Adenoid cystic carcinoma (ACC) is a rare, indolent, but locally aggressive salivary gland malignancy characterized by high rates of locoregional recurrence and late-stage distant metastasis. This report presents a 40-year-old male tobacco chewer with pT4a submandibular ACC featuring significant mandibular infiltration. Diagnostic evaluation using contrast enhanced Magnetic Resonance Imaging (CE-MRI) and fine needle aspiration cytology (FNAC) guided a radical multimodality approach. The patient underwent a left composite resection, including segmental mandibulectomy and modified radical neck dissection. For reconstruction, a pectoralis major myocutaneous (PMMC) flap was used to address the extensive surgical defect. Final histopathology identified the mixed cribriform and tubular growth pattern with negative margins and, notably, an absence of perineural invasion. Following surgery, the patient received 60 Gy of adjuvant radiation therapy. At the six-month follow-up, he remains clinically and radiologically disease-free with adequate functional recovery. This case highlights the necessity of radical surgical intervention for advanced ACC and the critical role of multimodality management. Due to the inherent risk of delayed recurrence, long-term clinical surveillance and standardized functional assessments are essential for optimal long-term outcomes.

Keywords: Adenoid Cystic Carcinoma, Submandibular Gland, Mandibulectomy, Composite Resection, Neck Dissection.