Phase 1b Trial of Dinaciclib With Pembrolizumab for Advanced Breast Cancer

PRIMARY OBJECTIVE: I. Define the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D) of dinaciclib SECONDARY OBJECTIVE: I. Evaluation of the preliminary efficacy of this combination using RECIST 1.1 and irRECIST. EXPLORATORY OBJECTIVE: I. Characterizing and correlating PDL-1 and MYC overexpression with clinical response. OUTLINE: This is an open-label phase Ib trial of weekly dinaciclib in combination pembrolizumab in participants with advanced triple negative breast cancer. Participants will undergo a single needle biopsy of a site of active disease prior to initiating treatment of Pembrolizumab and dinaciclib in 21 day cycles. The dose of dinaciclib will be escalated following a toxicity probability interval (TPI) design where dose-limiting toxicities (DLT) observed during the first cycle will be used to determine whether additional participants should be enrolled at the same, higher, or lower dose level. Treatment will continue until disease progression, intolerable toxicity, or participant withdraws consent. In the event of a complete response (CR), participants may elect to hold dinaciclib treatment and continue with pembrolizumab alone. At the time of radiographic disease progression, dinaciclib can be resumed at the same dose as at the time of discontinuation. Participants will be followed for 30 days after the last dose of treatment.