First in Human Study of IMGN151 in Recurrent Endometrial Cancer and Recurrent, High-grade Serous Epithelial Ovarian, Primary Peritoneal, or Fallopian Tube Cancers

Open to females ages 18 years and up

1. Patients ≥ 18 years of age
2. Patients must have an Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0 or 1.
3. Dose-Escalation Phase: Patients must have a confirmed diagnosis of recurrent endometrial cancer or high-grade serous epithelial ovarian cancer (EOC), primary peritoneal, or fallopian tube cancer.

4. Expansion Phase: Patients must have a confirmed diagnosis of recurrent endometrial cancer or platinum-resistant, high-grade serous epithelial ovarian cancer (PROC), primary peritoneal, or fallopian tube cancer.

   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.

5. Prior anticancer therapy
   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.
6. Evaluable lesions
   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).
7. Patients must be willing to provide an archival tumor tissue block or slides or to undergo a procedure to obtain a new biopsy using a low-risk, medically routine procedure for retrospective IHC confirmation of FRα status.
8. Patients must have completed prior therapy within the specified times below:
   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
9. Patients must have stabilized or recovered (Grade 1 or baseline) from all prior therapy-related toxicities (except alopecia).
10. Patients must have completed any major surgery at least 4 weeks before the first dose of IMGN151 and have recovered or stabilized from the side effects of prior surgery before the first dose of IMGN151.
11. Patients must have adequate hematologic, liver, and kidney functions defined as follows:
    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
12. Patients must be willing and able to sign the informed consent form (ICF) and to adhere to the protocol requirements.
13. Females of childbearing potential (FOCBP) must agree to use highly effective contraceptive method(s) while on IMGN151 and for at least 3 months after the last dose.
14. FOCBP must have a negative serum pregnancy test at Screening and a negative serum or urine pregnancy test within 72 hours before the first dose of IMGN151.

1. Patients with endometrioid, clear cell, mucinous, or sarcomatous histology, mixed tumors containing any of the above histologies, or low-grade/borderline ovarian tumor
2. Patients with prior wide-field radiotherapy affecting at least 20% of the bone marrow
3. Patients with > Grade 1 peripheral neuropathy per CTCAE v5.0
4. Patients 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
5. Patients 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. 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.
6. Patients with a history of multiple sclerosis or other demyelinating disease and/or Lambert-Eaton syndrome (paraneoplastic syndrome)
7. Patients with clinically significant cardiac disease including, but not limited to, any of the following:
   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
8. Patients with a history of hemorrhagic or ischemic stroke within 6 months before enrollment
9. Patients with a history of cirrhotic liver disease (Child-Pugh Class B or C)
10. Patients with evidence of pneumonitis on baseline imaging or patients with a previous clinical diagnosis of noninfectious interstitial lung disease (ILD), including noninfectious pneumonitis
11. Patients requiring use of folate-containing supplements (eg, folate deficiency)
12. Patients with prior hypersensitivity to monoclonal antibodies (mAb)
13. Females who are pregnant or breastfeeding
14. For Expansion Phase: Patients who received a prior FRα-targeting agent
15. Patients with untreated or symptomatic central nervous system metastases
16. Patients with a history of other malignancy within 3 years before enrollment Note: Patients 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.
17. Prior known hypersensitivity reactions to study drugs and/or any of their excipients