Phase Ib Study of AlpeliSib With PEmbroLizumab in Patients With mEtastatic Breast caNcer or melanomA (SELENA)

To find a recommended dose of the combination of alpelisib and pembrolizumab that can be given to patients with metastatic breast cancer or melanoma.

Inclusion Criteria: 1. Patients must be 18 years or older. 2. Patients must be willing and able to provide informed consent. 3. In the dose escalation, patients must have histologically documented locally advanced, unresectable, or metastatic melanoma or TNBC that has progressed on treatments that are known to prolong survival or for which no standard treatment is available or refused such therapy. Presence of active brain metastases is not required. Patients with active metastases as defined below can be eligible in the dose escalation. 4. In the dose expansion, patients must have histologically documented locally advanced, unresectable, or metastatic melanoma or TNBC that has progressed on treatments that are known to prolong survival or for which no standard treatment is available or refused such therapy. 1. Melanoma patients without brain metastases who have progressed on an anti-PD-1 or anti-PD-L1-based regimen. 2. Melanoma patients with active and untreated brain metastases who have progressed on an anti-PD-1 or anti-PD-L1-based regimen. 3. TNBC patients (defined as ER \