Exploratory phase II evaluation of cabozantinib in recurrent/metastatic uterine carcinosarcoma (CS): A study of the Princess Margaret, Chicago, and California phase II consortia.

5587 Background: Carcinosarcoma (CS) is a rare ( < 5%) aggressive subtype of endometrial cancer (EC). Patients (pts) with progression on platinum-based chemotherapy (CTX) have limited options, there is no standard 2ndline treatment and median progression-free survival (PFS) is < 2months (mt), 6-mt PFS less than 20%. Limited molecular data on CS aligns with epithelial EC, providing rationale for evaluating similar strategies such as targeting MET and angiogenesis. Cabozantinib (cabo) is multi-targeted tyrosine kinase inhibitor against MET, VEGFR, TIE2, RET, AXL and KIT. Methods: PHL-86 (NCI#9322/NCT01935934) is a multi-centre, non-randomized, phase II trial of cabo (60 mg oral daily dose on a 28-day cycle) in EC pts recurring within a year of adjuvant CTX or with progression after 1stline of CTX for metastatic disease. Pts with rare histology including CS, were enrolled in an exploratory cohort. Activity of interest for further evaluation was defined as 4 responses (either partial response [PR] or 12-wk PFS) out of 10 pts of a given histotype. CT scans were performed after cycle 3 and every 2 cycles thereafter. Results: From 2013 to 2016, 32 pts were treated in the exploratory cohort, 19 pts with CS. Median age was 66 years (range 25-75); prior treatment included CTX (17: 1 line, 6: 2 lines) and/or radiation (11). Fifteen pts were evaluable for response, with 1 PR (7%) and 8 pts with 12-wk PFS (53%). Median PFS was 3 mt (95% CI: 2.7 – 4.6) with estimated 6-mt PFS of 13% (2 to 33%). Toxicity evaluation is available for 19 pts. Common events were fatigue and GI upset. Most frequent > Grade3 toxicities were hypertension (5), anemia (4), diarrhea (2). Four pts had GI fistula (2) or perforation (2). Mutation profiling in archival tissue showed TP53 (73%), PIK3CA (40%), KRAS (27%), PTEN(13%) with > 1 mutation present in 14/15 pts analyzed. The 1 pt with no somatic mutations had a PR (31% decrease) on cabo (PFS 6.7mt). Conclusions: Cabo in CS cohort met the predefined endpoint for further evaluation and compares favourably with other agents in this poor prognosis disease. Larger studies are required to define depth and durability of response and identify relevant biomarkers. Clinical trial information: NCT01935934.

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