint [HR, 0.84; 95% confidence interval (CI), 0.67-1.05; P = 0.125]. A significant improvement in overall survival, a secondary endpoint, was seen with AC→XT versus AC→T (HR, 0.68; 95% CI, 0.51-0.92; P = 0.011). There were no unexpected adverse events. Of patients with estrogen receptor (ER)-positive/HER2-negative disease, 70% of whom were node-positive, 26% and 59% had tumors with a centrally assessed Ki-67 score of <10% or <20%, respectively, and only 17 (2%) and 53 (6%) DFS events, respectively, occurred in these groups at 7 years. CONCLUSIONS: The very low event rate in patients with ER-positive, low Ki-67 cancers, regardless of nodal status, strongly suggests that these patients should not be enrolled in adjuvant trials that assess 5-year DFS rates and that central Ki-67 analyses can identify these patients.