Mucoepidermoid carcinoma of the parotid gland showing oncocytic differentiation: three cases in the elderly mimicking benign lesions and diagnostic challenges

Öztürk Ç., Okcu O.

38th European Congress of Pathology, Stockholm, İsveç, 12 - 16 Eylül 2026, cilt.489, ss.735-736, (Özet Bildiri)

  • Yayın Türü: Bildiri / Özet Bildiri
  • Cilt numarası: 489
  • Basıldığı Şehir: Stockholm
  • Basıldığı Ülke: İsveç
  • Sayfa Sayıları: ss.735-736
  • Recep Tayyip Erdoğan Üniversitesi Adresli: Evet

Özet

Background & Objectives: Mucoepidermoid carcinoma (MEC) is a common malignancy of the salivary glands; however, its oncocytic variant is a rare diagnostic enigma. Consisting almost entirely of eosinophilic, granular oncocytes, these tumours can resemble benign conditions, such as Warthin tumours or oncocytomas. This diagnostic challenge is particularly acute in elderly patients, in whom benign oncocytic lesions are most prevalent. In this report, we present three cases of parotid-located oncocytic MEC. These cases are in patients aged between 60 and 80. We also highlight potential diagnostic pitfalls. Methods: Case 1: A 63-year-old male presented with a 3.8 cm solid parotid mass. While initial cytology suggested malignancy, histopathology confirmed intermediate-grade oncocytic MEC. No lymph node metastasis was detected. Case 2: A 71-year-old female presented with a 2 cm cystic lesion. Post-parotidectomy, the diagnosis was low-grade oncocytic MEC. Case 3: A 76-year-old male presented with a 4.2 cm cystic swelling. Histopathological evaluation confirmed a lowgrade oncocytic MEC variant. Results: Tumour samples from patients revealed abundant, granular, and eosinophilic cytoplasmic oncocytic cells, and within this predominant oncocytic background, mucous (mucin-producing) and intermediate cells, which are classic components of MEC. Conclusion: Oncocytic mucoepidermoid carcinomas (MECs) often appear similar to benign conditions during clinical and radiological examinations. Solid forms, as seen in Case 1, can be mistaken for oncocytomas, whereas cystic forms, as observed in Cases 2 and 3, usually resemble Warthin tumours. These similarities can result in a misdiagnosis prior to surgery, particularly in elderly patients. To avoid this, it is vital that pathologists examine highmagnification slides carefully for subtle indicators such as intracellular mucin (goblet-like cells) and small squamoid areas. Mucin stains, such as Mucicarmen or PAS-D, are often required for this purpose. If oncocytic proliferation is detected in a parotid mass in an elderly patient, the malignant oncocytic MEC variant must be included in the differential diagnosis to ensure appropriate surgical treatment is provided and a cancer diagnosis is not overlooked.