Clinicopathological discordance in retromolar trigone squamous cell carcinoma with repeated benign biopsies: a case report

Retromolar trigone (RMT) squamous cell carcinoma is an uncommon but highly aggressive oral cavity malignancy owing to its concealed anatomical location and propensity for early invasion of adjacent structures. Diagnosis may be challenging when superficial biopsies fail to detect underlying malignancy, resulting in delayed definitive treatment. A 67-year-old man with a history of tobacco use presented with a two-year history of a persistent non-healing ulcer involving the left retromolar trigone (RMT). Initial biopsies performed elsewhere revealed lichen planus and mild epithelial dysplasia. Despite progressive enlargement of the lesion and worsening pain, multiple repeat biopsies, including incisional, CT-guided bone, and ultrasound-guided soft-tissue biopsies, consistently demonstrated pseudoepitheliomatous hyperplasia and granulation tissue without evidence of invasive carcinoma. However, contrast-enhanced computed tomography (CECT) demonstrated a left RMT lesion with mandibular destruction and extension into the masticator space, corresponding to a clinical stage of cT4b cN0 cM0 based on preoperative clinical examination and CECT of the neck and thorax. Owing to persistent clinicoradiological suspicion of malignancy, the patient underwent wide local excision with segmental mandibulectomy and pectoralis major myocutaneous (PMMC) flap reconstruction. Intraoperative frozen-section examination demonstrated only benign inflammatory changes; however, definitive histopathological examination of the resected specimen confirmed well-differentiated keratinizing squamous cell carcinoma with mandibular invasion (pathological stage pT4a pNx). The patient subsequently received postoperative adjuvant concurrent chemoradiotherapy followed by triple oral metronomic therapy. Following completion of chemoradiotherapy, a post-treatment PET-CT demonstrated no evidence of residual or recurrent disease. The patient subsequently underwent monthly clinical follow-up and remained free of clinically evident locoregional recurrence at six months after surgery. This case highlights the importance of recognizing persistent clinicopathological discordance in suspicious retromolar trigone lesions. When repeated biopsy results remain inconsistent with the clinical and radiological findings, continued multidisciplinary evaluation and repeat tissue sampling are essential to avoid diagnostic delay and facilitate timely definitive management. The patient remains under active postoperative surveillance, and longer follow-up is required before conclusions regarding long-term oncological outcomes can be drawn.