A Study of XMT-2056 in Advanced/Recurrent Solid Tumors That Express HER2

Inclusion Criteria

• •Participant has recurrent or metastatic solid tumors with HER2 expression and has disease progression after treatment, is intolerant to treatment, or is contraindicated with available anti-cancer therapies known to confer benefit, based on investigator's judgement. Note: Participants must have HER2 positivity per the results of their most recent tumor tissue testing, defined as IHC 3+ or IHC 2+ in combination with in situ hybridization (ISH)+. Participants with ERBB2-activating mutations or ERBB2 gene amplification in the absence of HER2 positivity are considered ineligible.
• •Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1.
• •Participant must have measurable disease as defined by RECIST version 1.1.
• •Participant has fresh tumor biopsy tissue available for submission to central laboratory. If obtaining fresh tumor tissue is medically contraindicated, archival tumor tissue can be submitted following written approval of the request by the study Medical Monitor. Samples must be obtained after the participant's most recent HER2-targeting therapy unless determined to be medically contraindicated after discussion with the medical monitor.
• •2. In addition, participants must be either off corticosteroids, or on a stable/decreasing dose of ≤ 10 mg prednisone daily (or equivalent).