Symbiotic-GI-13: A Study to Learn About Study Medicine Called PF-08634404 as a Single Treatment and Combination Treatment in Adult Participants With a Liver Cancer Called Hepatocellular Carcinoma, That is Too Advanced to be Removed by Surgery and May Have Spread to Other Parts of the Body.

Inclusion Criteria:

* 18 years of age or older at screening.
* Locally advanced or metastatic HCC with diagnosis confirmed by histology/cytology or clinically by AASLD criteria (for patients with cirrhosis). Participants without cirrhosis require histological confirmation of diagnosis.
* Disease that is not amenable to curative surgical and/or locoregional therapies, or progressive disease after surgical and/or locoregional therapies.
* At least 1 measurable (as defined by RECIST 1.1 per investigator) and untreated lesion.
* Adequate hepatic, liver, and renal function
* No prior systemic therapy for HCC.
* ECOG performance status 0 or 1
* Child-Pugh Class A

Key Exclusion Criteria:

* Moderate or severe ascites.
* History of hepatic encephalopathy.
* Participants with known active CNS lesions, including leptomeningeal metastasis, brainstem, meningeal, or spinal cord metastases or compression.
* Clinically significant risk of hemorrhage or fistula.
* Participants with any history of another malignancy within 3 years.
* History of allogeneic organ transplantation and allogeneic hematopoietic stem cell transplantation.
* Participants with active autoimmune diseases requiring systemic treatment within the past 2 years.
* Clinically significant cardiovascular disease within 6 months prior to the first dose.
* Major surgery or severe trauma within 4 weeks prior to the first dose or planned major surgery during the study.
* History of severe bleeding tendency or coagulation dysfunction.
* History of severe ulcers, unhealed wounds, gastrointestinal perforation, abdominal fistula, gastrointestinal obstruction, intra-abdominal abscess, or acute gastrointestinal bleeding, including bleeding event due to esophageal and/or gastric varices, within 6 months prior to the first dose.
* Participants with acute, chronic or symptomatic infections.
* Participants with history of immunodeficiency.