Phase 1/1b/2 Study of Oral PMD-026 in Patients With Metastatic Breast Cancer

Inclusion Criteria, Combination with fulvestrant (Part 3):

* RSK2 positive from available archival or fresh tumor tissue (FFPE).
* Histologically or cytologically diagnosed HR+, HER2-
* ESR1 wild type
* Diagnosis of adenocarcinoma of the breast with evidence of either locally advanced disease not amendable to resection or radiation with curative intent or metastatic disease not amendable to curative therapy
* Must be appropriate candidates for endocrine therapy
* Previously received at least 1 line of endocrine therapy for MBC or had recurrence while on adjuvant endocrine therapy for locally advanced breast cancer
* Discontinued endocrine therapy at least 15 days prior to first dose of PMD-026
* At least 1 measurable target lesion as defined by RECIST v1.1
* Progression on or after treatment with a CDK4/6 inhibitor in combination with endocrine therapy inhibitor in the locally advanced or metastatic setting
* Adequate hematologic, hepatic, and renal function as assessed by laboratory parameters
* Toxicity related to prior therapy resolved to at least Grade 1 (alopecia excepted) or to at least Grade 2 with prior approval of the Medical Monitor

Exclusion Criteria, Combination with fulvestrant (Part 3):

* Prior chemotherapy
* ESR1 mutations
* ≤14 days from biological or investigational therapy
* Presence of visceral crisis or uncontrolled visceral disease for which chemotherapy would be indicated
* Central nervous system metastases, unless appropriately treated and neurologically stable
* History of leptomeningeal metastases
* Active, uncontrolled bacterial, viral, or fungal infection(s) requiring systemic therapy
* Known hepatitis B or hepatitis C infection
* Known HIV-positive with CD4+ cell counts \<350 cells/μL
* Known HIV-positive with a history of an AIDS-defining opportunistic infection
* History of clinically significant cardiovascular abnormalities, including QTcF interval \>460 msec (using Fridericia's formula)