A Study of MORAb-202 Versus Investigator's Choice Chemotherapy in Female Participants With Platinum-resistant High-grade Serous (HGS) Ovarian, Primary Peritoneal, or Fallopian Tube Cancer

Inclusion Criteria: * Female participants with histologically-confirmed diagnosis of HGS ovarian, primary peritoneal, or fallopian tube cancer. * Platinum-resistant disease, defined as: * For participants who had only 1 line of platinum-based therapy: progression between \> 1 month and ≤ 6 months after the last dose of platinum-based therapy of at least 4 cycles. * For participants who had 2 or 3 lines of platinum-based therapy: progression ≤ 6 months after the last dose of platinum-based therapy. * Participants have received at least 1 but no more than 3 prior lines of systemic therapy and for whom single-agent therapy is appropriate as the next line of therapy. Participants may have been treated with up to 1 line of therapy subsequent to determination of platinum-resistance. * Disease progression per RECIST v1.1 (by investigator assessment) of at least 1 measurable lesion on or after the most recent therapy. * Either formalin-fixed, paraffin-embedded (FFPE) tissue (up to 5 years old) or newly-obtained biopsies must be available for FRα assessment prior to randomization. * Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0 or 1. Exclusion Criteria: Medical Conditions * Clear cell, mucinous, endometrioid or sarcomatous histology, or mixed tumors containing components of any of these histologies, or low grade or borderline ovarian cancer. * Primary platinum-refractory ovarian cancer defined as disease progression within 1 month of the last dose of the fir…