Carcinoma Ex-Pleomorphic Adenoma: Malignant Transformation Under Long-Term Surveillance

INTRODUCTION: Pleomorphic Adenomas (PA) of the salivary glands are usually found in the larger parotid and submandibular glands (SMG). The vast majority of these have a benign natural history. Approximately 25% of these tumors have the potential to undergo the adenoma-carcinoma sequence, whereby they lose important tumor suppressors such as APC, KRAS, TP53 and FGF and degenerate into invasive neoplasms. CASE DESCRIPTION: An 84-year old man presented to our clinic with a past medical history of smoking, temporal-mandibular joint pain, and enlargement of right SMG with recurrent episodes of sialadenitis. He had previously been diagnosed with an incidental right SMG PA a few years ago, for which he was being observed by serial imaging. He now developed a secondary painful mobile nodule adjacent to the right SMG. Contrast enhanced Head CT scan revealed the new mass was homogenous, non-enhancing, partially-calcified and encapsulated within an enlarged right SMG. Ultrasound-guided FNA biopsy was performed and demonstrated histologic features consistent with pleomorphic adenoma. However, given the rapid increase in the size of the right SMG, the patient underwent uneventful excisional biopsy of this mass. The final pathology report revealed a focus of carcinoma ex pleomorphic adenoma (CA ex-PA) with flow cytology showing no evidence of monoclonality. DISCUSION: This case report emphasizes the importance of long-term follow-up with close monitoring, regular clinical examinations and role of serial multiple imaging modalities. The early identification and timely appropriate treatment of presumed benign lesions that may undergo malignant transformation into CA ex-PA over time is paramount.