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

De-identified individual patient data for variables necessary to address the specific research question in an approved data sharing request.

Data sharing requests relating to this study will be considered beginning 18 months after the study has ended and either 1) the product and indication have been granted marketing authorization in both the US and Europe or 2) clinical development for the product and/or indication discontinues and the data will not be submitted to regulatory authorities. There is no end date for eligibility to submit a data sharing request for this study.

Qualified researchers may submit a request containing the research objectives, the Amgen product(s) and Amgen study/studies in scope, endpoints/outcomes of interest, statistical analysis plan, data requirements, publication plan, and qualifications of the researcher(s). In general, Amgen does not grant external requests for individual patient data for the purpose of re-evaluating safety and efficacy issues already addressed in the product labelling. Requests are reviewed by a committee of internal advisors. If not approved, a Data Sharing Independent Review Panel will arbitrate and make the final decision. Upon approval, information necessary to address the research question will be provided under the terms of a data sharing agreement. This may include anonymized individual patient data and/or available supporting documents, containing fragments of analysis code where provided in analysis specifications. Further details are available at the URL below.