The other applications of immunohistochemistry in parathyroid disease (Figure 1) include pathogenetic studies (e.g., expression of cyclin D1 or PD-L1, or the cellular composition and molecular characteristics of the tumour microenvironment); ability of certain proteins and panels to distinguish between benign and malignant parathyroid tumours; and histogenetic differential diagnostic considerations (e.g., thyroid vs. parathyroid origin). The gene discussed is CCND1; the disease is parathyroid gland disorder.