Medullary thyroid carcinoma in a 6-year-old boy with previous Langerhans cell histiocytosis presenting high level of pro-calcitonin

Objectives: To describe medullary thyroid cancer (MTC) onset in a boy affected previously by Langerhans cell histiocytosis (LCH) and review the literature for other reports of this association. Case presentation: A 6-year-old boy was treated for LCH diagnosis when he was 4 years old. After treatment, a rise in procalcitonin levels was observed (2.36–2.78 ng/ml) initially interpreted as inflammatory response. Further procalcitonin increase (4.61 ng/ml) with cervical lymphadenopathy and no infective focus was suspicious of thyroid involvement, confirmed by ultrasound, serum calcitonin, and cytological diagnosis. Total thyroidectomy with bilateral lymph node exeresis was performed. RET gene analysis revealed p.Met918Thr mutation. No association between the previous LCH and MTC had been identified to date. Conclusions: MTC is a rare condition in childhood presenting with an aggressive behaviour. It becomes crucial to increase the awareness of its features and anticipate diagnosis. Therefore, persistent high levels of pro-calcitonin without infective/inflammatory focus should lead to suspicion of thyroid involvement.