CD38 and plasma cell myeloma: The advent of anti‐CD38 monoclonal antibodies (MoABs) has led a new relapsed or refractory multiple myeloma (RRMM) population to emerge in recent years encompassing patients pre‐exposed to at least one proteasome inhibitors (PI), one immunomodulatory agent (IMiD), and an anti‐CD38 MoAB, separately or in combination (hereafter referred to as ‘triple‐class exposed’).