Objective: To determine the Overall Response Rate (ORR) to Imprime PGG + pembrolizumab in subjects with advanced melanoma or metastatic TNBC
Safety: To characterize the safety of Imprime PGG + pembrolizumab given in combination
Hypothesis: Restore (for melanoma) or enhance (for TNBC) sensitivity to checkpoint inhibitors (CPI) by appropriate and effective stimulation of the subject's innate and adaptive immune systems in those subjects who have failed 1st line therapy
The study will incorporate Simon's optimal 2-stage design with sample size fixed at 12 subjects each in Stage 1 for advanced melanoma and for Triple Negative Breast Cancer (TNBC) subjects. The safety criterion of ≤ 4 (or ≤ 33%) subjects with Grade 3/4 adverse events in Cycle 1 within either tumor type must be met in order to proceed to Stage 2. The starting dose is 4 mg/kg for Imprime PGG. In the event there are a total of > 4 (or > 33%) of subjects with Grade 3/4 adverse events in Cycle 1, the dose of Imprime PGG will be reduced to 2 mg/kg, and Stage 1 will be repeated at a dose of 2 mg/kg with an additional cohort of n=12 subjects. For the dose that meets the safety criterion in Stage 1, at least 1 response in melanoma subjects and 2 responses in TNBC subjects amongst the 12 subjects within each tumor type must be observed in order to proceed to Stage 2.
Stage 2 will enroll an additional 17 subjects with melanoma, and 30 subjects with TNBC. For the dose that meets the Stage 1 safety criterion, success will be declared if at least 4 amongst the total of up to 29 subjects with melanoma, and 13 amongst the total of up to 42 subjects with TNBC achieve an objective response.