APC and carcinoma: Second, a set of markers are down-regulated (e.g., APC, p27 protein, calcium-sensing receptor CaSR) or up-regulated (e.g., proliferation activity by Ki-67 exceeding 5%) in parathyroid carcinoma compared to benign parathyroid disease and thus can be helpful increasing the suspicion of malignancy and prompting the search for the definitive criteria for carcinoma.