A Study of XMT-1660 in Participants With Solid Tumors

Open to people ages 18 years and up

• Recurrent or advanced solid tumor and has disease progression after treatment with available anti-cancer therapies known to confer benefit or is intolerant to treatment.
• Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1
• At least one measurable lesion(s) as defined by RECIST version 1.1.
• Tumor tissue, either archival or from a fresh tumor biopsy, available for testing or be willing to undergo a minimally invasive tumor biopsy to obtain tumor tissue for local testing, if not medically contraindicated, prior to Cycle 1 Day 1
• Brain magnetic resonance imaging (MRI) during the Pre- Screening/Screening period unless obtained within 30 days prior to enrollment (based on standard clinical care), if they meet either of the following criteria:
  1. All participants with TNBC
  2. Participants with a history of brain metastases or with neurologic symptoms or signs suspicious for brain metastases.

• Prior treatment with an Antibody Drug Conjugate (ADC) containing an auristatin payload. Prior treatment with another ADC containing other payloads is allowed.
• Major surgery within 28 days of starting study treatment, systemic anticancer therapy within the time period of 28 days or 5 half-lives of the prior therapy before starting study treatment (14 days or 5 half-lives for small molecule targeted therapy), whichever is less, or palliative radiation therapy within 14 days of starting study treatment.
• Diagnosis of additional malignancy that required active treatment (including surgery, systemic therapy, and radiation) within 2 years prior to screening, except for adequately treated basal cell or squamous cell skin cancer, or carcinoma in situ of the breast or of the cervix.
• Untreated CNS metastases (including new and progressive brain metastases), history of leptomeningeal metastasis or carcinomatous meningitis.
  1. Participants are eligible if CNS metastases are adequately treated, and participants are neurologically stable for at least 2 weeks prior to enrollment.
  2. In addition, participants must be either off corticosteroids, or on a stable/decreasing dose of ≤ 10 mg daily prednisone (or equivalent). Anticonvulsants are allowed except for those drugs associated with liver toxicity
  3. Participants may be eligible if CNS lesions are asymptomatic, equivocal for metastases or do not require specific therapy in the opinion of the investigator
• Prior B7-H4 targeted treatment.
• History of cirrhosis, hepatic fibrosis, esophageal or gastric varices, or other clinically significant liver diseases.
• Current severe, uncontrolled systemic disease (e.g. clinically significant cardiovascular, pulmonary, or metabolic disease) or intercurrent illness that could increase the risk of serious adverse events (SAEs) or interfere with per-protocol evaluations, in the judgment of either the Sponsor or the Investigator.
• Clinically significant cardiovascular disease