PTH and breast cancer: High levels of expression of calcium-sensing receptor (CaSR) have been reported in profiling studies of breast cancer gene expression in patients’ specimens as well as breast cancer cell lines specifically MCF-7 and MDA-MB-231 cells which has higher expression levels compared to nonmalignant breast cell lines.4-7 The CaSR is a class C/ G protein–coupled receptor that has a well-established physiologic role in regulating extracellular calcium levels and parathyroid hormone release.8