NR4A1 and breast cancer: 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.