Inclusion Criteria:

* ≥18 years of age
* Eastern Cooperative Oncology Group performance status (ECOG PS) of 0, 1 or 2
* Histological or cytological diagnosis of a solid tumor
* Participants must be refractory to or have relapsed after at least one prior standard therapeutic regimen. Participants must be relapsed or refractory to, have developed an intolerance to, or not be candidates for available therapies with established benefit.
* Participants must have measurable disease as per RECIST v.1.1 based on imaging performed during Screening.
* During screening, participants must have positive FAP PET/CT uptake as described in criteria for continuation of IM-3050 treatment.
* Participants must have adequate organ function.

Exclusion Criteria:

* Participant has received certain prior radiation therapy as detailed in the protocol
* Participant has undergone major surgery within 4 weeks or minor surgery within 2 weeks of starting 177Lu-IM-3050 or has known active central nervous system (CNS) primary tumor or metastases and/or carcinomatous meningitis.
* Participant has a known history of malignant primary brain tumor, or another primary solid or hematologic malignancy (other than that under study), unless the participant has undergone potentially curative therapy with no evidence of that disease for at least 3 years.

Exception: The time requirement does not apply to participants who underwent successful definitive resection of certain cancers.

* Recent or ongoing serious infection or other significant medical condition as detailed in the protocol.
* Participant has received an investigational product or been treated with an investigational device within 30 days, or 5 half-lives prior to receiving the FAP PET/CT imaging tracer or 177Lu-IM-3050.