PTHLH and neuroendocrine neoplasm: Humoral mechanisms include the secretion of parathyroid hormone-related protein (PTHrP) or extrarenal 1,25 dihydroxy vitamin D (calcitriol). PTHrP can be secreted by squamous cell carcinoma, breast cancer, renal carcinoma, prostate cancer, melanoma, and neuroendocrine tumors.