A Phase 1, First-in-Human, Open-Label, Dose-Escalation and Expansion Study of IMGN151 (anti-FRa antibody-drug conjugate) in Adult Patients with Recurrent Endometrial Cancer and Recurrent, High-Grade Recurrent Endometrial Cancer and Recurrent, High-Grade Serous Epithelial Ovarian, Primary Peritoneal, or Fallopian Tube Cancers

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.

1. For Expansion Phase: Patients must have recurrent endometrial cancer or patients with PROC must have received 1-4 prior systemic lines of therapy.
2. Neoadjuvant ± adjuvant therapies are considered 1 line of therapy.
3. Maintenance therapy (eg, bevacizumab or poly [ADP-ribose] polymerase [PARP] inhibitors) will be considered part of the preceding line of therapy (ie, not counted independently).
4. Therapy changed due to toxicity in the absence of progression will be considered part of the same line (ie, not counted independently).
5. Hormonal therapy will be counted as a separate line of therapy unless it was given as maintenance.

1. Dose-Escalation Phase: Patients may have radiologically evaluable or nonevaluable disease.
2. Expansion Phase: Patients must have at least 1 lesion that meets the definition of measurable disease by RECIST v1.1 (radiologically measured by the investigator).

1. Systemic antineoplastic therapy within 5 half-lives or 4 weeks (whichever is shorter) before the first dose of IMGN151
2. Focal radiation completed at least 2 weeks before the first dose of IMGN151

1. Absolute neutrophil count (ANC) ≥ 1.5 ×10 9/L (1500/μL) without granulocyte colony-stimulating factor (G-CSF) in the prior 10 days or long-acting white blood cell growth factors in the prior 20 days
2. Platelet count ≥ 100 × 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 transfusion in the prior 21 days
4. Estimated glomerular filtration rate (eGFR) ≥ 60 mL/min/1.73 m2 or an estimated creatinine clearance of ≥ 60 mL/min
5. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 3.0 × upper limit of normal (ULN)
6. Serum bilirubin ≤ 1.5 × ULN (patients with documented diagnosis of Gilbert syndrome are eligible if total bilirubin < 3.0 × ULN)
7. Serum albumin ≥ 2 g/dL

1. Active hepatitis B or C infection (whether or not on active antiviral therapy)
2. HIV infection in patients with CD4+ T-cell (CD4+) counts < 350 cells/µL
3. Active cytomegalovirus infection
4. Active COVID-19/SARS-CoV-2 infection. Although SARS-CoV-2 testing is not mandatory for study entry, testing should follow local clinical practice guidelines and standards
5. Any other concurrent infectious disease requiring IV antibiotics within 2 weeks before the first dose of IMGN151 Note: Testing at Screening is not required for the above infections unless clinically indicated.

1. Myocardial infarction ≤ 6 months before the first dose
2. Unstable angina pectoris
3. Uncontrolled congestive heart failure (New York Heart Association > class II)
4. Uncontrolled ≥ Grade 3 hypertension (per CTCAE v5.0)
5. Uncontrolled cardiac arrhythmias
6. QTc interval > 470 ms