Myoepithelioma of the Submandibular Gland Occurring after Cardiac Transplantation

Abstract

Myoepithelioma is a tumor composed entirely or almost exclusively of myoepithelial cells. It is an uncommon neoplasm, accounting for less than 1% of all salivary gland tumors. Immunosuppressed recipients of human donor organ grafts have an increased incidence of neoplasia.1 This represents an effect of long-term immunosuppressive therapy. In the present report we present a case of myoepithelioma of the submandibular gland occurring in a cardiac-transplanted man. To the best of our knowledge no case of such an association has been reported.A 61-year-old man underwent a heart transplantation in March 1992. He required it for the treatment of severe left ventricular failure after cardiac valve surgery. The patient has been treated since 1992 with an immunosuppressive regimen consisting of a combination of CSA, prednisone and aziathoprine. On June 1995, he was admitted to the hospital for excision of an asymptomatic mass in the right submandibular gland. The mass had been present for 14 months after heart transplantation. Physical examination revealed a firm, non-tender, nonfluctuant and freely movable mass. Excision of the gland was performed.Gross examination of the submandibular gland showed at the transection a well-circumscribed nodule, 13 cm in diameter, embedded in the gland. The tumor was whitish, firm and it showed a paracentral cyst filled with mucoid fluid. The remains of the gland were normal. Microscopically, a well-delineated tumor mass was separated from the surrounding salival gland by a thick hyalinized connective tissue capsule. The neoplasm was solidly packed with uniform epithelial cells and a scant, hyalinized stroma ( Figure 1). The tumor cells were spindle-shaped, with centrally placed nuclei containing delicately dispersed chromatin and a thin nuclear envelope. The nuclei occupied most of the cell bodies. The cells were bipolar, with slightly eosinophilic cytoplasm which varied from granular to fibrillar. The stroma was characterized by the presence of an amount of amorphous and acellular material in which a few fibroblasts and small collagen fibers were scattered. The tumor contained a few small isolated intercalated ducts; they were lined with a single layer of small cells with round and dense nuclei. The number of ductal structures was 0.4 in every 220x magnification field. The central cyst was lined by a single layer of flattened ductal epithelium. The neoplastic cells were diffusely positive for anti-human alpha-smooth muscle actin, anti-vitamin, and anti-S-100 protein, and were negative for anti-keratin cocktail CK22. The DNA histogram showed a diploid pattern, GO-GI, S and G2+M phase fractions were 94.5%, 3.4% and 2.1% respectively. Coefficient of variation was 8.9%. With all these findings, the pathological diagnosis was spindle-cell myoepithelioma.The incidence of the novo neoplasms in patients who have received solid organ transplants is of 3% to 11% within the first year and up to 21% after five years.2 Lanza et al. 3 reported a 10% incidence of malignant neoplasms in 53 patients w...