RPN2 and breast cancer: Downregulation of ribophorin II has been reported to inhibit cancer cell proliferation and metastasis in osteosarcoma (Fujiwara et al., 2014), lung cancer (Fujita et al., 2013; Fujita et al., 2015), and breast cancer (Takahashi et al., 2013; Tominaga et al., 2014).