Study to Explore the Safety, Tolerability, and Pharmacokinetics of AMG 305 in Subjects With Advanced Solid Tumors

The primary objective of this study is to: * Evaluate the safety and tolerability of AMG 305 in adult participants * Determine the optimal biologically active dose (OBD), at or below the maximum tolerated dose (MTD) with MTD 1 as the maximum tolerated starting dose and MTD 2 as the maximum tolerated target dose * Determine the recommended phase 2 dose (RP2D)

Key Inclusion Criteria: * Participant has provided informed consent to the main study prior to initiation of any study specific activities/procedures * Male or female participants age ≥ 18 years * Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1 * Participants with histologically or cytologically documented selected solid tumor diseases. Participants must have exhausted available standard of care (SOC) systemic therapy or must not be candidates for such available therapy * For dose expansion cohorts: participants with at least 1 measurable lesion ≥10 mm which has not undergone biopsy within 3 months of screening scan. This lesion cannot be biopsied at any time during the study * Life expectancy \> 3 months * Adequate organ function Key Exclusion Criteria: * Untreated central nervous system (CNS) metastases, leptomeningeal disease, or spinal cord compression * History of other malignancy within the past 2 years * Ongoing or active infection (including chronic or localized) * Any pleural effusion or pericardial effusion within 4 weeks or ascites requiring recurrent drainage procedures or other medical intervention within 2 weeks prior to the first dose of the investigational products. * Known interstitial lung disease * Positive test for human immunodeficiency virus (HIV) * Positive hepatitis B surface antigen or positive hepatitis C virus ribonucleic acid (RNA) by polymerase chain reaction (PCR) * History of non-infectious/immune-checkpoint inhibitor related pneumonitis that required corticosteroids, or current or suspected pneumonitis that cannot be ruled out by imaging at screening. * Anticancer therapies including radiotherapy (with the exception of palliative radiation) chemotherapy or molecularly targeted treatments or tyrosine kinase inhibitors (TKI) within 4 weeks of administration of the first dose of AMG 305; checkpoint inhibitor therapy within 3 months of the first dose of AMG 305; or other immunotherapies/monoclonal antibodies within 3 weeks of administration of the first dose of AMG 305. * Has had a major surgery within 4 weeks of administration of a first dose of study treatment * Autoimmune disorders requiring chronic systemic steroid therapy or any other form of immunosuppressive therapy while on study (eg, ulcerative colitis, Crohn's disease) * Live and/or live-attenuated vaccines received within 28 days (or longer, if required locally) prior to the first dose of AMG 305 * Participants with unresolved toxicities from prior anti-tumor therapies to Common Terminology Criteria for Adverse Events (CTCAE) version 5.0 grade 1 or better, with the exception of alopecia and grade 2 peripheral neuropathy, which has been unchanged within the last 2 months and there is agreement to allow by both the investigator and sponsor * Currently receiving treatment in another investigational device or drug study * Female participants of childbearing potential or male participants unwilling to use protocol specified method of contraception * Females who are pregnant, breastfeeding or who plan to breastfeed or become pregnant while on study * History or evidence of any other clinically significant disorder, condition, or disease (with the exception of those outlined above) that, in the opinion of the investigator or Amgen physician, if consulted, would pose a risk to participant safety or interfere with the study evaluation, procedures or completion