Microsecretory Adenocarcinoma of the Buccal Mucosa: A Rare Case Report and Review of Literature.

Microsecretory adenocarcinoma is a recently recognized low-grade salivary gland malignancy characterized by distinct histomorphological features, a specific immunophenotype, and recurrent MEF2C::SS18 gene fusion. This report describes 43-year-old woman with a two-decade history of a right buccal mucosa mass that exhibited recent enlargement, causing functional impairment. Surgical excision revealed a well-demarcated tumor with microcystic and tubular architecture, basophilic luminal secretions, and low proliferative activity (<1 mitotic figure/2mm2). Immunohistochemistry demonstrated positivity for S-100, SOX10, keratin 7, and p63, with negativity for p40, while fluorescence in situ hybridization confirmed SS18 rearrangement. No adjuvant therapy was administered, and the patient remained recurrence-free during a 3-year follow-up. This tumor confirms the slow-growing nature of microsecretory adenocarcinoma, emphasizes the importance of molecular testing for diagnosis, and clarifies the diagnostic differences between microsecretory adenocarcinoma and similar-looking salivary gland tumors.