Phase 2 study of the pan-isoform PI3 kinase inhibitor BKM120 in metastatic urothelial carcinoma patients.

Abstract

324 Background: PI3 kinase (PI3K) pathway alterations are found in 39% of urothelial carcinoma (UC) (TCGA). Prior reports have shown significant responses in metastatic UC patients (pts) whose tumors harbor PI3K pathway alterations treated with mTOR inhibitors, providing a rationale to investigate BKM120 in mUC. Methods: This phase II study enrolled mUC pts progressing on platinum-based chemotherapy (up to 4 prior agents). The primary and secondary endpoints were proportion of pts progression-free at 2 months and response rate (RR) by Response Criteria in Solid Tumors (RECIST) v1.1, respectively. A Simon 2-stage design was used to discriminate between a 2 month PFS rate of <60% (at which point the trial would be halted) vs. >80%. Pts received 100 mg drug once daily. To identify predictors of response/resistance to BKM120, targeted exon capture sequencing was performed to define the mutation status of PIK3CA, PTEN, AKT1, TSC1, and additional genes within tumors from all treated pts. Results: 13 of 15 enrolled pts were eligible for the primary endpoint. Median age was 65 (53-82). Pts had received an average of 3 agents (2-4) before enrollment. The median progression-free survival (PFS) was 2.77 months (95% CI: 1.83-3.71) with 6 pts displaying stable disease (SD) and 1 partial response (PR) at 2 months (PFS rate 54%). Sequencing identified 2 pts with PIK3CA mutations (E542K, H1047R) who experienced progression as best RECIST response. Tumor from the pt with a 16 month PR harbored a TSC1 R500* nonsense mutation. 1 pt with SD lasting 3.7 months had a TSC1 L330fs truncation. Conclusions: While BKM120 therapy did not display a significant improvement in 2-month PFS rate compared to standard chemotherapy in the second-line setting, 2 pts, one with a durable PR and one with SD, had tumors with inactivating mutations in TSC1. Based upon these results, an expansion cohort is accruing in which select mUC pts whose tumors harbor PI3K pathway alterations receive BKM120. Clinical trial information: NCT01551030.