In patients with humoral hypercalcemia of malignancy (HHM), serum levels of 1,25-dihydroxyvitamin D (1,25(OH)2D) are generally low, although the pathophysiology of the impaired vitamin D metabolism is not fully understood. In the present study, we have investigated vitamin D metabolism in our newly developed rat model of HHM in which a human infantile fibrosarcoma producing parathyroid hormone-...