This leads to increased bone resorption, creating a favorable niche for tumor cells to colonize and expand within the bone; in this study, it has been reported that in breast cancer, 90% of metastatic cells express PTHrP, while only 50% of cells of the primary tumor express it, underscoring the critical role of PTHrP in the skeletal involvement of breast cancer. The gene discussed is PTHLH; the disease is neoplasm.