Elevated XBP1s expression is observed in many human tumors, including breast cancer (Davies et al. 2008; Chen et al. 2014), pancreatic adenocarcinomas (Romero-Ramirez et al. 2009), multiple myeloma (Carrasco et al. 2007), chronic lymphocytic leukemia (CLL) (Krysov et al. 2014), and plasma cell malignancy (Maestre et al. 2009), suggesting that Xbp1 is a proto-oncogene. Here, XBP1 is linked to plasma cell myeloma.