In humans, USP15 is highly expressed in endocrine tissues, the gastrointestinal tract, the liver, the gallbladder, bone marrow, lymphoid tissues, etc. (Figure 2).USP15 is upregulated in a variety of cancers, including glioblastoma [60], breast cancer [60], ovarian cancer [61], multiple myeloma [62], prostate cancer [63], gastric cancer [64,65], pancreatic ductal adenocarcinoma [66,67], and chronic myeloid leukemia [68]. Here, USP15 is linked to plasma cell myeloma.