PIK3CA Mutation Test Research Articles

A Phase I Trial of Alpelisib Combined With Capecitabine in Patients With HER2-Negative Metastatic Breast Cancer

BackgroundAlpelisib is an oral α-specific class I PI3K inhibitor approved in combination with fulvestrant for the treatment of PIK3CA-mutated hormone receptor-positive (HR+), human epidermal growth factor receptor 2 negative (HER2-) metastatic breast cancer. The tolerability of this drug with the oral chemotherapy capecitabine is unknown. Patients and MethodsThis phase I trial evaluated the dose-limiting toxicities (DLTs) and maximum tolerated dose (MTD) of alpelisib (250 mg or 300 mg daily for 3-weeks) with capecitabine (1000 mg/m2 twice daily for 2-weeks followed by a 1-week rest period) in patients with metastatic HER2-negative breast cancer, regardless of PIK3CA mutation status. ResultsEighteen patients were treated with alpelisib-capecitabine. Half of the patients had HR+ breast cancer, and 16 had prior systemic therapy for metastatic disease. The MTD of alpelisib was 250 mg daily in combination with capecitabine 1000 mg/m2 twice daily. DLTs included hyperglycemia, QTc prolongation, fatigue, and chest pain. The most common grade 3 adverse event (AE) was hyperglycemia (28%). No grade 4 AEs were observed. Three patients discontinued therapy due to an AE. One-third of patients required dose reduction of both alpelisib and capecitabine. Four patients experienced a partial response and 8 patients experienced stable disease. The median progression-free survival was 9.7 months (95% CI 2.8-13.5 months) and median overall survival was 18.2 months (95% CI 7.2-35.2 months). Twelve patients had PIK3CA mutation testing completed, of these 2 had known or likely deleterious PIK3CA mutation. ConclusionThis study provides safety data for an oral combination therapy of alpelisib-capecitabine and defines tolerable doses for further study.

PIK3CA testing and treatment patterns among patients with metastatic breast cancer in US community clinical practice.

e13059 Background: PIK3CA mutations are present in ~35-40% of HR+/HER2- breast cancer patients. Targeted treatments are approved and in development for patients with advanced disease, and clinical guidelines recommend biomarker testing. This retrospective cohort study characterized PIK3CA mutation testing and treatment patterns among HR+/HER2- metastatic breast cancer (mBC) patients in United States (US) community clinical practices. Methods: We used the nationwide Flatiron Health electronic health record-derived de-identified database to select patients diagnosed with HR+/HER2- mBC from January 2011 to May 2023. We described baseline characteristics of patients tested and not tested for PIK3CA mutation. We captured rates of PIK3CA mutation testing (anytime and ≤1 year) prior to starting first-line (1L), second-line (2L), and third-line (3L) treatment; test and sample types; secular trends over time; and test turnaround time (TAT). Treatment patterns for patients with a PIK3CA-mutated tumor were also described from 2019 onwards. Results: Among 14,246 HR+/HER2- mBC patients treated at community sites, 4,537 had a PIK3CA mutation test result during the study period. 25% of patients had more than one PIK3CA mutation test. Test rates increased from 2011 to 2023 for all patients starting 1L, 2L, or 3L during the study period (Table). In 2023, the percentage of patients tested anytime prior to 1L, 2L, and 3L start dates were 11% (37 of 324 patients), 52% (140 of 271 patients), and 65% (133 of 204 patients), respectively. Among tested patients, those who were tested between 1L and 2L increased from 32% in 2018 to 45% in 2023. Median time from mBC diagnosis date to first test was variable across years: 8, 10, and 3 months in 2018, 2020, and 2022, respectively. During the study period, most PIK3CA mutation tests were next-generation sequencing (NGS) (88%) and used tumor tissue (72%). Median TAT decreased from 12 days in 2018 to 7 days in 2023. Among patients with a PIK3CA-mutated tumor in 2019 and onwards who received treatment, 36% of patients received alpelisib-containing regimens. Conclusions: PIK3CA mutation testing in HR+/HER2- mBC patients has increased over time in community clinical practice, and timing has shifted to earlier lines of therapy among tested patients. However, overall testing and subsequent treatment with pathway-directed therapy are still low despite clinical guidelines, which may reflect potential gaps in access to PIK3CA mutation testing and the continued unmet need regarding available targeted agents within the current treatment landscape. [Table: see text]

Prevalence of somatic PIK3CA mutations in hormone receptor-positive metastatic breast cancer: The Indian experience.

e13047 Background: The phosphatidylinositol 3-kinase (PI3K) inhibitors have been found to improve survival outcomes in hormone receptor-positive metastatic breast cancer (MBC) and are FDA-approved in this setting after progression on hormonal therapy. However, real-world data from India on the prevalence of PIK3CA mutations is scarce. Methods: This is a retrospective study including patients with hormone receptor-positive breast cancer registered at our center between January 2017- and December 2023 who developed metastatic disease on follow-up after getting appropriate treatment (adjuvant /neoadjuvant) as per institutional protocol. The PIK3CA mutation testing was done on the biopsy specimen. FDA-approved therascreen PIL3CA RGQ PCR kit from Qiagen was used and the assay is a real-time qualitative PCR test for the detection of 11 mutations phosphatidylinositol 3-kinase catalytic subunit alpha (PIK3CA) gene (Exon 7: C420R; Exon 9: E542K, E545A, E545D [1635G>T only], E545G, E545K, Q546E, Q546R; and Exon 20: H1047L, H1047R, H1047Y) using genomic DNA (gDNA) extracted from formalin-fixed, paraffin-embedded (FFPE) breast tumor tissue. The clinical demographics of patients with PIK3CA mutations were extracted from the hospital database and represented descriptively. Results: A total of 80 consecutive patients with hormone-positive breast cancer at relapse were screened and 26 were found to have PIK3CA mutations (32.5%) of which 24 were female (92.3%). The median age of patients with mutated PIK3CA cases was 50 years (range: 31 to 72 years). The clinical stage of disease at presentation was: stage II in 11.5%, IIIA in 23.1%, and IIIB in 65.4% of cases. The median time of relapse was 21 months from diagnosis (range: 10 to 42 months). The disease sites at relapse were multiple in 23 patients (88.46%) [including central nervous system (CNS) relapse in 3 patients) and CNS (brain) only in 3 patients (11.54%). The mutations detected included H1047R (3140A>G at exon 20) in 8 cases, E545K (1633 G>A at exon 9) in 5 cases, Q546R (1637 A>G at exon 9) in 4 cases, E542K (1624 G>A at exon7) in 3 cases and synchronous mutations (E542K/E545K at Exon 7) in 3 cases and (H1047R/H1047L at exon 20 ) in 3 cases. Only eight patients received alpelisib with fulvestrant due to financial constraints. Conclusions: This is the first Indian study that describes the prevalence of PIK3CA mutations in hormone-positive breast cancer at relapse. Around one-third of patients harbor this mutation and 23.1% of cases have CNS involvement at relapse. The most common PIK3CA mutation detected was H1047R (exon 20) followed by E545K (exon 9).

Association between PIK3CA mutations and disease-free survival in patients with HR+, HER2- tumors treated with adjuvant hormonal therapy: A real-world study in Croatia.

e12512 Background: Disease recurrence of early hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) breast tumor subtype is particularly challenging to manage due to its complex and very heterogeneous biological nature. Namely, due to primary and secondary resistance, one-quarter of patients with early disease will present with the disease recurrence. This variability in the timing of recurrence highlights the need to better identify key biomarkers that could predict therapeutic outcomes and guide personalized treatment strategies for these patients. Mutations in the phosphatidylinositol 4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) gene have a high prevalence of 30% to 40% in HR+/HER2- advanced breast cancer. They lead to activation of the PI3K/AKT/mTOR pathway, promoting cell growth, and proliferation, and are associated with poor prognosis in advanced breast cancer. Our aim was to examine this association and impact of PIK3CA mutation status on disease free survival (DFS) in HR+/ HER2- early breast cancer patients. Methods: We conducted a multicentric, retrospective cohort study in five Croatian institutions from July 2020 to December 2021. Study included initially early HR+/HER2- breast cancer patients who have been diagnosed with disease recurrence during adjuvant hormonal treatment or within first six years of follow up. The Cobas PIK3CA Mutation Testing Kit was used for real-time PCR-based amplification and mutation detection on the Cobas z 480 analyzer. We have analyzed differences in DFS from initiation of adjuvant endocrine therapy, using Cox, proportional hazard regression. Results: There was total of 186 patients, out of which 40.9% tested positive for the PIK3CA mutation. Primary and adjuvant treatment and in particular adjuvant endocrine treatment was similar between the two groups. After adjustment for 14 relevant covariates, we found that patients with positive PIK3CA status and with H1047 PIK3CA mutation had significantly lower hazard for disease recurrence in comparison to patients with no PIK3CA mutation (HR 0.65; 95% CI 0.45; 0.95; p = 0.024; HR 6.52; 95% CI 1.15; 36.95; p = 0.034 respectively; false discovery rate, FDR < 10%) and higher odds for late recurrence (p = 0.001, FDR < 5%). Conclusions: This study highlights the potential impact of PIK3CA mutations on disease recurrence during/following adjuvant endocrine treatment and by that potentially opens the door for further investigation of possibly more personalized treatment strategies.

Abstract 2407: Detection of hotspot PIK3CA mutations in primary tumors and plasma-cfDNA of breast cancer patients using a novel highly sensitive CE-IVD kit

Abstract Introduction: Detection of PIK3CA mutations in primary tumors (FFPEs) and liquid biopsy samples is of increasing importance for treatment decisions in breast cancer. Oncolipsy PIK3CA kit (Pharmassist Ltd, Greece) is based on the combination of allele-specific priming, asymmetric PCR, and melting curve analysis. The CE-IVD kit can detect the presence of four PIK3CA hotspot mutations (E542K, E545K, E545Q, H1047R). The aim of the present study was to: a) evaluate the performance of this novel CE-IVD kit both in FFPEs and plasma-cfDNA samples from patients with metastatic breast cancer (MBC) and b) directly compare the derived results using the Oncolipsy PIK3CA kit with the cobas® PIK3CA mutation test (CE-IVD, Roche Diagnostics, Germany) in identical gDNAs isolated from FFPEs samples. Patients and methods: We analyzed 42 primary tumors (FFPEs) and 29 plasma-cfDNA samples from patients with estrogen receptor (ER) positive metastatic breast cancer. Genomic DNA was isolated from FFPEs using the QIAamp DNA FFPE Tissue Kit (Qiagen, Hilden, Germany), while cfDNA was extracted from 2.00 mL of plasma using the QIAamp DSP cNA Kit (Qiagen, Hilden, Germany). PIK3CA hotspot mutations were detected in the LightCycler® 2.0 (IVD instrument, Roche Diagnostics, Germany) using the highly sensitive Oncolipsy PIK3CA kit (analytical sensitivity 0.05%). A direct comparison study was performed using the cobas® PIK3CA Mutation Test on the cobas z 480 analyzer (IVD instrument, Roche Diagnostics, Germany). Results: In primary tumors the E545K mutation was detected in 22/42 (52.4%), the E542K and H1047R mutations were detected in 11/42 (26.2%) and 4/42 (9.5%) of primary tumor samples, respectively, while the E545Q mutation was not detected in any FFPE sample tested. At least one PIK3CA mutation was detected in 14/29 (48.3%) plasma-cfDNA samples. More specifically the E545K mutation was detected in 11/29 (38%), the H1047R mutation in 3/29 (10.4%) and the E542K mutation in 2/29 (6.9%) while the E545Q mutation was not detected in any plasma-cfDNA sample tested. In FFPEs, as expected, PIK3CA mutation frequency was higher compared to plasma-cfDNA. Direct comparison of the results derived using these two commercially available kits, the Oncolipsy CE-IVD kit and the cobas PIK3CA mutation test, using the same gDNA isolated from 42 FFPEs revealed a concordance of 34/42 (81%). Conclusions: The commercially available Oncolipsy PIK3CA CE-IVD kit is highly sensitive and specific for the detection of four PIK3CA hotspot mutations in primary tumors and plasma-cfDNA. Acknowledgement: This study has been financially supported by the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH - CREATE - INNOVATE (project code: T1RCI-02935). Citation Format: Stavroula Smilkou, Dimitra Stergiopoulou, Eleni Tzanikou, Loukas Kaklamanis, Ioanna Balgkouranidou, Helena Linardou, Flora Zagouri, Evangelia Razi, Stylianos Kakolyris, Amanda Psyrri, Christos Papadimitriou, Ioanna Koukli, Athina Markou, Evi Lianidou. Detection of hotspot PIK3CA mutations in primary tumors and plasma-cfDNA of breast cancer patients using a novel highly sensitive CE-IVD kit [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2407.

Characterization of PIK3CA mutation testing in metastatic breast adenocarcinomas: a multi-site, single institution study

Abstract Introduction Detection of somatic mutations in advanced breast cancer may inform prognosis and therapy for patients. In ER+ breast cancer, nearly 40% of tumors have activating mutations in PI3 kinase (PIK3CA) for which targeted PI3 kinase inhibitors are available. At our institution, reflex ordered testing of PIK3CA in ER-positive, HER2-negative advanced breast cancers was implemented in 2017 to standardize the molecular biomarker testing in these tumors. Methods We analyzed 219 cases of advanced breast carcinoma diagnosed from 1/1/2017 to 12/31/2022 across the Houston Methodist system. With IRB approval, records were collated through full-text searching of interpretation, comment, and tumor synoptic fields in the anatomic pathology (AP) reports for “breast” and keywords for molecular oncologic testing, including “PIK3CA” and “MOLECULAR DIAGNOSTICS”, and then manually reviewed to exclude indeterminate/undifferentiated carcinomas and carcinomas of non-breast sites. Only molecular tests performed within this timeframe were considered. PIK3CA testing, both single-gene and targeted panels, was performed in 179 cases. Turnaround time (TAT) statistics, defined as days from AP report signout to molecular signout, were available for 102 cases. Cases with TATs greater than 60 days and referral laboratory testing were excluded. Data extraction, transformation, and loading was performed in Microsoft SQL Server (SSMS 18.0) and VS Code (Python 3.6). Analysis was performed using R-4.2.1 and Microsoft Excel. Results PIK3CA mutation testing was performed in 179 of 219 (82%) cases of all specimen types. The most common reasons for lack of reflex ordered molecular testing included insufficient tissue quantity and specimen decalcification. At least one PIK3CA genomic alteration was detected in 57 of 179 (32%) of cases. The most common alterations included p.H1047R (23/179, 13%), p.E545K (18/179, 10%), and p.E542K (8/179, 4%). One case had PIK3CA amplification, and one case had co-mutations of PIK3CA (p.G106V, p.H1047R). 217/219 (99%) of patients were female; no PIK3CA alterations were identified in the 2 male patients. PIK3CA frequency was not associated with age (mean age 65.4 for PIK3CA alteration detected and 63.8 for not detected, p=0.41). Mean TAT was 16.4 days (n=102), and 56% (57/102) of cases were resulted within 2 weeks of AP reporting. 22% (40/179) of cases had PIK3CA performed at a referral laboratory, largely occurring during the COVID-19 pandemic. Conclusion A reflex ordered strategy for PIK3CA mutations in advanced breast cancers led to the prompt availability of appropriate molecular results for most patients. PIK3CA alterations were present in 32% of cases, with the most common mutations being p.H1047R, p.E545K, and p.E542K. No significant differences in PIK3CA alterations by patient age was observed. Some cases had extended TATs for molecular results, which may be due to ordering practices, the specific PIK3CA testing procedure, and test send-out. Further studies will investigate the association of PIK3CA mutations and clinical staging.

Rezultati multicentričnog testiranja somatskih mutacija gena PIK3CA kod uznapredovalog luminalnog raka dojke s negativnim HER2 receptorom

Aim: Activating somatic mutations in p110α catalytic subunit of PIK3-kinase (PIK3CA) are present in about 40% of breast cancers (BC), and are involved in oncogenesis and cancer growth. PIK3CA inhibitor therapy is approved for patients with advanced HR+/HER2- endocrine-resistant BC with somatic PIK3CA mutations. Such targeted therapy improved patient disease-free survival. Method: Analyses of PIK3CA gene mutations were performed in five University Hospital Centers in Croatia. Qualitative detection of PIK3CA gene mutations was performed on DNA extracted from 507 breast cancer samples, by the real-time PCR method using Cobas® PIK3CA mutation test. Results: PIK3CA gene mutations were detected in 209 (42.2%) out of 495 successfully analyzed cases. In 12 cases (2.4%), the tumor tissue was not of sufficient quality for analysis. Most mutations were detected in the helical (41.2%) and kinase domains (46.9%) of the PIK3CA protein. The most frequently detected mutations were H1047L/R/Y (46.4%), E545A/D/G/K (26.3%) and E542K (13.9%), followed by N345K (8.1%). PIK3CA mutations were detected in 44.8% of primary BC cases and in 39.6% of metastatic lesions (χ2=0.647; P=0.421). The age of the tissue did not significantly affect the percentage of detected mutations (χ2=0.543; P =0.461). Institutions differed in the number of analyzed cases, but not in the percentage of detected PIK3CA mutations (χ2=6.23; df=4; P=0.183) nor in the frequency of the most common mutations (χ2=2.65; df=4; P=0.618). Conclusion: The frequencies of PIK3CA mutations correspond to those reported in the literature. We have shown that the tissue of primary BC as well as metastatic lesions are suitable for analysis, and that the age of the tissue is not a significant obstacle in the analysis.

PIK3CA mutation testing as a valuable molecular surrogate for lipomatosis of the median nerve: clinicopathological and molecular analysis of six cases

Lipomatosis of peripheral nerves (LPN, also known as fibrolipomatous or lipofibromatous hamartoma of peripheral nerves) is a very rare, benign, intraneural, tumorous lesion that predominantly involves the median nerve but may rarely affect any peripheral nerve. Recently, PIK3CA mutations have been reported in macrodactyly, a rare condition related to LPN, and in other localized lipomatous overgrowth syndromes. In this retrospective study, we report 6 cases of FPN involving the median nerve (4 of them identified among 570 patients with carpal tunnel syndrome who underwent surgical decompression at our center from 2012 to 2022 and two seen in consultation by one of the authors). All cases were diagnosed via biopsy or resection supplemented by MRI. Patients were 4 males and 2 females aged 23 to 60 years (mean 38 years). One patient with bilateral lesions had in addition extensive angiomatosis of the paravertebral region. Histological examination showed an abnormal amount of mature fatty tissue containing disordered fibrous bands, entrapping normal-looking nerve fibers with prominent perineurial and endoneurial fibrosis. Genetic analysis using snapshot assay constructed to detect hotspots mutations in PIK3CA revealed similar PIK3CA mutations (p.H1047R; c.3140A>G) in 5/6 cases (83.3%). Our study represents a further contribution to the literature on LPN and highlights the diagnostic value of PIK3CA mutation testing as surrogate tool in equivocal cases and in those lesions without associated macrodactyly, especially as the biopsy findings of this lesion are essentially nonspecific.

Evaluation of PIK3CA mutations in advanced ER+/HER2-breast cancer in Portugal - U-PIK Project.

Background: Around 40% of ER+/HER2-breast carcinomas (BC) present mutations in the PIK3CA gene. Assessment of PIK3CA mutational status is required to identify patients eligible for treatment with PI3Kα inhibitors, with alpelisib currently the only approved tyrosine kinase inhibitor in this setting. U-PIK project aimed to conduct a ring trial to validate and implement the PIK3CA mutation testing in several Portuguese centers, decentralizing it and optimizing its quality at national level. Methods: Eight Tester centers selected two samples of patients with advanced ER+/HER2- BC and generated eight replicates of each (n = 16). PIK3CA mutational status was assessed in two rounds. Six centers used the cobas® PIK3CA mutation test, and two used PCR and Sanger sequencing. In parallel, two reference centers (IPATIMUP and the Portuguese Institute of Oncology [IPO]-Porto) performed PIK3CA mutation testing by NGS in the two rounds. The quality of molecular reports describing the results was also assessed. Testing results and molecular reports were received and analyzed by U-PIK coordinators: IPATIMUP, IPO-Porto, and IPO-Lisboa. Results: Overall, five centers achieved a concordance rate with NGS results (allele frequency [AF] ≥5%) of 100%, one of 94%, one of 93%, and one of 87.5%, considering the overall performance in the two testing rounds. NGS reassessment of discrepancies in the results of the methods used by the Tester centers and the reference centers identified one probable false positive and two mutations with low AF (1-3%, at the analytical sensitivity threshold), interpreted as subclonal variants with heterogeneous representation in the tissue sections processed by the respective centers. The analysis of molecular reports revealed the need to implement the use of appropriate sequence variant nomenclature with the identification of reference sequences (HGVS-nomenclature) and to state the tumor cell content in each sample. Conclusion: The concordance rates between the method used by each tester center and NGS validate the use of the PIK3CA mutational status test performed at these centers in clinical practice in patients with advanced ER+/HER2- BC.

Analysis of PIK3CA Mutation Concordance and Frequency in Primary and Different Distant Metastatic Sites in Breast Cancer.

The purpose of this study was to investigate the concordance rate of PIK3CA mutations between primary and matched distant metastatic sites in patients with breast cancer and to verify whether there are differences in the frequency of PIK3CA hotspot mutations depending on the metastatic sites involved. Archived formalin-fixed paraffin-embedded (FFPE) specimens of primary breast and matched distant metastatic tumors were retrospectively obtained for 49 patients. Additionally, 40 archived FFPE specimens were independently collected from different breast cancer metastatic sites, which were limited to three common sites: the liver, brain, and lung. PIK3CA mutations were analyzed using droplet digital PCR, including hotspots involving exons 9 and 20. After analysis of 49 breast tumors with matched metastasis sites, 87.8% showed concordance in PIK3CA mutation status. According to PIK3CA hotspot mutation testing in 89 cases of breast cancer metastatic sites, the proportion of PIK3CA mutations at sites of metastasis involving the liver, brain, and lung was 37.5%, 28.6%, and 42.9%, respectively, which did not result in statistical significance. The high concordance of PIK3CA mutation status between primary and matched metastasis sites suggests that metastatic sites, regardless of the metastatic organ, could be considered sample sources for PIK3CA mutation testing for improved therapeutic strategies in patients with metastatic breast cancer.

Role of Alpelisib in the Treatment of PIK3CA-Mutated Breast Cancer: Patient Selection and Clinical Perspectives.

The PI3K/AKT/mTOR pathway has long been known to play a major role in the growth and survival of cancer cells. Breast tumors often harbor PIK3CA gene alterations, which therefore constitute a rational drug target. However, it has taken many years to demonstrate clinically-relevant efficacy of PI3K inhibition and eventually attain regulatory approvals. As data on PI3K inhibitors continue to mature, this review updates and summarizes the current state of the science, including the prognostic role of PIK3CA alterations in breast cancer; the evolution of PI3K inhibitors; the clinical utility of the first-in-class oral selective PI3Kα inhibitor, alpelisib; PIK3CA mutation detection techniques; and adverse effect management. PIK3CA-mutated breast carcinomas predict survival benefit from PI3K inhibitor therapy. The pan-PI3K inhibitor, buparlisib and the beta-isoform-sparing PI3K inhibitor, taselisib, met efficacy endpoints in clinical trials, but pictilisib did not; moreover, poor tolerability of these three drugs abrogated further clinical trials. Alpelisib is better tolerated, with a more manageable toxicity profile; the principal adverse events, hyperglycemia, rash and diarrhea, can be mitigated by intensive monitoring and timely intervention, thereby enabling patients to remain adherent to clinically beneficial treatment. Alpelisib plus endocrine therapy shows promising efficacy for treating postmenopausal women with HR+/HER2– advanced breast cancer. Available evidence supporting using alpelisib after disease progression on first-line endocrine therapy with or without CDK4/6 inhibitors justifies PIK3CA mutation testing upon diagnosing HR+/HER2– advanced breast cancer, which can be done using either tumor tissue or circulating tumor DNA. With appropriate toxicity management and patient selection using validated testing methods, all eligible patients can potentially benefit from this new treatment. Further clinical trials to assess combinations of hormone therapy with PI3K, AKT, mTOR, or CDK 4/6 inhibitors, or studies in men and women with other breast subtypes are ongoing.

Abstract PD2-06: Clinical outcomes of alpelisib plus fulvestrant in hormone receptor-positive, human epidermal growth factor receptor-2-negative advanced breast cancer with PIK3CA alterations detected in plasma ctDNA by next-generation sequencing: Biomarker analysis from the SOLAR-1 study

Abstract Introduction: The PI3K pathway is often hyperactivated in cancer as a result of an altered PI3K isoform and/or loss of phosphatase and tensin homolog function. Approximately 40% of patients (pts) with hormone receptor-positive (HR+), human epidermal growth factor receptor-2-negative (HER2−) advanced breast cancer (ABC) have tumors with mutations in PIK3CA, which encodes the α-isoform of PI3K, p110α. These mutations are known to cause hyperactivation of the PI3K pathway, which contributes to cell proliferation, drug resistance, and poor prognoses. Alpelisib (ALP) is an α-selective PI3K inhibitor that, in combination with fulvestrant (FUL), prolonged median progression-free survival (mPFS) in pts with HR+, HER2−, PIK3CA-mutant ABC following progression on/after prior aromatase inhibitor in the phase 3 SOLAR-1 trial. In SOLAR-1, prospective PIK3CA mutation testing was performed on tumor tissue using PCR-based assays. Through retrospective analysis, efficacy of ALP was demonstrated in subgroups of pts with PIK3CA alteration(s) in tumor tissue and mutation(s) in ctDNA, detected by next-generation sequencing (NGS) and PCR, respectively. In this exploratory biomarker analysis, we assessed clinical outcomes of pts with PIK3CA alteration(s), detected in ctDNA by NGS.Methods: SOLAR-1 is a phase 3, randomized, double-blind, placebo-controlled study of ALP 300 mg vs placebo taken daily with FUL 500 mg every 28 days + Cycle 1 Day 15 in men and postmenopausal women with HR+, HER2- ABC. Retrospectively, the full exonic region of the PIK3CA gene was sequenced using the Foundation Medicine 324-gene ctDNA panel in plasma ctDNA collected at baseline. mPFS was assessed using Kaplan-Meier methodology per investigator assessment.Results: Of 572 pts in SOLAR-1, 381 pts (66.6%) across both PIK3CA-mutant and nonmutant cohorts had valid plasma ctDNA data. Of these pts, 193 (50.7%) had a PIK3CA alteration; 168 (87%) had PCR-detectable mutations and 147 (76%) had a single alteration. A total of 70 (36%) and 102 (53%) pts had alterations in exons 9 and 20, respectively. ALP plus FUL prolonged mPFS in pts with PIK3CA alterations detected in plasma ctDNA by NGS (n=101; Table). Clinical benefit was also observed in pts with PCR-detectable mutations (n=88), single mutations (n=83), and pts with mutations in exon 9 (n=34) and exon 20 (n=54). Pt numbers were low, and wide 95% CIs were observed in groups with alterations not detectable by PCR (n=13) and in pts with multiple alterations. Some limitations of this retrospective plasma analysis include that this is a subgroup (66.6%) of the SOLAR-1 pt population and that the subgroup of pts with non-altered PIK3CA included pts with a PIK3CA mutation in their tumor tissue. Conclusions: ALP plus FUL demonstrated clinical benefit in pts with PIK3CA mutations detected in plasma ctDNA by NGS, in pts with single alterations, and in pts with alterations in exons 9 and 20. Results were consistent across pt groups, except in those with alterations not detectable by PCR. In conclusion, these data demonstrate a consistent clinical benefit of ALP plus FUL in various groups of pts with PIK3CA alterations detected in ctDNA by NGS. Clinical Outcomes of Patients With PIK3CA Alterations Detected in Plasma ctDNA by NGS in SOLAR-1Alpelisib + fulvestrantPlacebo + fulvestrantHR (95% CI)Events/N (%)mPFS, mo (95% CI)Events/N(%)mPFS, mo (95% CI)PIK3CA altered vs non-alteredAltered58/101(57.4)11.04(7.72-16.16)73/92(79.3)3.65(2.86-6.80)0.47(0.33-0.67)Non-altered40/87(46.0)10.87(5.59-16.76)60/101(59.4)5.45(3.75-9.00)0.60(0.40-0.91)PIK3CA: alteration detectable by PCR vs alteration not detectable by PCRDetectable52/88(59.1)12.48(7.36-18.37)66/80(82.5)3.58(2.37-5.65)0.44(0.30-0.64)Not detectable6/13(46.2)8.48(2.69-NA)7/12(58.3)7.39(1.87-12.98)1.12(0.35-3.56)PIK3CA: number of alterationsSingle45/83(54.2)12.88(7.36-18.50)50/64(78.1)3.58(1.87-6.11)0.43(0.28-0.65)Multiple13/18(72.2)9.00(3.68-18.37)23/28(82.1)4.63(3.48-9.63)0.55(0.25-1.20)PIK3CA alterations in exon 9 or exon 20Exon 918/34(52.9)15.21(7.03-NA)29/36(80.6)3.66(2.86-7.36)0.31(0.16-0.61)Exon 2034/54(63.0)10.91(5.72-18.37)40/48(83.3)3.52(1.87-6.11)0.51(0.31-0.82)CI, confidence interval; ctDNA, circulating tumor DNA; HR, hazard ratio; mPFS, median progression-free survival; mo, months; NA, not available; NGS, next-generation sequencing. Citation Format: Eva M. Ciruelos, Sibylle Loibl, Ingrid A. Mayer, Mario Campone, Hope S. Rugo, Monica Arnedos, Hiroji Iwata, Pier Franco Conte, Fabrice André, Albert Reising, Chong Ma, Michelle Miller, Naveen Babbar, Dejan Juric. Clinical outcomes of alpelisib plus fulvestrant in hormone receptor-positive, human epidermal growth factor receptor-2-negative advanced breast cancer with PIK3CA alterations detected in plasma ctDNA by next-generation sequencing: Biomarker analysis from the SOLAR-1 study [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD2-06.

Phase III randomized study of taselisib or placebo with fulvestrant in estrogen receptor-positive, PIK3CA-mutant, HER2-negative, advanced breast cancer: the SANDPIPER trial

The phase III SANDPIPER study assessed taselisib (GDC-0032), a potent, selective PI3K inhibitor, plus fulvestrant in estrogen receptor-positive, HER2-negative, PIK3CA-mutant locally advanced or metastatic breast cancer. Postmenopausal women with disease recurrence/progression during/after an aromatase inhibitor were randomized 2 : 1 to receive taselisib (4 mg; taselisib arm) or placebo (placebo arm) plus fulvestrant (500 mg). Stratification factors were visceral disease, endocrine sensitivity, and geographic region. Patients with PIK3CA-mutant tumors (central cobas® PIK3CA Mutation Test) were randomized separately from those without detectable mutations. The primary endpoint was investigator-assessed progression-free survival (INV-PFS) in patients with PIK3CA-mutant tumors. Secondary endpoints included objective response rate, overall survival, clinical benefit rate, duration of objective response, PFS by blinded independent central review (BICR-PFS), safety, and time to deterioration in health-related quality of life. The PIK3CA-mutant intention-to-treat population comprised 516 patients (placebo arm: n= 176; taselisib arm: n= 340). INV-PFS was significantly improved in the taselisib {7.4 months [95% confidence interval (CI), 7.26-9.07]} versus placebo arm (5.4 months [95% CI, 3.68-7.29]) (stratified hazard ratio [HR] 0.70; 95% CI, 0.56-0.89; P= 0.0037) and confirmed by BICR-PFS (HR 0.66). Secondary endpoints, including objective response rate, clinical benefit rate, and duration of objective response, showed consistent improvements in the taselisib arm. Safety was assessed in all randomized patients who received at least one dose of taselisib/placebo or fulvestrant regardless of PIK3CA-mutation status (n= 629). Serious adverse events were lower in the placebo versus taselisib arm (8.9% versus 32.0%). There were more discontinuations (placebo arm: 2.3%; taselisib arm: 16.8%) and dose reductions (placebo arm: 2.3%; taselisib arm: 36.5%) in the taselisib arm. SANDPIPER met its primary endpoint; however, the combination of taselisib plus fulvestrant has no clinical utility given its safety profile and modest clinical benefit.

Plasma PIK3CA Mutation Testing in Advanced Breast Cancer Patients for Personalized Medicine: A Value Proposition.

Even though endocrine therapy is often initially successful in treating advanced breast cancer, most patients inevitably face disease progression. In advanced hormone receptor-positive (HR+) breast cancer, activation of the PI3K downstream pathway is a critical feature of the mechanism of endocrine resistance. A significant recent advance in treating HR+ advanced breast cancer has been the recent introduction of PI3K inhibitor (PI3Ki) for the treatment of patients with HR+, HER2-negative (HER2-) advanced or metastatic breast cancer that harbors PIK3CA mutations. A value proposition concept was applied to assess the potential benefits of cell-free tumor DNA (ctDNA) testing to identify patients who might respond to PI3Ki treatment. By applying the framework of the value proposition to >35 publications, in addition to recommendations from professional organizations, it was evident that robust clinical evidence exists to support the role of ctDNA PIK3CA mutation evaluation in identifying patients with advanced breast cancer who could benefit from PI3Ki treatment. Detection of PIK3CA gene mutations in HR+HER2- advanced breast cancer patients allows for the identification of patients who might benefit from more effective personalized treatment with molecularly targeted drugs.

A Systematic Review of the Prevalence and Diagnostic Workup of PIK3CA Mutations in HR+/HER2- Metastatic Breast Cancer.

PIK3CA mutation frequency varies among breast cancer (BC) subtypes. Recent evidence suggests combination therapy with the PI3K inhibitor (PI3Ki) alpelisib and endocrine therapy (ET) improves response rates and progression-free survival (PFS) in PIK3CA-mutant, hormone receptor positive (HR+) BC versus ET alone; thus, better understanding the clinical and epidemiologic elements of these mutations is warranted. This systematic review characterizes the PIK3CA mutation epidemiology, type of testing approaches (e.g., liquid or tissue tumor biopsy), and stability/concordance (e.g., consistency in results by liquid versus solid tumor sample, by the same method over time) in patients with HR+/HER2– advanced (locally unresectable) or metastatic disease (HR+/HER2– mBC) and explores performance (e.g., pairwise concordance, sensitivity, specificity, or predictive value) of respective mutation findings. A comprehensive search of PubMed/MEDLINE, EMBASE, Cochrane Central, and select conference abstracts (i.e., AACR, ASCO, SABCS, ECCO, and ESMO conferences between 2014 and 2017) identified 39 studies of patients with HR+, HER2– mBC. The median prevalence of PIK3CA mutation was 36% (range: 13.3% to 61.5%); identified testing approaches more commonly used tissue over liquid biopsies and primarily utilized next-generation sequencing (NGS), polymerase chain reaction (PCR), or Sanger sequencing. There was concordance and stability between tissues (range: 70.4% to 94%) based on limited data. Given the clinical benefit of the PI3Ki alpelisib in patients with PIK3CA mutant HR+/HER2– mBC, determination of tumor PIK3CA mutation status is of importance in managing patients with HR+/HER2– mBC. Prevalence of this mutation and utility of test methodologies likely warrants PIK3CA mutation testing in all patients with this breast cancer subtype via definitive assessment of PIK3CA mutational status.

Abstract P4-10-04: Clinical outcomes of alpelisib in hormone receptor-positive, human epidermal growth factor receptor-2-negative advanced breast cancer by next-generation sequencing-detected PIK3CA alteration status and phosphatase and tensin homolog loss: Biomarker analysis from the SOLAR-1 study

Introduction: Hyperactivation of the phosphoinositide-3-kinase (PI3K) pathway is a frequent event in human cancers and can be a result of phosphatase and tensin homolog (PTEN) loss, activation of receptor tyrosine kinases, or alterations in PI3K isoforms. About 40% of hormone receptor-positive (HR+), human epidermal growth factor receptor-2-negative (HER2-) breast cancers harbor alterations in the PIK3CA gene, which encodes the alpha subunit of PI3K (p110α). Mutations in PIK3CA can cause PI3K pathway hyperactivation, which may contribute to endocrine resistance. Alpelisib (ALP) is an α-selective PI3K inhibitor that, in combination with fulvestrant (FUL), demonstrated improved median progression-free survival (PFS) vs placebo (PBO) + FUL (11.0 vs 5.7 mo, respectively; hazard ratio [HR] 0.65; 95% confidence interval [CI], 0.50-0.85; P Methods: SOLAR-1 is a phase 3, randomized, double-blind study of ALP 300 mg (or PBO) once daily + FUL 500 mg every 28 days + Cycle 1 Day 15 in men and postmenopausal women with HR+, HER2- ABC. Retrospectively, PIK3CA alterations (mutations and amplifications) were assessed by NGS and PTEN levels were assessed by immunohistochemistry. PTEN loss was defined based on an H-score Results: Of 572 pts in SOLAR-1, 341 (60%) had a PIK3CA mutation in tumor tissue by PCR, valid NGS results were available for 404 (71%), and PTEN levels were available for 401 (70%). Of the pts with available PTEN results, 34 (8%) had PTEN loss. PFS results and HRs, by PIK3CA alteration status as detected by NGS and PTEN status, are shown in the Table. In pts whose tumors had any PIK3CA alteration (n=239), which included a small group of pts with alterations not detectable by the PCR-based test used for screening in SOLAR-1 (n=31), mPFS was improved in the ALP + FUL vs PBO + FUL arms. In the small group of pts (n=19) whose tumors had PTEN loss but no PIK3CA alteration, ALP showed an improved mPFS and favorable HR vs the placebo arm. In pts whose tumors had multiple alterations (n=44), HR and mPFS benefits of ALP were observed, albeit with wide 95% CIs. Conclusions: These data demonstrate the efficacy of ALP in pts whose tumors harbor PIK3CA alterations as detected by NGS, including alterations that were not detectable by the PCR-based test used in SOLAR-1. Additional analyses suggest that ALP is also effective in pts with single and multiple PIK3CA mutations and in those whose tumors do not harbor a PIK3CA alteration but do have PTEN loss; however, low patient numbers in the PTEN loss subgroups may limit conclusions. Citation Format: Dejan Juric, Fabrice Andre, Christian F. Singer, Joohyuk Sohn, Mario Campone, Sibylle Loibl, Pierfranco Conte, Hiroji Iwata, Eva Ciruelos, Ingrid A. Mayer, Albert Reising, Chong Ma, Michelle Miller, Naveen Babbar, Hope S. Rugo. Clinical outcomes of alpelisib in hormone receptor-positive, human epidermal growth factor receptor-2-negative advanced breast cancer by next-generation sequencing-detected PIK3CA alteration status and phosphatase and tensin homolog loss: Biomarker analysis from the SOLAR-1 study [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-10-04.

Abstract P1-18-18: PIK3CA mutation testing prevalence among post-menopausal (PM) women with hormone receptor positive and human epidermal growth factor receptor 2 negative (HR+/HER2-) metastatic breast cancer (mBC) using real world data

Abstract Background: Mutation testing has historically been of limited utility in patients with mBC due to the absence of approved treatments directed at specific genetic variants. However, the SOLAR-1 trial found improved progression-free survival with the addition of the PI3K inhibitor, alpelisib, to fulvestrant, versus placebo, among patients with PIK3CA mutated HR+/HER2- mBC, leading to FDA approval of alpelisib and indicating that PIK3CA mutation assessment has significant clinical relevance. The FDA approval for alpelisib after progression on endocrine therapy necessitates that PIK3CA status be ascertained relatively early in the course of disease of patients with HR+/HER2- mBC. We therefore examined the prevalence and timepoint of mutation testing encompassing PIK3CA among PM women with HR+/HER2- mBC in the United States (US). Methods: This retrospective cohort study used administrative claims data from the MarketScan Commercial and Medicare Supplemental Databases, which include longitudinal records of medical services and prescription drugs from 25-30 million employees and dependents annually, covered by a variety of health plans. PM women diagnosed with mBC between 1/1/2012-7/31/2018 (index date = first metastasis diagnosis date) were selected. Patients were required to have HR+/HER2- disease defined by at least one prescription for endocrine therapy and no evidence of anti-HER2 targeted therapy post-index. The follow-up period was from index until inpatient death, disenrollment, or study end. Mutation testing was captured by a Current Procedural Terminology (CPT) code (81404, 81455, 81445) for polymerase chain reaction (PCR) or next generation sequencing (NGS) inclusive of PIK3CA mutation during the study period. The provider type on the BC-related outpatient physician office visit closest to the first mutation testing date was identified. Testing prevalence was calculated as percent of eligible PM women with HR+/HER2- mBC with a procedure code for PCR and/or NGS test. Results: The study population included 8,499 mBC patients with mean (standard deviation [SD]) age 66.5 (10.6) years and an average follow-up duration of 1.9 (1.4) years. In total, 177 (2.1%) patients had NGS or PCR inclusive of the PIK3CA test during the study period. Of patients with a test, 28.8% (N=51) underwent testing prior to the start of first systemic therapy for metastatic disease (first line) and 126 (71.2%) were tested during or after first line (Table). Of patients with a test, 88.1% (N=156) had a BC-related outpatient physician office visit within 30 days prior to the test. The majority (55.1%) of visits (N=156) were with a hematologist-oncologist. N%All eligible PM women with HR+/HER2- mBC8,499Patients with PCR and NGS testing inclusive of PIK3CA mutation177 2.1%Timing of earliest test (among those with testing) Prior to distant metastasis2212.4%From date of distant metastasis to first line2916.4%During first line4726.6%After first line7944.6% Conclusions: Patients with HR+/HER2- mBC are infrequently tested for mutations such as PIK3CA, with majority of patients not being tested before the initiation of first line therapy. The demonstrated benefit of alpelisib in patients with PIK3CA mutations likely necessitates widespread testing for this important predictive factor early in the disease course. Future analyses are needed to determine the temporal trends over time and assess how genotype testing could be more standard. Citation Format: Nicole Princic, Qayyim Said, David Smith, William Johnson, Ayal Aizer. PIK3CA mutation testing prevalence among post-menopausal (PM) women with hormone receptor positive and human epidermal growth factor receptor 2 negative (HR+/HER2-) metastatic breast cancer (mBC) using real world data [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-18-18.

Abstract 3976: “Fit-for-purpose” PIK3CA assays for patient stratification in breast cancer clinical trials

Abstract Background: Prospective clinical trials stratifying by PIK3CA genotype is necessary to determine if the mutation predicts for increased sensitivity to agents targeting the phosphoinositide 3-kinase (PI3K) pathway. It is crucial to select appropriate assays to optimize operational, scientific and timeline requirements for patient enrollment in a real world setting. Here we report application of three different PIK3CA mutation test methods during the course of a PI3K TKI development. Methods: We customized Sanger sequencing, cobas® assay and a proprietary investigational use only (IUO) assay to detect point mutations in PIK3CA in order to accommodate the development needs at the different stages of clinical development of PIK3CA TKIs. We performed method comparison studies to determine the most cost effective and “fit-for-purpose” assay for clinical trial testing. Specimen requirements, assay performance characteristics, turnaround-time (TAT) and valid result rates were assessed to select the best test method for patient stratification to meet the requirements of each stage of drug development. Results: PIK3CA test results can be obtained from a single, 5μm FFPE section with ≥0.1% and ≥10% tumor in the IUO and cobas® tests respectively. Sanger Sequencing requires longer processing time and ≥30% tumor content. The cobas® assays were validated in FFPE samples and can reliably detect PIK3CA mutations in exons 9 and 20 with ≥5% mutation level. The method comparison study showed that the concordance rate between Sanger sequencing and cobas® PIK3CA assay is 86% among the 360 samples tested while it is 96% between the cobas® assay and the IUO assay among 395 samples tested. The IUO assay is slightly more sensitive, and calls out the exact mutation while the cobas® assay may not. The Sanger sequencing demonstrated the lowest sensitivity and required more DNA input, which resulted in more samples failing to yield a valid result. The cobas® assay is a more user-friendly assay allowing better laboratory efficiency and TAT. Patients selected using the IUO assay showed a median progression-free survival nearly twice as long among those receiving a PI3K TKI compared to placebo. Conclusions: The most important factor in selecting a testing platform for clinical trial patient stratification is the assay performance characteristics. We employed the Sanger sequencing assay in the initial trial testing, then switched to the cobas® assay, and finally to the IUO assay to meet the requirements as the drug progressed through different stages of clinical development. The IUO assay has the performance characteristics that meet the regulatory requirements and a validated clinical utility in selecting patients for PI3K TKI treatment, thus on its way to a companion diagnostic submission. Citation Format: Hua C. Gong, Sharmila Manjeshwar, Violet Abraham, Shawn Rivera. “Fit-for-purpose” PIK3CA assays for patient stratification in breast cancer clinical trials [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3976.

Targeted Therapy in Metastatic Colorectal Cancer: Current Standards and Novel Agents in Review.

Treatment options for patients with metastatic colorectal cancer continue to advance as the therapeutic implications of the molecular subtypes of this disease are becoming better understood. DNA sequencing and mismatch repair assessment are now standard of care analyses for patients with metastatic colorectal cancer Thi review describes important aspects of the biology of the clinically relevant molecular subtypes of colorectal cancer based on the current standard of care testing. In addition, the clinical treatment strategies available now and potentially in the future for these colorectal cancer subtypes are discussed. Currently for metastatic colorectal cancer, standard of care molecular testing is done for mutations in exons 2, 3, and 4 of KRAS and NRAS, and BRAF V600E. Testing for mismatch repair (MMR) deficiency/microsatellite instability (MSI) status is also done. These aberrations are well known to change the clinical prognosis and guide patients' treatment strategies. Additionally, three new subtypes have emerged: PIK3CAmut, HER2 amplified, and NTRK fusions. With the addition of these emerging subtypes, tumor heterogeneity further validates the need to examine mCRC as a heterogeneous disease. Here we present recent exciting data from translational research and clinical trials exhibiting possible distinct treatment strategies for these different subtypes. Altogether these data show promising treatment strategies for many of these well-known and emerging subtypes of mCRC. In addition, these also give better clinical prognostic and predictive information. We believe that as molecular testing expands PIK3CA mutation, HER2 amplification, and NTRK fusion molecular testing will be included in standard of care analyses. This incorporation of testing in clinical practice will generate further information regarding prognostic and therapeutic options for these and other CRC subtypes in the future.

Exploring Biomarkers of Phosphoinositide 3-Kinase Pathway Activation in the Treatment of Hormone Receptor Positive, Human Epidermal Growth Receptor 2 Negative Advanced Breast Cancer.

Resistance to endocrine therapy (ET) is common in patients with hormone receptor positive (HR+) advanced breast cancer (ABC). Consequently, new targeted treatment options are needed in the post-ET setting, with validated biomarkers to inform treatment decisions. Hyperactivation of the phosphoinositide 3-kinase (PI3K) signaling pathway is common in ABC and is implicated in resistance to ET. The most frequent mechanism of PI3K pathway activation is activating mutations or amplification of PIK3CA, which encodes the α-isoform of the catalytic subunit of PI3K. Combining buparlisib, a pan-PI3K-targeted agent, with ET demonstrated modest clinical benefits in patients with aromatase inhibitor-resistant, HR+, human epidermal growth receptor 2 negative (HER2-) ABC in two phase III trials. Importantly, greater efficacy gains were observed in individuals with PIK3CA-mutated disease versus PIK3CA-wild-type tumors. Although the challenging safety profile did not support widespread use of this treatment combination, isoform-selective PI3K inhibitors may improve tolerability. In early clinical trials, promising disease control benefits were demonstrated with the PI3K isoform-selective inhibitors alpelisib and taselisib in patients with PIK3CA-mutated HR+, HER2- ABC. Ongoing biomarker-guided phase II/III studies may provide further opportunities to identify patients most likely to benefit from treatment with PI3K inhibitors and provide insight into optimizing the therapeutic index of PI3K inhibitors. Challenges facing the implementation of routine PIK3CA mutation testing must be addressed promptly so robust and reproducible genotyping can be obtained with liquid and tumor biopsies in a timely and cost-effective manner. IMPLICATIONS FOR PRACTICE: The development of phosphoinositide 3-kinase (PI3K) inhibitors, especially those that selectively target isoforms, may be an effective strategy for overcoming endocrine therapy resistance in hormone receptor positive, human epidermal growth receptor 2 negative advanced breast cancer. Early-phase studies have confirmed that patients with PIK3CA mutations respond best to PI3Kα-isoform inhibition. Ongoing phase III trials will provide further data regarding the efficacy and safety of PI3K inhibitors in patients with different biomarker profiles.