PD-1/PD-L1 inhibitors in multiple myeloma: The present and the future.

The introduction of PD-1/PD-L1 pathway inhibitors has marked a significant milestone in the treatment of various types of solid tumors. The current situation in multiple myeloma (MM) is rather unclear, as distinct research groups have reported discordant results. This discrepancy dominantly concerns the expression of PD-1/PD-L1 molecules as well as the identification of the responsible immune effector cell population. The results of monotherapy with PD-1/PD-L1 inhibitors have been unsatisfactory in MM, suggesting that a combination approach is needed. The most logical partners are immunomodulatory agents as they possess many synergistic effects. We are also proposing other rational and promising combinations (e.g., daratumumab, ibrutinib, anti-CD137) that warrant further investigation.