Necrotizing Sialometaplasia: A Benign Challenging Mimicker of Cancer in Mohs Surgery

Summary: Necrotizing sialometaplasia (NS) is a benign condition first described in the minor salivary glands of the soft palate, with morphological changes that can be misinterpreted as squamous cell carcinoma. Here, we report a case of NS involving the parotid gland, complicating Mohs resection in a patient with nodular-type basal cell carcinoma on the cheek. During the surgery, the clear deep margins could not be achieved, and the patient was referred to a surgeon for excision of the deep cutaneous tissue and parotid gland. The resection specimen revealed an ulcerated cutaneous lesion with no residual basal cell carcinoma but extensive squamous epithelial islands overlying the parotid gland. The squamous epithelium showed no atypia, and the presence of ducts within the islands was consistent with extensive NS. NS is a rare condition in salivary glands and its presence in cutaneous tissue poses a significant diagnostic challenge, especially during Mohs surgery, where cytologic features can be altered by frozen section artifacts. The evaluation of NS and the diagnostic clues to distinguish it from malignancies during Mohs surgery have not been reported before. Recognizing this entity is crucial as over-diagnosis and overtreatment of this benign condition as malignancy can lead to unnecessary interventions.