High-grade epithelial carcinoma arising in a low-grade epithelial myoepithelial carcinoma of the parotid gland: a rare case report with immunohistochemical and molecular analysis

A case of high-grade epithelial carcinoma arising in a low-grade epithelial-myoepithelial carcinoma of the parotid gland is described. The patient was a 52 year-old male who presented a parotideal lump of approximately 20 mm in diameter and underwent excisional surgery. Histologically a typical low-grade epithelial myoepithelial carcinoma was evidenced and, in its context, an area of 7 x 4 mm showing focal aspects of a high-grade adenocarcinoma. The immunohistochemical pattern of the ductal epithelial cells of the low-grade component was similar to that of the epithelial cells of the high-grade carcinoma. The Ki-67 labelling index of the epithelial-myoepithelial carcinoma was 5%, whereas that of the high-grade lesion was 30%. EGFR, p53 and HER-2 genes seem to play no role in the biological behaviour of the tumour, as well as p16CDKN2A, BRAF, NRAS and C-KIT genes studied with biomolecular methods in both the high-grade and low-grade components. No local recurrence occurred after surgery, but multiple bone, cutaneous and lung metastases were detected 10 months later. The patient died 19 months after diagnosis.