GFRA4 and medullary thyroid gland carcinoma: In contrast, among the top upregulated genes, we found MTC/C cell-specific markers, such as CEA (CEACAM5 gene and its paralog, CEACAM6), calcitonin (CALCA gene and its paralog, CALCB), and genes related to neuroendocrine functions (CHGA, CHGB, and GRP), in agreement with previous reports [25,26,31], as well as the RET gene and its coreceptor, GFRA4, in agreement with its oncogenic activation.