J. Baselga

PI3K inhibition results in enhanced HER signaling and acquired ERK dependency in HER2-overexpressing breast cancer.

There is a strong rationale to therapeutically target the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway in breast cancer since it is highly deregulated in this disease and it also mediates resistance to anti-HER2 therapies. However, initial studies with rapalogs, allosteric inhibitors of mTORC1, have resulted in limited clinical efficacy probably due to the release of a negative regulatory feedback loop that triggers AKT and ERK signaling. Since activation of AKT occurs via PI3K, we decided to explore whether PI3K inhibitors prevent the activation of these compensatory pathways. Using HER2-overexpressing breast cancer cells as a model, we observed that PI3K inhibitors abolished AKT activation. However, PI3K inhibition resulted in a compensatory activation of the ERK signaling pathway. This enhanced ERK signaling occurred as a result of activation of HER family receptors as evidenced by induction of HER receptors dimerization and phosphorylation, increased expression of HER3 and binding of adaptor molecules to HER2 and HER3. The activation of ERK was prevented with either MEK inhibitors or anti-HER2 monoclonal antibodies and tyrosine kinase inhibitors. Combined administration of PI3K inhibitors with either HER2 or MEK inhibitors resulted in decreased proliferation, enhanced cell death and superior anti-tumor activity compared with single agent PI3K inhibitors. Our findings indicate that PI3K inhibition in HER2-overexpressing breast cancer activates a new compensatory pathway that results in ERK dependency. Combined anti-MEK or anti-HER2 therapy with PI3K inhibitors may be required in order to achieve optimal efficacy in HER2-overexpressing breast cancer. This approach warrants clinical evaluation.

PI3K inhibition results in enhanced estrogen receptor function and dependence in hormone receptor–positive breast cancer

Inhibition of the PI3K/AKT pathway results in induction of ER-dependent transcriptional activity and susceptibility to anti-estrogen therapy in ER-positive breast cancer. PIKing the correct therapeutic combination Mutations in a gene called PIK3CA are very common in estrogen receptor–positive breast cancers, and drugs that inhibit PI3K, the protein product of this gene, are already in clinical development. Unfortunately, these drugs are not always effective, and this study by Bosch et al. demonstrates a reason for this problem and a practical way to overcome it. By studying both mouse models and human patients’ tumors, the authors discovered that inhibition of PI3K often stimulates the activity of the estrogen receptor, which then drives tumor growth. By combining PI3K inhibitors with clinically available drugs that inhibit the estrogen receptor, the authors were able to overcome treatment resistance and effectively induce tumor regression in mouse models. Activating mutations of PIK3CA are the most frequent genomic alterations in estrogen receptor (ER)–positive breast tumors, and selective phosphatidylinositol 3-kinase α (PI3Kα) inhibitors are in clinical development. The activity of these agents, however, is not homogeneous, and only a fraction of patients bearing PIK3CA-mutant ER-positive tumors benefit from single-agent administration. Searching for mechanisms of resistance, we observed that suppression of PI3K signaling results in induction of ER-dependent transcriptional activity, as demonstrated by changes in expression of genes containing ER-binding sites and increased occupancy by the ER of promoter regions of up-regulated genes. Furthermore, expression of ESR1 mRNA and ER protein were also increased upon PI3K inhibition. These changes in gene expression were confirmed in vivo in xenografts and patient-derived models and in tumors from patients undergoing treatment with the PI3Kα inhibitor BYL719. The observed effects on transcription were enhanced by the addition of estradiol and suppressed by the anti-ER therapies fulvestrant and tamoxifen. Fulvestrant markedly sensitized ER-positive tumors to PI3Kα inhibition, resulting in major tumor regressions in vivo. We propose that increased ER transcriptional activity may be a reactive mechanism that limits the activity of PI3K inhibitors and that combined PI3K and ER inhibition is a rational approach to target these tumors.

Implementing genome-driven oncology

Early successes in identifying and targeting individual oncogenic drivers, together with the increasing feasibility of sequencing tumor genomes, have brought forth the promise of genome-driven oncology care. As we expand the breadth and depth of genomic analyses, the biological and clinical complexity of its implementation will be unparalleled. Challenges include target credentialing and validation, implementing drug combinations, clinical trial designs, targeting tumor heterogeneity, and deploying technologies beyond DNA sequencing, among others. We review how contemporary approaches are tackling these challenges and will ultimately serve as an engine for biological discovery and increase our insight into cancer and its treatment.

Abstract S6-01: PIK3CA status in circulating tumor DNA (ctDNA) predicts efficacy of buparlisib (BUP) plus fulvestrant (FULV) in postmenopausal women with endocrine-resistant HR+/HER2– advanced breast cancer (BC): First results from the randomized, phase III BELLE-2 trial

Background: PI3K pathway activation is a hallmark of hormone receptor-positive (HR+) BC cells resistant to endocrine therapy (ET). Preclinical and early clinical data suggest that combining the pan-PI3K inhibitor BUP (BKM120) with ET may provide clinical benefits in this setting. BELLE-2 (NCT01610284) is the first randomized Phase III trial to assess the efficacy and safety of a PI3K inhibitor combined with FULV in HR+ advanced BC, including a prospective analysis of whether PI3K pathway activation status measured in archival tumor tissue and ctDNA is predictive of clinical benefit. Methods: Postmenopausal women with HR+/HER2– locally advanced or metastatic BC refractory to aromatase inhibitor therapy were enrolled. After a 14-day run-in with FULV (500 mg), patients (pts) were randomized (1:1) to receive oral BUP (100 mg/day) or placebo (PBO) with FULV (500 mg per standard of care). Randomization of all pts was stratified by PI3K pathway status measured in archival tumor tissue (PIK3CA mutation or PTEN loss; activated, non-activated, unknown) and visceral disease status (present, absent). Baseline PIK3CA mutation status in ctDNA was assessed in a subset of 587 pts at trial entry. The primary endpoint was locally-assessed progression-free survival (PFS; RECIST v1.1) in the full population and PI3K pathway-activated group. Secondary endpoints included overall survival, safety, overall response rate (ORR), and clinical benefit rate (CBR). Results: 1147 pts received FULV with BUP or PBO, with 187 (16%) ongoing at data cut-off. Baseline characteristics were well balanced between the two arms: median age was 62 years, 98% had ECOG performance status of 0/1, 61% had visceral disease, 69% were sensitive to prior ET, 28% had received prior chemotherapy for metastatic BC. BELLE-2 met its primary endpoint in the full population (Table). In pts with PI3K pathway-activated tumor tissue, PFS increase for BUP+FULV vs PBO+FULV did not meet the planned endpoint. Among pts with PIK3CA status measured in ctDNA, median PFS, ORR, and CBR were significantly improved for BUP+FULV vs PBO+FULV in pts with PIK3CA-mutant tumors but not pts without. The most common Grade 3/4 adverse events (AEs; ≥5% of pts; BUP+FULV vs PBO+FULV) in all pts were increased alanine aminotransferase (26 vs 1%), increased aspartate aminotransferase (18 vs 3%), hyperglycemia (15 vs 0.2%), and rash (8 vs 0%). The most common reasons for treatment discontinuation were disease progression (54 vs 73%) and AEs (13 vs 2%). Conclusions: BELLE-2 met its primary endpoint in the full population. Prespecified analyses showed that characterizing PIK3CA mutation in ctDNA at trial entry identifies pts with endocrine- resistant HR+/HER2–advanced BC, for whom BUP+FULV results in meaningful clinical benefits. Citation Format: Baselga J, Im S-A, Iwata H, Clemons M, Ito Y, Awada A, Chia S, Jagiello-Gruszfeld A, Pistilli B, Tseng L-M, Hurvitz S, Masuda N, Cortes J, De Laurentiis M, Arteaga CL, Jiang Z, Jonat W, Hachemi S, Le Mouhaer S, Di Tomaso E, Urban P, Massacesi C, Campone M. PIK3CA status in circulating tumor DNA (ctDNA) predicts efficacy of buparlisib (BUP) plus fulvestrant (FULV) in postmenopausal women with endocrine-resistant HR+/HER2– advanced breast cancer (BC): First results from the randomized, phase III BELLE-2 trial. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr S6-01.

Therapy-Related Clonal Hematopoiesis in Patients with Non-hematologic Cancers Is Common and Associated with Adverse Clinical Outcomes

Clonal hematopoiesis (CH), as evidenced by recurrent somatic mutations in leukemia-associated genes, commonly occurs among aging human hematopoietic stem cells. We analyzed deep-coverage, targeted, next-generation sequencing (NGS) data of paired tumor and blood samples from 8,810 individuals to assess the frequency and clinical relevance of CH in patients with non-hematologic malignancies. We identified CH in 25% of cancer patients, with 4.5% harboring presumptive leukemia driver mutations (CH-PD). CH was associated with increased age, prior radiation therapy, and tobacco use. PPM1D and TP53 mutations were associated with prior exposure to chemotherapy. CH and CH-PD led to an increased incidence of subsequent hematologic cancers, and CH-PD was associated with shorter patient survival. These data suggest that CH occurs in an age-dependent manner and that specific perturbations can enhance fitness of clonal hematopoietic stem cells, which can impact outcome through progression to hematologic malignancies and through cell-non-autonomous effects on solid tumor biology.

Mutation Detection in Patients With Advanced Cancer by Universal Sequencing of Cancer-Related Genes in Tumor and Normal DNA vs Guideline-Based Germline Testing

Importance Guidelines for cancer genetic testing based on family history may miss clinically actionable genetic changes with established implications for cancer screening or prevention. Objective To determine the proportion and potential clinical implications of inherited variants detected using simultaneous sequencing of the tumor and normal tissue (“tumor-normal sequencing”) compared with genetic test results based on current guidelines. Design, Setting, and Participants From January 2014 until May 2016 at Memorial Sloan Kettering Cancer Center, 10 336 patients consented to tumor DNA sequencing. Since May 2015, 1040 of these patients with advanced cancer were referred by their oncologists for germline analysis of 76 cancer predisposition genes. Patients with clinically actionable inherited mutations whose genetic test results would not have been predicted by published decision rules were identified. Follow-up for potential clinical implications of mutation detection was through May 2017. Exposure Tumor and germline sequencing compared with the predicted yield of targeted germline sequencing based on clinical guidelines. Main Outcomes and Measures Proportion of clinically actionable germline mutations detected by universal tumor-normal sequencing that would not have been detected by guideline-directed testing. Results Of 1040 patients, the median age was 58 years (interquartile range, 50.5-66 years), 65.3% were male, and 81.3% had stage IV disease at the time of genomic analysis, with prostate, renal, pancreatic, breast, and colon cancer as the most common diagnoses. Of the 1040 patients, 182 (17.5%; 95% CI, 15.3%-19.9%) had clinically actionable mutations conferring cancer susceptibility, including 149 with moderate- to high-penetrance mutations; 101 patients tested (9.7%; 95% CI, 8.1%-11.7%) would not have had these mutations detected using clinical guidelines, including 65 with moderate- to high-penetrance mutations. Frequency of inherited mutations was related to case mix, stage, and founder mutations. Germline findings led to discussion or initiation of change to targeted therapy in 38 patients tested (3.7%) and predictive testing in the families of 13 individuals (1.3%), including 6 for whom genetic evaluation would not have been initiated by guideline-based testing. Conclusions and Relevance In this referral population with selected advanced cancers, universal sequencing of a broad panel of cancer-related genes in paired germline and tumor DNA samples was associated with increased detection of individuals with potentially clinically significant heritable mutations over the predicted yield of targeted germline testing based on current clinical guidelines. Knowledge of these additional mutations can help guide therapeutic and preventive interventions, but whether all of these interventions would improve outcomes for patients with cancer or their family members requires further study. Trial Registration clinicaltrials.gov Identifier: NCT01775072

AKT Inhibition in Solid Tumors With AKT1 Mutations

Purpose AKT1 E17K mutations are oncogenic and occur in many cancers at a low prevalence. We performed a multihistology basket study of AZD5363, an ATP-competitive pan-AKT kinase inhibitor, to determine the preliminary activity of AKT inhibition in AKT-mutant cancers. Patients and Methods Fifty-eight patients with advanced solid tumors were treated. The primary end point was safety; secondary end points were progression-free survival (PFS) and response according to Response Evaluation Criteria in Solid Tumors (RECIST). Tumor biopsies and plasma cell-free DNA (cfDNA) were collected in the majority of patients to identify predictive biomarkers of response. Results In patients with AKT1 E17K-mutant tumors (n = 52) and a median of five lines of prior therapy, the median PFS was 5.5 months (95% CI, 2.9 to 6.9 months), 6.6 months (95% CI, 1.5 to 8.3 months), and 4.2 months (95% CI, 2.1 to 12.8 months) in patients with estrogen receptor-positive breast, gynecologic, and other solid tumors, respectively. In an exploratory biomarker analysis, imbalance of the AKT1 E17K-mutant allele, most frequently caused by copy-neutral loss-of-heterozygosity targeting the wild-type allele, was associated with longer PFS (hazard ratio [HR], 0.41; P = .04), as was the presence of coincident PI3K pathway hotspot mutations (HR, 0.21; P = .045). Persistent declines in AKT1 E17K in cfDNA were associated with improved PFS (HR, 0.18; P = .004) and response ( P = .025). Responses were not restricted to patients with detectable AKT1 E17K in pretreatment cfDNA. The most common grade ≥ 3 adverse events were hyperglycemia (24%), diarrhea (17%), and rash (15.5%). Conclusion This study provides the first clinical data that AKT1 E17K is a therapeutic target in human cancer. The genomic context of the AKT1 E17K mutation further conditioned response to AZD5363.

Abstract S1-01: The association between event-free survival and pathological complete response to neoadjuvant lapatinib, trastuzumab or their combination in HER2-positive breast cancer. Survival follow-up analysis of the NeoALTTO study (BIG 1-06)

Background: The NeoALTTO study demonstrated a significantly higher breast pathological complete response (pCR) rate (NSABP definition – ypT0/is) with dual HER2 blockade using lapatinib and trastuzumab compared with single HER2 blockade using either lapatinib or trastuzumab (51.3% vs. 24.7% vs. 29.5%, respectively; p Material and Methods: From January, 2008, to December, 2009, 455 patients were randomized from 99 participating sites in 23 countries. Patients were randomized to receive either lapatinib 1500 mg/d (154 pts), or trastuzumab 4 mg/kg IV loading dose followed by 2 mg/kg IV weekly (149 pts), or lapatinib 1000 mg/d with trastuzumab for a total of 6 weeks (152 pts). After this biological window, patients continued on the same targeted therapy plus weekly paclitaxel 80 mg/m2 for a further 12 weeks, until definitive surgery (total neoadjuvant therapy duration of 18 weeks). After surgery, patients received 3 cycles of adjuvant FEC followed by the same targeted therapy as in the biological window of the neoadjuvant phase for a further 34 weeks (to complete 52 weeks of anti-HER2 therapy), with on-going follow-up planned until 10 years after last randomised patient. Secondary objectives included disease-free survival and overall survival (OS). Following current practice and draft FDA recommendations for neoadjuvant trial endpoints, an amendment was made to the protocol secondary objectives (released in May 2013). DFS (from surgery) was replaced by event-free survival (EFS) from randomisation; OS from surgery was correspondingly replaced with OS from randomisation, and examination of the association between these survival endpoints and locoregional pCR (ypT0/is ypN0) was added as a secondary objective. EFS was defined as the time from randomization to first EFS event (breast cancer relapse, second primary malignancy or death without recurrence). OS was defined as the time from randomization to death from any cause. Results: The clinical cut-off date for the first planned analysis of these secondary objectives was on 26 May 2013, three years after the date of last surgery. Data cleaning is ongoing and analysis will be completed by November 2013. Results for EFS, OS and their association with pCR will be presented at the meeting. Funding: GlaxoSmithKline is the sponsor of this trial. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr S1-01.

Pten loss promotes MAPK pathway dependency in HER2/neu breast carcinomas

Significance PTEN mutations are associated with disease progression and therapy resistance in human epidermal growth factor receptor 2 (HER2/neu)-amplified breast cancer patients but the role of PTEN loss in breast cancer maintenance is unknown. Here, using a regulatable RNAi mouse model of HER2/neu-driven metastatic breast cancer, we show that Pten silencing accelerates disease progression and that restoration of endogenous Pten expression triggers marked disease regression. By comparing and contrasting how pharmacologic perturbations of various signaling pathways compare to genetic reactivation of Pten, we identify a requirement for Mek signaling in Pten-suppressed tumors. Our findings imply that even advanced tumors can remain dependent on Pten loss and provide a rationale for exploring the utility of MEK inhibitors in therapy-resistant breast cancer patients acquiring PTEN mutations. Loss of the tumor suppressor gene PTEN is implicated in breast cancer progression and resistance to targeted therapies, and is thought to promote tumorigenesis by activating PI3K signaling. In a transgenic model of breast cancer, Pten suppression using a tetracycline-regulatable short hairpin (sh)RNA cooperates with human epidermal growth factor receptor 2 (HER2/neu), leading to aggressive and metastatic disease with elevated signaling through PI3K and, surprisingly, the mitogen-activated protein kinase (MAPK) pathway. Restoring Pten function is sufficient to down-regulate both PI3K and MAPK signaling and triggers dramatic tumor regression. Pharmacologic inhibition of MAPK signaling produces similar effects to Pten restoration, suggesting that the MAPK pathway contributes to the maintenance of advanced breast cancers harboring Pten loss.

Vemurafenib for BRAF V600-mutant erdheim-chester disease and langerhans cell histiocytosis analysis of data from the histology-independent, phase 2, open-label VE-BASKET study

Importance The histiocytic neoplasms Erdheim-Chester disease (ECD) and Langerhans cell histiocytosis (LCH) are highly enriched for BRAF V600 mutations and have been previously shown to be responsive to treatment with vemurafenib, an inhibitor of the BRAF V600 kinase. However, the long-term efficacy and safety of prolonged vemurafenib use in these patients are not defined. Here we analyze the final efficacy and safety data for vemurafenib in patients with ECD and LCH enrolled in the VE-BASKET study. Objective To determine the efficacy and safety of vemurafenib in adults with ECD or LCH enrolled in the VE-BASKET study. Design, Setting, and Participants The VE-BASKET study was an open-label, nonrandomized, multicohort study for patients with nonmelanoma cancers harboring the BRAF V600 mutation. Patients with BRAF V600–mutant ECD or LCH were enrolled in an “other solid tumor” cohort of the VE-BASKET study, and they were enrolled in the present study. Interventions Patients received vemurafenib, 960 mg, twice daily continuously until disease progression, study withdrawal, or occurrence of intolerable adverse effects. Main Outcomes and Measures The primary end point was confirmed objective response rate (ORR) by Response Evaluation Criteria in Solid Tumors (RECIST, version 1.1). Secondary end points included progression-free survival (PFS), overall survival (OS), metabolic response by modified positron-emission tomography (PET) Response Criteria in Solid Tumors (PERCIST) using 18F-fluorodeoxyglucose (FDG)-PET/computed tomography (CT), and safety. Results A total of 26 patients from the VE-BASKET trial (22 with ECD, 4 with LCH) were included in the present study (14 women and 12 men; median age, 61 years; age range, 51-74 years). The confirmed ORR was 61.5% (95% CI, 40.6%-79.8%) in the overall cohort and 54.5% (95% CI, 32.2%-75.6%) in patients with ECD. All evaluable patients achieved stable disease or better. The median PFS and OS had not been reached in the overall cohort at study closure despite a median follow-up of 28.8 months; 2-year PFS was 86% (95% CI, 72%-100%), and 2-year OS was 96% (95% CI, 87%-100%). All 15 patients evaluated by FDG-PET/CT achieved a metabolic response, including 12 patients (80%) with a complete metabolic response. The most common adverse events (AEs) in the overall cohort included arthralgia, maculopapular rash, fatigue, alopecia, prolonged QT interval, skin papilloma, and hyperkeratosis. Hypertension and dermatologic AEs occurred at higher rates than those reported in metastatic melanoma. Conclusions and Relevance In this study, vemurafenib had prolonged efficacy in patients with BRAF V600–mutant ECD and LCH and warrants consideration as a new standard of care for these patients.