A Study of HST-1011 Given as Monotherapy and in Combination With an Anti-PD1 Antibody

Key Inclusion Criteria:

* Patient is at least 18 years of age.
* Patient is capable of understanding and complying with protocol requirements.
* Patient has signed and dated ICF.
* Patient has a histologically confirmed, advanced solid tumor (metastatic, recurrent, and/or unresectable) in one of the following categories: 1) anti-PD-(L)1 relapsed/refractory; 2) platinum-resistant ovarian cancer; 4) anal cancer; 5) rectal cancer; or 6) castration-resistant prostate cancer
* Patient has failed prior standard of care therapies appropriate for their metastatic disease.
* Patient has at least 1 measurable non-central nervous system (CNS) lesions per RECIST 1.1.
* Patient has provided consent for pre- and on-treatment biopsies.
* Eastern Cooperative Performance Status of 0 or 1.

Key Exclusion Criteria:

* Patient has active autoimmune disease or other medical conditions requiring chronic systemic steroid therapy at the time of screening.
* Patient has an unacceptable intolerance to anti-PD-(L)1 monoclonal antibody (Part B Only).
* Patient has previously participated in a clinical study evaluating a CBL-B inhibitor.
* Patients has untreated and/or symptomatic metastatic CNS disease.
* Patient is currently taking any concomitant medications at Screening that have the potential to cause a clinically relevant drug-drug interaction with HST-1011.
* Patients with a history of gastrointestinal disease that may affect absorption of the study drug, or patients who are not able to take oral medications.
* Patient has an active infection requiring systemic therapy.
* Patient has known or suspected infection with SARS-CoV-2 virus.