Mixed medullary and papillary thyroid carcinoma: a case report and literature review

Mixed medullary-papillary thyroid carcinoma (MMPTC) is a rare thyroid malignancy. We report a case in a 55-year-old Asian female who presented with bilateral thyroid nodules during a routine examination in December 2022. After three years of ultrasound (US) surveillance, a fine-needle aspiration cytology (FNAC) of the progressively suspicious left nodule in November 2025 confirmed papillary thyroid carcinoma (PTC, Bethesda VI) with a BRAF V600E mutation. Preoperative laboratory testing revealed a significantly elevated calcitonin (Ctn) level, suggesting concurrent medullary thyroid carcinoma (MTC). The patient subsequently underwent total thyroidectomy with bilateral dissection of level VI-VII cervical lymph nodes, plus right lateral (level II-V) cervical lymph node dissection. Postoperative pathology identified pure PTC in the left lobe and MMPTC in the right lobe, with metastatic PTC revealed in 3 of the 8 level VI-VII cervical lymph nodes. Levothyroxine sodium was administered postoperatively for TSH suppression, and Ctn levels normalized within one month. At the final follow-up in January 2026, the patient remained stable with normal Ctn levels. This case highlights that individualized preoperative Ctn testing, tailored to clinical context, may be beneficial for patients with FNAC-confirmed PTC. Such targeted screening may facilitate the detection of occult concurrent MTC and facilitate the selection of optimal surgical strategies. Management of MMPTC requires an individualized surgical strategy and postoperative plan based on the separate staging of both PTC and MTC components. Postoperatively, long-term follow-up assessment incorporating both serological and imaging findings is required.