Abstract CT046: A phase I basket study of the PI3K inhibitor taselisib (GDC-0032) in PIK3CA-mutated locally advanced or metastatic solid tumors

Background: PIK3CA , a gene that encodes the α-isoform of the catalytic subunit of Class I PI3K (PI3Kα), is frequently mutated or amplified in solid tumors. Taselisib is an oral, potent, selective inhibitor of Class I PI3Kα, γ, and δ isoforms with enhanced activity against PIK3CA -mutated cancer models. Preclinical and clinical data demonstrated that single-agent taselisib has activity in multiple PIK3CA -mutated tumor types. Methods: This open-label phase I study (Cohort X of PMT4979g; NCT01296555) enrolled patients (pts) with PIK3CA -mutated tumors who had progressed after, or failed to respond to, at least one prior treatment regimen and were not candidates for regimens known to provide clinical benefit. Pts received single-agent taselisib (4 or 6 mg tablet, daily). Eleven subcohorts comprised various solid tumor types: endometrial, bladder, head and neck squamous cell carcinoma (HNSCC), cervical, gastric/gastroesophageal junction, small cell lung, triple-negative breast, colorectal (excluding KRAS -mutated tumors), squamous (excluding histologies in the other subcohorts), ovarian, and pts with PIK3CA mutant tumors not otherwise specified (excluding breast, colorectal, and non-small-cell lung cancers). Tumor tissue (archival or fresh) was assessed centrally for PIK3CA mutation or amplification. The primary endpoint was tolerability and safety of taselisib. Other endpoints included assessment of antitumor activity per Response Evaluation Criteria In Solid Tumors (RECIST) v1.1. Results: At data cutoff (May 1, 2017), 146 pts have been enrolled. Overall, the most common adverse events (AEs; ≥30% of pts) were diarrhea (58.2%), nausea (39.0%), hyperglycemia (31.5%), and fatigue (30.8%). Ninety-four pts (64.4%) experienced ≥1 grade ≥3 AE and 53 pts (36.3%) had grade ≥3 AEs related to taselisib. Sixty-eight pts (46.6%) had serious AEs (SAEs) and the most common SAEs (>2 pts) related to taselisib treatment were colitis (5.5%), diarrhea (4.1%), and hyperglycemia (3.4%). Nine pts (6.2%) had grade 5 events; one AE with a fatal outcome (0.7%) was assessed by the investigator as related to taselisib (septic shock). AEs that led to dose reduction, interruption, or withdrawal were reported in 34 pts (23.3%), 59 pts (40.4%), and 14 pts (9.6%), respectively. Overall, confirmed response rates were 8.9% (n=13) and clinical benefit rates (confirmed response or without disease progression for ≥6 months) were 12.3% (n=18). Confirmed responses were observed in pts with endometrial cancer (2/10 [20.0%]), HNSCC (4/21 [19.0%]), and cervical cancer (2/19 [10.5%]), as well as other tumor types. Conclusions: Single-agent taselisib had an acceptable safety profile (with AEs that were generally reversible and manageable; no new safety signals were identified) and preliminary clinical activity in pts with PIK3CA -mutated locally advanced or metastatic solid tumors. Citation Format: Komal Jhaveri, Dejan Juric, Cristina Saura, Andres Cervantes, Anton Melnyk, Manish R. Patel, Mafalda Oliveira, Valentina Gambardella, Vincent Ribrag, Cynthia X. Ma, Raid Aljumaily, Philippe L. Bedard, Jasgit C. Sachdev, John Bond, Surai Jones, Timothy R. Wilson, Michael C. Wei, Jose Baselga. A phase I basket study of the PI3K inhibitor taselisib (GDC-0032) in PIK3CA -mutated locally advanced or metastatic solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr CT046.