A Study of PHST001 in Advanced Solid Tumors

Key Inclusion Criteria:

• Histologically or cytologically confirmed advanced solid tumor which has relapsedfrom or been refractory to all locally available standard therapies.

• Adequate organ function per laboratory testing

• Pregnancy prevention requirements

• Measurable disease per RECIST v1.1 (or RANO) as assessed by the local siteInvestigator/radiology

• Performance status of 0 or 1 on Eastern Cooperative Oncology Group (ECOG) scale

Key Exclusion Criteria:

• Diagnosis of immunodeficiency

• History of a previous additional malignancy, unless potentially curative treatmenthas been completed, with no evidence of malignancy for 5 years. Participants withbasal cell carcinoma of the skin, Stage I melanoma, melanoma in situ, squamous cellcarcinoma of the skin, early-stage prostate cancer, or carcinoma in situ, excludingcarcinoma in situ of the bladder, who have undergone potentially curative therapyare not excluded and can be enrolled regardless of disease-free period followingcompletion of potentially curative therapy. Participants with early-stage breastcancer who have undergone curative intent treatment and with no disease recurrencefor 2 years after treatment are not excluded.

• Active known CNS metastases and/or carcinomatous meningitis. Participants withpreviously treated CNS metastases may participate provided they are radiologicallystable (i.e., without evidence of progression for at least 2 weeks by repeat imaging [note that the repeat imaging should be performed during study screening]),clinically stable, and without requirement of steroid treatment for at least 14 daysprior to the first dose of study treatment.

• Received prior systemic anticancer therapy including investigational agents within 21 days or, if shorter, within 5 half-lives prior to the first dose of studytreatment. Participants must have recovered from all AEs due to previous therapiesto Grade ≤1 or baseline. Participants with Grade ≤2 neuropathy may be eligible.Participants with endocrine-related AEs Grade ≤2 requiring treatment or hormonereplacement may be eligible.

• Prior autologous or allogeneic hematopoietic stem cell transplant or solid organtransplant.

• Received previous treatment with another agent targeting CD24.