Since a majority of all breast cancer cases (about 70–80%) are hormone receptor-positive (HR+)27, we investigated PMCA4 protein abundance in HR+ breast carcinoma tissue samples (Supplementary Data) using the PMCA4-specific antibody JA9 (JA9 does not discriminate between PMCA4 “a” and “b” splice variants)28, and compared the results to those of normal breast tissue samples obtained after breast reduction surgery. The gene discussed is ATP2B4; the disease is breast cancer.