Primary Small Cell Neuroendocrine Carcinoma of the Sublingual Gland Treated With Definitive Chemoradiotherapy: A Case Report.

Primary sublingual gland small cell neuroendocrine carcinoma (SCNEC) is extremely rare, with only one prior case reported, and no site-specific standard of care has been established. We report a case of primary sublingual gland SCNEC treated with definitive concurrent chemoradiotherapy (CRT). A 69-year-old man presented with a 21 × 15-mm right sublingual mass showing fluorodeoxyglucose uptake (SUVmax 9.9) on PET/CT. No nodal or distant disease was found. Biopsy revealed small cell morphology positive for INSM1/synaptophysin and pan-cytokeratin, with a high Ki-67 index (> 95%). IMRT delivered 70 Gy in 35 fractions to the primary tumor with elective bilateral nodal irradiation (levels I-V, 46 Gy). Cisplatin (80 mg/m2; day 1) and etoposide (100 mg/m2; days 1-3) were administered every 3 weeks for four cycles. Grade 3 oral mucositis and grade 2 neutropenia resolved. At 24 months post-CRT, the patient remains disease-free with preserved daily function. Definitive concurrent CRT appears to be a feasible and effective organ-preserving treatment option for limited-stage primary sublingual gland SCNEC, with durable disease control at 24 months in this case.