Orphan G-protein-coupled receptor family C group 5 member D (GPRC5D) has seven transmembrane segments forming the core of the receptor, as well as an intracellular C-tail and an extracellular N-terminal domain. GPRC5D is highly and selectively expressed on the surface of CD138+ multiple myeloma (MM) cells, whereas in normal tissues, a much lower expression is limited to plasma cells and certain hard keratinizing tissues. This makes GPRC5D a promising marker for monitoring tumor load and a target antigen for MM-specific T cell-engaging therapies such as bispecific antibodies and CAR-T cells.