Phase II study of cabozantinib (cabo) in patients (pts) with recurrent/metastatic endometrial cancer (EC): A study of the Princess Margaret, Chicago, and California phase II consortia.

5524 Background: Recurrent/metastatic EC has a poor prognosis with no standard 2 nd line therapy. Cabo is a multi-targeted kinase inhibitor of MET, VEGFR, TIE2, AXL & KIT, relevant in epithelial-stromal cross-talk. The role of MET/HGF in aggressive EC biology, where transient benefit of VEGF-targeting is due to MET/HGF, TIE2 & AXL, provides rationale for MET targeting in EC. Methods: PHL86 (NCI#9322/NCT01935934) is a multi-centre, phase II trial of cabo (60mg oral daily dose) in pts with EC recurring within a year of adjuvant chemotherapy (ctx), or with progression after 1 line of ctx for metastatic disease. Experimental (E) cohort was stratified by histology (serous (SER) vs endometroid (END)) in a Simon two-stage design for co-primary endpoints of response rate ( > 30%) & 12-week progression-free-survival (PFS) ( > 55%). Activity was defined as > 7 partial responses (PRs) or > 15 instances of 12 wk-PFS in 36 pts. Pts with rare histology EC were treated in a parallel exploratory (Ex) cohort. Results: From May 2013 to Nov 2016, 102 pts (E: 71; Ex: 31) have been treated with cabo after prior radiation (59) and/or ctx (no. lines: 1(77); 2(22)). Cabo was well tolerated with common toxicities of fatigue, nausea, diarrhea & hand-foot syndrome. Most frequent Grade 3/4 toxicity was hypertension (32/101 pts). Fistula/perforation occurred in 4 of 71 SER/END pts & 4 of 31 Ex pts; no risk factors were identified. In 33 END pts, 6 PRs & 24 instances of > 12-wk PFS were observed; median PFS is 4.8 mths (95% CI: 4.4 – 6.4) with estimated 6-mth PFS of 43% (95% CI: 27 to 59%). In 34 SER pts, 4 PRs & 20 instances of > 12-wk PFS were observed; median PFS is 4.0 mths (95% CI: 2.7 – 4.7) with estimated 6-mth PFS of 30% (95% CI: 15 to 46%). 4 pts have had PFS > 12 mths, 1 SER pt remains on study after 25mths. Mutational analysis demonstrated presence of KRAS with PTEN or PIK3CA mutations in 9 (SER/END) pts, of whom 8/9 pts met 12-wk PFS endpoint, with a median PFS 5.9 mth (4.1 to 15.4). Conclusions: Cabo has single agent activity in END and SER EC with durable disease control. Concurrent mutation in KRAS/PTEN/PIK3CA may enrich for response. The current data support further evaluation of cabo in EC. Clinical trial information: NCT01935934.