This study is designed to evaluate the efficacy and safety of mirvetuximab soravtansine (MIRV) in participants with platinum-resistant high-grade serous epithelial ovarian cancer, primary peritoneal, or fallopian tube cancer, whose tumors express a high-level of Folate Receptor-Alpha (FRα). Participants will be, in the opinion of the Investigator, appropriate for single-agent therapy for their next line of therapy. All participants will receive single-agent MIRV at 6 mg/kg adjusted ideal body weight administered on Day 1 of every 3-week cycle.

This study is designed to evaluate the efficacy and safety of mirvetuximab soravtansine (MIRV) in participants with platinum-resistant high-grade serous epithelial ovarian cancer, primary peritoneal, or fallopian tube cancer, whose tumors express a high-level of Folate Receptor Alpha (FRα). Participants will be, in the opinion of the Investigator, appropriate for single-agent therapy for their next line of therapy. FRα positivity will be defined by the Ventana FOLR1 (Folate Receptor 1/Folate Receptor Alpha) Assay.

Approximately 110 eligible participants will be enrolled to achieve a total of 105 efficacy evaluable participants. Efficacy evaluable participants include those who have measurable lesions per Response Evaluation Criteria in Solid Tumors, version 1.1 (RECIST v1.1) at baseline and received at least 1 dose of MIRV.

All participants will receive single-agent MIRV at 6 mg/kg adjusted ideal body weight (AIBW) administered on Day 1 of every 3-week cycle (Q3W).

Tumor response will be evaluated by the Investigator using RECIST v1.1. Computerized tomography (CT) or magnetic resonance imaging (MRI) scans will be collected for sensitivity analysis by blinded independent central review (BICR).

Participants will continue to receive MIRV until disease progression, unacceptable toxicity, withdrawal of consent, death, or until the Sponsor terminates the study (whichever comes first).

Tumor assessments, including radiological assessments by CT/MRI scans will be performed at Screening and subsequently every 6 weeks (± 1 week) from Cycle 1 Day 1 (C1D1) for the first 36 weeks then every 12 weeks (± 3 weeks) until disease progression, death, the start of new anticancer therapy, or participant's withdrawal of consent (whichever occurs first).

Participants who discontinue MIRV for reasons other than progressive disease (PD) will continue with tumor assessments until documentation of PD or the start of a new anticancer therapy, whichever comes first. Prior to Week 36 (from Cycle 1, Day 1), assessments should occur every 6 weeks (± 1 week) as allowed by local requirements but must occur at an interval of no more than 12 weeks. After Week 36, assessment will occur every 12 weeks (± 3 weeks) until documentation of PD or the start of new anticancer therapy.

All participants who discontinue MIRV will be followed for survival every 3 months (± 1 month) until death, lost to follow-up, withdrawal of consent for survival follow-up, or end of study (EOS) (whichever comes first). Additional survival follow-up calls may occur periodically, if needed.

Inclusion Criteria:

1. Female participants ≥ 18 years of age

2. Participants must have a confirmed diagnosis of high-grade serous epithelial ovarian cancer (EOC), primary peritoneal cancer, or fallopian tube cancer

3. Participants must have platinum-resistant disease:

   1. Participants who have only had 1 line of platinum based therapy must have received at least 4 cycles of platinum, must have had a response (complete response/remission [CR] or partial response/remission [PR]) and then progressed between > 3 months and ≤ 6 months after the date of the last dose of platinum
   2. Participants who have received 2 or 3 lines of platinum therapy must have progressed on or within 6 months after the date of the last dose of platinum

   Note: Progression should be calculated from the date of the last administered dose of platinum therapy to the date of the radiographic imaging showing progression

   Note: Participants who are platinum refractory during front-line treatment are excluded (see exclusion criteria)

4. Participants must have progressed radiographically on or after their most recent line of anticancer therapy.

5. Participants must be willing to provide an archival tumor tissue block or slides, or undergo procedure to obtain a new biopsy using a low-risk, medically routine procedure for immunohistochemistry (IHC) confirmation of Folate Receptor α (FRα) positivity

6. Participant's tumor must be positive for FRα expression as defined by the Ventana FOLR1 Assay

7. Participants must have at least 1 lesion that meets the definition of measurable disease by RECIST v1.1 (radiologically measured by the Investigator)

8. Participants must have received at least 1 but no more than 3 prior systemic lines of anticancer therapy, including at least 1 line of therapy containing bevacizumab, and for whom single-agent therapy is appropriate as the next line of treatment:

   1. Adjuvant ± neoadjuvant considered 1 line of therapy
   2. Maintenance therapy (e.g., bevacizumab, poly adenosine diphosphate-ribose polymerase (PARP) inhibitors) will be considered part of the preceding line of therapy (i.e., not counted independently)
   3. Therapy changed due to toxicity in the absence of progression will be considered part of the same line (i.e., not counted independently)
   4. Hormonal therapy will be counted as a separate line of therapy unless it was given as maintenance

9. Participants must have an Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0 or 1

10. Participants must have completed prior therapy within the specified times below:

    1. Systemic antineoplastic therapy within 5 half-lives or 4 weeks (whichever is shorter) prior to first dose of MIRV
    2. Focal radiation completed at least 2 weeks prior to first dose of MIRV

11. Participants must have stabilized or recovered (Grade 1 or baseline) from all prior therapy-related toxicities (except alopecia)

12. Participants must have completed any major surgery at least 4 weeks prior to first dose of MIRV and have recovered or stabilized from the side effects of prior surgery

13. Participants must have adequate hematologic, liver and kidney functions defined as:

    1. Absolute neutrophil count (ANC) ≥ 1.5 x 10^9/L (1,500/μL) without G-CSF in the prior 10 days or long-acting WBC growth factors in the prior 20 days
    2. Platelet count ≥ 100 x 10^9/L (100,000/μL) without platelet transfusion in the prior 10 days
    3. Hemoglobin ≥ 9.0 g/dL without packed red blood cell (PRBC) transfusion in the prior 21 days
    4. Serum creatinine ≤ 1.5 x upper limit of normal (ULN)
    5. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 3.0 x ULN
    6. Serum bilirubin ≤ 1.5 x ULN (patients with documented diagnosis of Gilbert syndrome are eligible if total bilirubin < 3.0 x ULN)
    7. Serum albumin ≥ 2 g/dL

14. Participants or their legally authorized representative must be willing and able to sign the informed consent form (ICF) and to adhere to the protocol requirements

15. Women of childbearing potential (WCBP) must agree to use highly effective contraceptive method(s) while on MIRV and for at least 3 months after the last dose

16. WCBP must have a negative pregnancy test within the 4 days prior to the first dose of MIRV

Exclusion Criteria:

1. Male participants

2. Participants with endometrioid, clear cell, mucinous, or sarcomatous histology, mixed tumors containing any of the above histologies, or low-grade/borderline ovarian tumor

3. Participants with primary platinum-refractory disease, defined as disease that did not respond to (CR or PR) or has progressed within 3 months of the last dose of first-line platinum-containing chemotherapy

4. Participants with prior wide-field radiotherapy (RT) affecting at least 20 percent of the bone marrow

5. Participants with > Grade 1 peripheral neuropathy per Common Terminology Criteria for Adverse Events (CTCAE)

6. Participants with active or chronic corneal disorders, history of corneal transplantation, or active ocular conditions requiring ongoing treatment/monitoring, such as uncontrolled glaucoma, wet age-related macular degeneration requiring intravitreal injections, active diabetic retinopathy with macular edema, macular degeneration, presence of papilledema, and /or monocular vision

7. Participants with serious concurrent illness or clinically relevant active infection, including, but not limited to the following:

   1. Active hepatitis B or C infection (whether or not on active antiviral therapy)
   2. Human immunodeficiency virus (HIV) infection
   3. Active cytomegalovirus infection
   4. Any other concurrent infectious disease requiring IV antibiotics within 2 weeks prior to the first dose of MIRV

   Note: Testing at screening is not required for the above infections unless clinically indicated

8. Participants with a history of multiple sclerosis (MS) or other demyelinating disease and/or Lambert-Eaton syndrome (paraneoplastic syndrome)

9. Participants with clinically significant cardiac disease including, but not limited to, any of the following:

   1. Myocardial infarction ≤ 6 months prior to first dose
   2. Unstable angina pectoris
   3. Uncontrolled congestive heart failure (New York Heart Association > class II)
   4. Uncontrolled ≥ Grade 3 hypertension (per CTCAE)
   5. Uncontrolled cardiac arrhythmias

10. Participants with a history of hemorrhagic or ischemic stroke within 6 months prior to enrollment

11. Participants with a history of cirrhotic liver disease (Child-Pugh Class B or C)

12. Participants with a previous clinical diagnosis of noninfectious interstitial lung disease (ILD), including noninfectious pneumonitis

13. Participants requiring use of folate-containing supplements (eg, folate deficiency)

14. Participants with prior hypersensitivity to monoclonal antibodies (mAb)

15. Women who are pregnant or breastfeeding

16. Participants who received prior treatment with MIRV or other FRα-targeting agents

17. Participants with untreated or symptomatic central nervous system (CNS) metastases

18. Participants with a history of other malignancy within 3 years prior to enrollment.

    Note: Participants with tumors with a negligible risk for metastasis or death (eg, adequately controlled basal-cell carcinoma or squamous-cell carcinoma of the skin, or carcinoma in situ of the cervix or breast) are eligible

19. Prior known hypersensitivity reactions to study drugs and/or any of their excipients