PTHLH and Hypercalcemia: Lastly, treating tumor-bearing Tet-PTHrP;PyMT mice with anti-PTH1R antibodies corrects hypercalcemia but does not reverse STAT5 activation or reduce the expression of secretory markers, demonstrating that secreted PTHrP does not act systemically or on non-tumor cells in the microenvironment to induce paracrine cascades supporting secretory differentiation.