Background and purpose: Medullary thyroid carcinoma (MTC) is a rare disease in children and adolescents

which is seldom reported in China. The purpose of this study was to explore its clinicopathological features

diagnosis and prognostic factors

and to improve the understanding of MTC. Methods: Data of 10 cases of MTC in children and adolescents were collected from Fujian Cancer Hospital from January 2007 to May 2021

and clinical features

morphology

immunophenotype

gene mutation

and outcome were analyzed. Results: There were 6 sporadic cases

and 4 cases with family history

aged 10-20 years with a mean of 17 years. All showed elevated serum calcitonin (CT) and carcinoembryonic antigen (CEA). Bilateral thyroid lesions were found in 9 patients. The tumor diameter was 0.2-3.5 cm

with a median diameter of 1.5 cm. Microscopically

the tumor presented a patchy

nest- shaped

or beamlike distribution

with invasive growth pattern and surrounding satellite nodules. Papillary and follicular structures were also observed in some cases. The cells were round and oval

mixed with some spindle cells and plasmacytoid cells. A few giant cells and intranuclear pseudo-inclusions were also found. Different degrees of fibrosis/amyloid deposition were observed in the tumor stroma

with occasional calcification and sand bodies. Synaptophysin (Syn)

chromogranin A (CgA)

cluster of differentiation (CD56)

CT

CEA

thyroid transcription factor-1 (TTF-1) and Congo red staining were positive for tumor cells

while thyroglobulin (Tg) was negative. The M918T mutation in RET gene was the most common genetic change in MTC. Among all of the 10 cases

the serum CT and CEA of 8 cases were reduced to normal levels after operation

without recurrence/metastasis (biochemical cure) during the follow-up period (27-98 months

with an average of 62 months). One patient was non-biochemical cure

and cervical lymph node dissection was performed twice at 75 and 108 months postoperatively. Another patient died of tumor 6 months after surgery

which presented high-grade nuclei (polymorphic

prominent nucleoli

mitotic  ＞ 3/10HPF)

high proliferation index (Ki- 67 was 20%)

numerous intravascular tumor thrombi and focal coagulant necrosis. Conclusion: The majority of MTC in children and adolescents have bilateral thyroid involvement. Bilateral thyroidectomy is the best therapeutic theatment for removing potential hidden lesions and prevent recurrence. The elevation of serum CT and CEA is an important clinical feature. High nuclear grade

high Ki-67 proliferation index

intravascular tumor thrombus and necrosis are important prognostic indicators.