Identification of predictive markers of clinical activity from a phase II trial of single agent pertuzumab (rhuMab 2C4), a HER dimerization inhibitor, in advanced ovarian cancer (OC)

Abstract

3001 Background: Pertuzumab (P), a humanized HER2 antibody, represents a new class of targeted agents called HER dimerization inhibitors (HDIs). P inhibits dimerization of HER2 with EGFR, HER3 and HER4, and subsequently inhibits signaling through MAP and PI3 kinases. Interim data from a phase II trial suggested that P has activity in OC, especially in a subset of tumors with activated HER2 (Abstract #5051 ASCO 2005). Methods: 123 pts with relapsed OC were treated with P. Cohort 1 was treated with 840mg followed by 420mg and cohort 2 with 1050mg every 3 weeks. Fresh tissue biopsies were mandated from Cohort 1, and archival formalin fixed paraffin tissue (FFPET ) were obtained from both cohorts. Molecular expression studies from FFPET and fresh tissue were conducted. Results: From final data of 117 evaluable pts, 5 pts had objective partial responses (RR = 4.3%). Eight pts (6.8%) had SD for ≥ 6 months, and an additional 4 pts (3.4%) had SD with CA-125 reduction of ≥50%. Overall rate of activity = 14.5%. Of the 65 fresh tumor biopsies, 28 were evaluable and 8 (28.6%) were positive for phosphorylated HER2 (pHER2) by ELISA. Among pts who had pHER2 status determined, TTP was 20.9 weeks for pHER2+ pts (n=8), compared to 5.8 weeks for pHER2- (n = 20). Data from microarray expression profiling were analyzed with respect to pHER2 status from the same tumors. The expression levels of HER2, EGFR and HER3 in combination with the expression of certain HER ligands may be predictive of pHER2 status. We have extended these analyses to qRT-PCR from macrodissected FFPET of HER receptors and ligands. This was analyzed with respect to clinical outcome. Preliminary analyses of expression data suggest that HER receptors and ligands may be promising candidates for diagnostic markers. Updated data in 78 OC pts will be presented. Conclusions: Clinical activity was observed in 14.5% of pts with heavily pretreated OC (PRs, SD ≥ 6 months, and SD with CA-125 reductions of ≥50%). This study suggests that P may be active in OC, and that specific HER receptors and ligands may be promising diagnostics for identifying tumors responsive to P. [Table: see text]