Merck & Co. Inc. / Endocyte, Inc.

Platinum-Resistant Ovarian Cancer

Disease Overview

Platinum-resistant ovarian cancer is defined as disease that progresses within six months of platinum-based chemotherapy. It carries a particularly poor prognosis with limited effective treatment options and short progression-free survival. Folate receptor overexpression in many ovarian tumors creates a targeted therapy opportunity with companion diagnostic-based patient selection.

Competitive Landscape

When Merck and Endocyte signed their April 2012 worldwide collaboration on vintafolide (EC145), the platinum-resistant ovarian cancer (PROC) landscape relied on single-agent pegylated liposomal doxorubicin (Doxil), topotecan, weekly paclitaxel, and gemcitabine — none of which produced durable responses. Vintafolide was a folate-vinca alkaloid conjugate paired with the etarfolatide (EC20) imaging companion diagnostic for folate-receptor patient selection, with a Phase 2 PRECEDENT signal of 5.0 vs 2.7 month PFS supporting Phase 3 entry. The deal was structured as $120M upfront plus $880M in milestones across six potential cancer indications, plus 50/50 US profit share and double-digit ex-US royalty. The Phase 3 PROCEED trial was halted for futility in May 2014 after DSMB interim analysis showed no PFS benefit; Endocyte stock fell 62% on the announcement and Merck terminated the collaboration shortly thereafter. The PROC space has since been transformed by mirvetuximab soravtansine (Elahere, ImmunoGen/AbbVie, FRα ADC, FDA approved 2022) — vindicating the folate-receptor target hypothesis but with an ADC modality rather than the folate-conjugate approach Endocyte and Merck pursued. PARP inhibitors (Lynparza, Zejula, Rubraca) and bevacizumab also reshaped the broader ovarian treatment paradigm.