Dedifferentiation in low-grade mucoepidermoid carcinoma of the parotid gland.

Division of Anatomic Pathology, Mayo Clinic, Rochester, MN 55905, USA.
Human Pathlogy (Impact Factor: 2.81). 11/2003; 34(10):1068-72. DOI: 10.1053/S0046-8177(03)00418-0
Source: PubMed

ABSTRACT Mucoepidermoid carcinoma (MEC), a common malignant salivary gland neoplasm, is generally divided into low-, intermediate-, and high-grade types according to the histologic features. To our knowledge, the present report describes the first case of dedifferentiation occurring in a low-grade MEC. A 55-year-old man presented with a biphasic neoplasm of the right parotid gland composed of low-grade MEC and dedifferentiated high-grade anaplastic undifferentiated carcinoma. Immunohistochemically, carcinoembryonic antigen expression was restricted to the low-grade MEC portion. The Ki-67-labeling index was higher in the dedifferentiated component than in the low-grade component. On image cytometric analysis, the low-grade MEC was diploid, whereas the dedifferentiated carcinoma was aneuploid. Although the patient was alive 10 years after the initial diagnosis, the tumor has recurred twice, at 3 months and 7 months after the initial resection. It is important to recognize that dedifferentiation can occur in a low-grade MEC, similar to other low-grade salivary gland carcinomas.

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    ABSTRACT: Summary. 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 highgrade 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.
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