A Study of XMT-1660 in Participants With Solid Tumors

Inclusion Criteria:

Participant has proven 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
Participant must have at least one measurable lesion(s) as defined by RECIST version 1.1.
Participant must be willing to undergo a minimally invasive tumor biopsy to obtain tumor tissue for local testing, if medically feasible, prior to C1D1. If the investigator feels a biopsy is not medically feasible, an exemption request must be submitted to the study Medical Monitor for approval.

Exclusion Criteria:

Prior treatment with an Antibody Drug Conjugate (ADC) containing an auristatin or maytansinoid 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.
Participant has current severe, uncontrolled systemic disease (e.g., clinically significant cardiovascular, pulmonary, or metabolic disease) or intercurrent illness that could interfere with per-protocol evaluations. Further, participants are excluded with the following characteristics:

Participant has untreated CNS metastases (including new and progressive brain metastases), history of leptomeningeal metastasis or carcinomatous meningitis.

Participants are eligible if CNS metastases are adequately treated, and participants are neurologically stable for at least 2 weeks prior to enrollment.
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