We present an unusual case of calcitonin-negative MTC arising in a “burnt out” thyroid where the only remaining significant cellular elements included putative UBB remnants, C-cell hyperplasia/medullary microcarcinomas (CCH/MMC), and MTCs, which were all MTC classifier positive according to ThyroSeq®. Here, CALCA is linked to medullary thyroid gland carcinoma.