Study of Neoadjuvant Imprime PGG and Pembrolizumab for Stage III, Resectable Melanoma

Approximately 50 ABA+ subjects with resectable, Stage III (IIIB, IIIC, or IIID) melanoma will be included in the study and randomized in a 3:2 ratio to neoadjuvant treatment with Imprime PGG plus pembrolizumab vs. pembrolizumab monotherapy. A baseline, reference biopsy and a PET/CT scan will be obtained prior to commencing 3 cycles (9 weeks) of neoadjuvant treatment with either regimen. During Week 5, subjects will provide another biopsy to assess treatment effects on the tumor and its microenvironment. At the completion of neoadjuvant treatment and before surgery, subjects will undergo another PET/CT scan to assess radiological and metabolic response compared to baseline. Subjects will then undergo surgical resection. A pre-surgical assessment of operability will be done by the responsible surgeon, and the investigator will ensure that adverse events occurring during the treatment period have resolved to the minimal acceptable level that would not place the subject at undue risk or delay surgery for more than 1 week after the last dose of Imprime or 3 weeks after last dose of pembrolizumab, when subjects will undergo surgical resection. The surgical specimen will be locally and centrally assessed by a pathologist to determine the pathological response (pCR, pMR, pPR) induced by the neoadjuvant treatment (central read will be blinded). Following surgery, subjects will be followed for safety for 90 days. The total duration of systemic treatment will be 3 cycles (9 weeks). In the Investigational arm, surgery should be performed no more than a week after the subject's last dose of Imprime PGG and in the Control arm, surgery should be performed within 3 weeks of the subject's last dose of pembrolizumab.