Lymph node metastases in pediatric medullary thyroid carcinoma.

Background: Unlike medullary thyroid carcinoma in adults, the vast majority of pediatric medullary thyroid carcinoma is hereditary. Pediatric medullary thyroid carcinoma is known to have different genetic alterations driving tumorigenesis, but it is not known if pediatric medullary thyroid carcinoma has different clinicopathologic features. This study aims to identify which pediatric medullary thyroid carcinoma patients might warrant elective neck dissection.

Methods: We selected all patients ages 0 to 19 diagnosed with clinically evident medullary thyroid carcinoma in the National Cancer Database between 2004 to 2016. Clinicopathologic factors, treatments, and outcomes were analyzed and compared between this cohort and adults (ages ≥20) with medullary thyroid carcinoma.

Results: One hundred twenty-five pediatric medullary thyroid carcinoma (median age: 13) and 5,086 adult medullary thyroid carcinoma (median age: 57) patients were identified. Pediatric patients had smaller tumors (median diameter: 1.2 cm vs 2.0 cm; P < .001), lower rates of nodal metastases (n = 31, 36.9% vs 1,689, 50.4%; P = .02) but double the incidence of multifocal tumors (n = 70, 59.3%, vs 1,412, 29.9%; P < .001) compared with adults. Multifocal tumors conferred a significantly increased risk of nodal metastases in adult medullary thyroid carcinoma (64.4% vs 43.2%; P < .001) but not pediatric medullary thyroid carcinoma (37.7% vs 35.7%; P = .85). Nodal metastases were more frequent among older children (0-5 years: 0.0%, 6-12: 40.7%, 13-19: 41.7%; P = .04). However, rates of occult nodal metastases were similar between older children (6-19 years: n = 12, 21.4%) and adults (557, 25.8% P = .56).

Conclusion: Pediatric medullary thyroid carcinoma has lower rates of lymph node metastases compared with adults. The risk of nodal disease was low among the youngest children, but older children ages 6 to 19 were at considerable risk for occult metastases. These findings could guide clinicians in selecting pediatric patients considered for elective lymph node dissection.