While calcitonin expression was generally consistent among MTC, the discordant results between IHC and transcript expression in the TC1020 specimen could be attributed to intratumor heterogeneity as different tumor tissue samples were used for IHC and genomic analyses, or less likely, rapid release and/or degradation of calcitonin by tumor cells prior to fixation9. The gene discussed is CALCA; the disease is medullary thyroid gland carcinoma.