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 2 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, low grade neoplasms, 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 from a systemic (non-CNS) primary malignancy. Participants with previously treated CNS metastases are eligible, provided they are radiologically and clinically stable (i.e., no evidence of progression for at least 2 weeks by repeat imaging performed during screening) and are not requiring systemic corticosteroids above the physiologic replacement for at least 7 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.