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

Inclusion Criteria:

• Laboratory values meeting the criteria laid out in the protocol.

• Measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1.

• Documented diagnosis of locally advanced or metastatic hepatocellular carcinoma (HCC), pancreatic ductal adenocarcinoma (PDAC), biliary tract cancers (BTC),squamous cell carcinoma of the esophagus, (ESCC), triple negative breast cancer (TNBC), hormone receptor+/HER2-breast cancer (HR+/HER2-BC), head and necksquamous-cell-carcinoma (HNSCC), or Platinum Resistant High Grade Epithelial OvarianCancer (PROC)/primary peritoneal/fallopian tube cancer (by World Health Organization [WHO] criteria). Participant meets the criteria for disease activity laid out in theprotocol.

Exclusion Criteria:

• Have received anticancer therapy including chemotherapy, radiation therapy,immunotherapy, biologic, or any investigational therapy within 28 days or 5half-lives of the drug (whichever is shorter) prior to the first dose of ABBV-400.Palliative radiation therapy for bone, skin, or subcutaneous metastases with 10fractions or less is permitted and not subject to a washout period.

• Unresolved clinically significant AEs > Grade 1 from prior anticancer therapy.

• History of interstitial lung disease (ILD) or pneumonitis that required treatmentwith systemic steroids, or any evidence of active ILD or pneumonitis, including butnot limited to those listed in the protocol.

• History of clinically significant, intercurrent lung-specific illnesses, includingthose laid out in the protocol.

• Untreated brain or meningeal metastases (i.e., participants with history ofmetastases are eligible provided they do not require ongoing steroid treatment forcerebral edema and have shown clinical and radiographic stability for at least 14days after definitive therapy). Participants may continue on antiepileptic therapyif required.

• History of other active malignancy, with the exception of those laid out in theprotocol.

• Any autoimmune, connective tissue or inflammatory disorders with documented orsuspicious pulmonary involvement at screening (i.e., rheumatoid arthritis,Sjogren's, sarcoidosis etc.), and prior pneumonectomy.