Mucoepidermoid carcinoma ex pleomorphic adenoma: A rare diagnostically challenging entity.

Mucoepidermoid carcinoma (MEC) arising in pleomorphic adenoma (PA) is an extremely rare entity. Involvement of minor salivary glands by this entity has only being described twice previously. We report on a diagnostically challenging case in an 18 year old male with a large mass in the junction of the hard and soft palates that has been present for 12 months. Both cytology and incisional biopsy were inconclusive and indicated benign mixed tumour. Upon excision of the tumour with a 5 mm clear margin, histology demonstrated PA that has been replaced by small nests and cribriform islands of high-grade MEC with 13 mm of invasion beyond the original PA capsule. The tumour was composed of mostly intermediate-type cells with up to 7 mitoses per 10 high power fields. The tumour cells were positive for cytokeratin (CAM 5.2) and S100. Due to the high-grade nature and focal positive posterior margin of the resected specimen, adjuvant radiotherapy was administered. In conclusion, this case highlights the need to consider rare entities such as mucoepidermoid carcinoma ex pleomorphic adenoma in atypical cytological and histological findings. Moreover, it underlines the need to manage lesions with unconfirmed histological diagnosis with wide excision margins to avoid having involved margins post resection.