A Study of MT-303 in Adults With Advanced or Metastatic GPC3-Expressing Cancers, Including HCC

Inclusion Criteria * Aged 18 years or older * Histological diagnosis of advanced/recurrent or metastatic and/or unresectable HCC. \[Note: participants with other tumor types expressing GPC3 may be eligible for Module 1 pending a discussion with the Medical Monitor. Only participants with HCC are eligible for Module 2. * Measurable lesion per RECIST 1.1 criteria * Eastern Cooperative Oncology Group (ECOG) performance status grade of 0 or 1 * Child-Pugh score: Class A * Adequate organ function General Exclusion Criteria * Known active CNS metastasis and/or carcinomatous meningitis. * Any acute illness including active infection * History of liver transplantation or on waiting list * Participants with untreated or incompletely treated varices with bleeding or high risk for bleeding * Uncontrolled pleural effusion, pericardial effusion, or ascites * History of symptomatic congestive heart failure * History of chronic or recurrent (within the last year) severe autoimmune or immune mediated disease requiring steroids or other immune-suppressive treatments. Additional Module 2 Exclusion Criteria: * Known fibrolamellar HCC, sarcomatoid HCC, or mixed cholangiocarcinoma and HCC. * Significant cardiovascular disease * History of severe hypersensitivity to atezolizumab and/or bevacizumab. * History of idiopathic pulmonary fibrosis * Prior history of hypertensive crisis or hypertensive encephalopathy.