A 16-year-old patient (patient 19, Table 3) with a RET 918 MTC presented with locally advanced disease and painful extensive bone involvement with disproportionately elevated CEA to calcitonin levels, 79 pg/mL and 4999 ng/mL, respectively; suggesting disease dedifferentiation. The gene discussed is CALCA; the disease is medullary thyroid gland carcinoma.