Time frame: Pre-treatment (0-30 days before first ATRA administration) and post-treatment (84-130 days after first ATRA administration)
Anti-tumor activity will be determined by the percent change in MDSC (immunosuppressive myeloid-derived suppressor cells) frequency in peripheral blood of advanced melanoma patients undergoing the combined treatment of pembrolizumab and All-Trans Retinoic Acid (ATRA). Pre-treatment levels will be compared to post-treatment levels, where post-treatment means 4-6 weeks after stopping ATRA. MDSCs include CD45+, CD3-, CD19-, CD56-, CD11b+, CD33+, and HLA-DR-/low.
In the original protocol, suppressive function was included as part of this outcome measure to assess anti-tumor activity. However, this analysis could not be performed because the decrease in concentration of MDSCs after treatment resulted in inadequate data for the planned assays.