A Study to Evaluate Safety and Anti-Tumor Activity of Eciskafusp Alfa (RO7284755) Alone or in Combination With Atezolizumab in Participants With Advanced and/or Metastatic Solid Tumors

This is an entry-into-human study and will assess the effects of eciskafusp alfa (RO7284755) as a single agent and in combination with atezolizumab in adult participants with solid tumors considered responsive to checkpoint inhibition blockade. The maximum duration in the study for each participant will be up to 28 months.

The study consists of three parts: dose-escalation of eciskafusp alfa as a single agent (Part 1), dose-escalation of eciskafusp alfa in combination with atezolizumab (Part 2), and extension of eciskafusp alfa as a single agent and/or in combination with atezolizumab (Part 3).

Eligibility Criteria:
Inclusion Criteria:

* Locally advanced/unresectable or metastatic disease
* No standard of care (SoC) (approved) treatments are available for the participant, or the participant cannot tolerate such treatments
* Measurable disease, as defined by Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1)
* Eastern Cooperative Oncology Group Performance Status 0 to 1
* Life expectancy of \>=12 weeks
* Consent to provide an archival tumor tissue sample
* Adequate cardiovascular, hematological, coagulative, hepatic and renal function

Exclusion Criteria:

* Rapid disease progression or suspected hyperprogression or threat to vital organs or critical anatomical sites requiring urgent alternative medical intervention
* Untreated central nervous system (CNS) metastases
* Treated asymptomatic CNS metastases
* Spinal cord compression not definitively treated with surgery and/or radiation or previously diagnosed and treated spinal cord compression without evidence that disease has been clinically stable for \>= 2 weeks before Cycle1 Day 1 (C1D1)
* Active or history of carcinomatous meningitis/leptomeningeal disease
* Uncontrolled tumor-related pain or symptomatic hypercalcemia
* Concurrent second malignancy
* Evidence of significant, uncontrolled concomitant diseases that could affect compliance with the protocol or interpretation of results
* Episode of significant cardiovascular/cerebrovascular acute disease within 28 days before study treatment administration
* Active or uncontrolled infections
* Known HIV infection
* Hepatitis B virus (HBV) or hepatitis C virus infection
* Adverse events related to any prior radiotherapy, chemotherapy, targeted therapy, CPI therapy or surgical procedure must have resolved to Grade \<=1, except alopecia Grade 2 peripheral neuropathy, and hypothyroidism and/or hypopituitarism on a stable dosage of hormone replacement therapy
* Participants with bilateral pleural effusion
* Major surgery or significant traumatic injury \< 28 days before study treatment administration or anticipation of the need for major surgery during study treatment
* Known allergy or hypersensitivity to any component of the formulations of the IMPs to be administered, including but not limited to hypersensitivity to Chinese hamster ovary cell products or other recombinant or humanized antibodies
* History of severe allergic anaphylactic reactions to chimeric, human or humanized antibodies, or fusion proteins
* Previous treatment with Interleukin-2 (IL-2)/Interleukin-5 (IL-15)-like cytokines. IL-2/IL-15 use as an adjunct treatment component for adoptive cell therapy is permitted. In Part 3, patients who have received adoptive cell therapy such as tumor-infiltrating lymphocytes (TIL) are excluded.