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, primaryperitoneal, 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 4cycles.

• For participants who had 2 or 3 lines of platinum-based therapy: progression ≤ 6months after the last dose of platinum-based therapy.

• Participants have received at least 1 but no more than 3 prior lines of systemictherapy and for whom single-agent therapy is appropriate as the next line oftherapy. Participants may have been treated with up to 1 line of therapy subsequentto determination of platinum-resistance.

• Disease progression per RECIST v1.1 (by investigator assessment) of at least 1measurable lesion on or after the most recent therapy.

• Either formalin-fixed, paraffin-embedded (FFPE) tissue (up to 5 years old) ornewly-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 tumorscontaining components of any of these histologies, or low grade or borderlineovarian cancer.

• Primary platinum-refractory ovarian cancer defined as disease progression within 1month of the last dose of the first line platinum-containing regimen.

• Pulmonary function test (PFT) abnormalities: FEV1 < 70% or FVC < 60%, and DLCO < 80%.

• Investigator-assessed current ILD/pneumonitis, or ILD/pneumonitis suspected atscreening or history of ILD/pneumonitis of any severity including ILD/pneumonitisfrom prior anti-cancer therapy.

• Significant third-space fluid retention (eg, ascites or pleural effusion) thatrequires repeated drainage.

Physical and Laboratory Test Findings

• Evidence of organ dysfunction or any clinically-significant deviation from normal inphysical examination, vital signs, ECG, or clinical laboratory determinations beyondwhat is consistent with the target population.

Allergies and Adverse Drug Reactions

• Has any prior severe hypersensitivity (≥ Grade 3) to monoclonal antibodies oreribulin or contraindication to the receipt of corticosteroids or any of theexcipients (investigators should refer to the prescribing information for theselected corticosteroid).

• History of allergy or contraindication to IC chemotherapy agent selected ifrandomized to Arm C.

Other protocol-defined inclusion/exclusion criteria apply.