Radiation-Induced Second Primary Gingival Squamous Cell Carcinoma Developing 26 Years After Radiotherapy for Nasopharyngeal Carcinoma: A Case Report.

Radiation-induced second primary oral squamous cell carcinoma is a rare but recognized late complication of radiotherapy for nasopharyngeal carcinoma, typically presenting after a prolonged latency period within previously irradiated tissues. A 79-year-old woman developed a moderately differentiated squamous cell carcinoma involving the left edentulous mandibular gingiva and alveolar ridge 26 years after radiotherapy for nasopharyngeal carcinoma, with no history of tobacco or alcohol use. The patient had severe xerostomia and other chronic post-radiotherapy oral complications. Clinical examination revealed an irregular erythroleukoplakic lesion with ulceration, and histopathology confirmed the diagnosis. Surgical excision was performed without clinical or radiographic evidence of bone invasion, and additional radiotherapy was avoided because of the patient's prior head and neck radiotherapy and severe post-radiotherapy tissue changes. The patient remained disease-free after 15 months of follow-up. This case highlights a rare edentulous mandibular gingival/alveolar ridge presentation of radiation-induced second primary oral squamous cell carcinoma with an unusually long latency period. Persistent gingival or alveolar ridge lesions in previously irradiated tissues may be misinterpreted as traumatic, inflammatory, or post-radiotherapy changes; therefore, lifelong oral surveillance and early biopsy of suspicious lesions are essential in previously irradiated patients.