XIAP and plasma cell myeloma: WT161 has been regarded as a remarkable anti-tumor agent for several types of cancers, including multiple myeloma (Hideshima et al., 2016; McClure et al., 2018; García-Guerrero et al., 2021), breast cancer (Hideshima et al., 2017), osteosarcoma (Sun et al., 2021), and retinoblastoma (Sun et al., 2019) by affecting the regulation of CD38, growth factor receptors, PTEN, or X-linked inhibitor of apoptosis protein (XIAP) in tumor cells.