As INPP4B levels are significantly decreased in various cancers, it has first been described as a tumor suppressor gene, e.g., in prostate, basal-like breast, ovarian, cervical, gallbladder, and gastric cancer [21, 24–29], as well as thyroid neoplasm [30] and multiple myeloma [31]. This evidence concerns the gene INPP4B and plasma cell myeloma.