Study to Assess Adverse Events and Change in Disease Activity in Adult Participants With Advanced Solid Tumors Receiving Intravenous (IV) ABBV-400

Inclusion Criteria:

Histologic malignant solid tumor diagnosis (World Health Organization [WHO] criteria).
Measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1.
For Part 1 only - history of advanced solid tumor that has progressed on all standard of care therapy and are not amenable to surgical resection or other approved therapeutic options that have demonstrated clinical benefit.

For Part 2 only -history of advanced c-Met overexpressing non-squamous wtEGFR or mutEGFR or history of advanced c-Met overexpressing squamous Non-Small Cell Lung Cancer (NSCLC) that have progressed after treatment per the protocol.

Should have no more than 2 lines of prior cytotoxic chemotherapy excluding adjuvant therapy and must have advanced NSCLC that is not amenable to surgical resection or other approved therapeutic options that have demonstrated clinical benefit.
For Part 3 only - history of advanced histopathologically or cytologically confirmed diagnosis of c-Met overexpressing GEA that has progressed after treatment with at least 1 prior cytotoxic chemotherapeutic regimen for locally advanced or metastatic disease and have not received more than 2 prior lines of cytotoxic chemotherapy regimens. If applicable, participants must have progressed on an immune checkpoint inhibitor or appropriate available therapies.
Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0 or 1.
Laboratory values meeting the criteria outlined in the protocol.

Exclusion Criteria:

History of interstitial lung disease (ILD) or pneumonitis that required treatment with systemic steroids, nor any evidence of active ILD or pneumonitis.
History of idiopathic pulmonary fibrosis, organizing pneumonia (e.g., bronchiolitis obliterans), drug-induced pneumonitis, or idiopathic pneumonitis.