Anatomic Pathology / MUCOEPIDERMOID CARCINOMA INVOLVING WARTHIN TUMOR

We describe 5 cases of mucoepidermoid carcinoma (MEC) involving Warthin tumor (WT) of the parotid gland. The WT size ranged from 1.7 to 6.0 cm. The MECs were much smaller, 0.3 to 1.7 cm. In 3 cases, the WT completely surrounded the MEC, and in 2 cases neither WT nor MEC surrounded the other. Each MEC was low grade, 3 grade I and 2 grade II. One MEC had evidence of vascular invasion. All patients underwent partial or subtotal parotidectomy with negative resection margins. Clinical follow-up (range, 8-52 months) for 3 patients showed no evidence of recurrence. The pathogenetic relationship between WT and MEC in these cases is uncertain. In 4 cases, foci of squamous or mucous metaplasia were found in the WT component, associated with mild cytologic atypia in 3 tumors. However, a direct transition from WT to MEC was not identified. In 1 case, MEC was present 45 months before WT, suggesting that the recurrent MEC involved WT coincidentally. The small size and low grade of the MEC and the negative resection margins most likely explain the good outcome for the 3 patients with clinical follow-up data available. Warthin tumor (WT), also known as papillary cystadenoma lymphomatosum, is the second most common benign tumor of the parotid gland, representing 10.4% of all benign parotid gland tumors at the Armed Forces Institute of Pathology.1 Multicentricity and bilateral involvement, which may occur in synchronous or metachronous fashion, are more common in WT than in other salivary gland neoplasms.2-5 Histologically, WT is characterized by a variable mixture of lymphoid stroma and oncocytic epithelium, and the latter is often papillary.1-3 Carcinoma may arise rarely in WT. Nagao and colleagues6 reviewed the literature and identified 24 cases of carcinoma involving WT. In most instances, the carcinoma was thought to arise from WT. However, coincidental occurrence (so-called collision tumor) of WT and carcinoma is difficult to exclude. Squamous cell carcinoma is reported to be the most common type of carcinoma to arise within WT.7-9 Other types of carcinoma that have involved WT include oncocytic carcinoma,10 undifferentiated carcinoma,11 adenocarcinoma not otherwise classified,12 and mucoepidermoid carcinoma (MEC).6 To date, 5 cases of MEC arising within WT have been reported in the literature.6,13-15 In this article, we describe the clinical and pathologic features of 5 additional cases of MEC involving WT. Materials and Methods We searched the computerized files of the Department of Pathology of the University of Texas M.D. Anderson Cancer Center, Houston, for cases of WT and MEC from 1985 through December 1999. In the time period searched, 274 cases of WT were accessioned in our department, including 86 Anatomic Pathology / ORIGINAL ARTICLE Am J Clin Pathol 2000;114:564-570 565 © American Society of Clinical Pathologists consultation cases and 188 routinely signed out specimens. Five cases of WT with MEC of parotid gland were identified. Four cases were received in consultation, and 1 patient (case 5) underwent surgical excision at our institution. The number of slides available for review in each case ranged from 4 to 19 (median, 5 slides). Each WT was searched systematically for areas of lining cell hyperplasia, squamous and mucous metaplasia, and areas of transition from metaplastic WT epithelium to MEC. The MEC was assessed for its relationship with WT and evidence of invasion, and each MEC was graded histologically using a system reported by others.1 Clinical information was obtained from consultation letters, communication with referring pathologists, and review of available medical records.