Heterotopic SMARCB1-deficient high-grade transformed/dedifferentiated acinic cell carcinoma and sine-qua-non radiology- pathology with TNM challenge.

Heterotopic salivary tissue (HSGT) is found where salivary glands are not normally placed. HSGT manifests as accessory salivary glands, salivary tissue associated with branchial cleft anomalies, and true heterotopic salivary gland tissue. Benign and malignant salivary heterotopias have been described in the literature, with the most common reported neoplasm being Warthin tumor. In the malignant group, the most frequent tumors are mucoepidermoid carcinomas (MEC) and acinic cell carcinomas (AciCC). For the treating physician, this condition presents a diagnostic dilemma, whether these salivary heterotopias represent metastasis from orthotopic salivary origin or primary of heterotopic origin. We report a unique case of heterotopic high-grade/dedifferentiated SWI/SNF (SMARC-B1) deficient AciCC. A 48 yo male presented for evaluation of a persistently enlarged right sided lymph node for the past 6 months. A biopsy was performed, and initial interpretation was squamous cell carcinoma- p16 negative. Diffuse adenopathy and lack of an obvious primary source prompted a modified right neck dissection. Final pathological diagnosis was heterotopic SWI/SNF (SMARCB1)-deficient high-grade/dedifferentiated salivary AciCC. This case is an example of meticulous pathological investigation and multidisciplinary decision-making process of a heterotopic SMARCB1-deficient dedifferentiated AciCC. Heterotopic dedifferentiated AciCC are extremely rare (two cases reported so far), necessitating definitive surgery with neck dissection and adjuvant therapy. Long term outcomes are not known, and an adequate follow up is mandatory.