A Study of PHST001 in Advanced Solid Tumors

Key Inclusion Criteria: * Histologically or cytologically confirmed advanced solid tumor which has relapsed from 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 site Investigator/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 treatment has been completed, with no evidence of malignancy for 5 years. Participants with basal cell carcinoma of the skin, Stage I melanoma, melanoma in situ, squamous cell carcinoma of the skin, early-stage prostate cancer, or carcinoma in situ, excluding carcinoma in situ of the bladder, who have undergone potentially curative therapy are not excluded and can be enrolled regardless of disease-free period following completion of potentially curative therapy. Participants with early-stage breast cancer who have undergone curative intent treatment and with no disease recurrence for 2 years after treatment are not excluded. * Active known CNS metastases and/or carcinomatous meningitis. Participants with previously treated CNS metastases may participate provided they are radiologically stable (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 days prior 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 study treatment. Participants must have recovered from all AEs due to previous therapies to Grade ≤1 or baseline. Participants with Grade ≤2 neuropathy may be eligible. Participants with endocrine-related AEs Grade ≤2 requiring treatment or hormone replacement may be eligible. * Prior autologous or allogeneic hematopoietic stem cell transplant or solid organ transplant. * Received previous treatment with another agent targeting CD24.