CYP27B1 and Hypercalcemia: To our best knowledge, there are fewer than 5 reported cases of metastatic pNET resulting in hypercalcemia from excess 1,25-dihydroxyvitamin D. In the 2019 report from van Lierop et al, they were able to demonstrate expression of CYP27B1 in tumoral tissue mRNA, which encodes the converting enzyme (25-hydroxyvitamin D3 1-alpha-hydroxylase) that converts 25-hydroxyvitamin D3 into the active metabolite.