| Abstract|| |
Warthin's tumor also known as papillary cystadenoma lymphomatosum is a common benign salivary gland neoplasm that occurs exclusively in parotid gland. Rarely, the tumor can undergo carcinomatous or lymphomatous transformation of epithelial or lymphoid component, respectively. Herein, we describe a case of 55-year-old female who had undergone parotidectomy for a rapidly growing tumor in the right parotid gland. The case was diagnosed as mucoepidermoid carcinoma developed in a setting of Warthin's tumor based on the histomorphology, special staining characters, and immunohistochemical findings. The pathogenesis and differential diagnoses of such rare malignancy has been discussed briefly.
Keywords: Mucoepidermoid carcinoma, salivary gland, Warthin′s tumor
|How to cite this article:|
Mohapatra M, Satyanarayana S. Low grade mucoepidermoid carcinoma in a setting of Warthin's tumor. Indian J Pathol Microbiol 2012;55:392-4
| Introduction|| |
Warthin's tumor is a benign salivary gland neoplasm composed of cystic structures lined by bilayered oncocytic and basaloid epithelium sharply delineated from underlying lymphoid stroma. Usually occurs in males in 6th-7th decade.  The tumor accounts for 10% of all salivary gland tumors.  Both epithelial and lymphoid component of the tumor can undergo malignant transformation. However, malignant transformation of epithelial component is extremely rare, seen in only 0.3% cases.  There are only few reports in the world literature depicting the epithelial malignancy arising in Warthin's tumor. Herein, we describe a case suspected to be mucoepidermoid carcinoma developed in a background of Warthin's tumor by light microscopy which was further confirmed by special staining and immunohistochemistry.
| Case Report|| |
A 55-year-old female had a right parotid swelling for 2 years duration, with history of rapid growth. She had undergone superficial parotidectomy elsewhere. Hematoxylin and eosin stained slides and paraffin blocks were received for review. Microsections showed a cystic tumor with stratified epithelial lining thrown into papillary projections. The lining epithelium comprised of luminal tall columnar oncocytic cells, mucin secreting goblet cells along with squamous cells and discontinuously present abluminal basaloid cells. The stroma underneath the cyst showed dense lymphocytic infiltrate forming lymphoid follicles with germinal center at places [Figure 1]a and b. There were areas of mucin pools, mucinous glands and squamoid cell nests invading into the stroma [Figure 1]c and d. Meticulous searching revealed focal area in the tumor showing a transition zone from columnar oncocytic cells to hyperplastic mucin secreting goblet cell and squamous cells [Figure 2]a. The presence of mucin in columnar goblet cells was further confirmed by positive periodic acid-Schiff (PAS) reaction [Figure 2]b. The oncocytic cells were PAS negative.
|Figure 1: (a) Cystic tumor with papillary structures (H and E, ×100). (b) Papillae lined by oncocytic cells, mucin secreting cells, squamoid cells (H and E, ×400), and dense lymphoid stroma with germinal center (Inset). (c) Lining epithelium showing hyperplastic squamoid cells (H and E, ×400). (d) Invasive island of squamous cells (H and E, ×400)|
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|Figure 2: (a) Transition zone in the lining epithelium showing oncocytic cells to columnar mucin secreting cells (H and E, ×400). (b) PAS positive columnar mucinous cells (H and E, ×400). (c) SMA negative tumor cells lining the cyst [SMA] (×100). (d) CK positive basaloid cells under the oncocytic cells, mucinous, and squamoid cells in transition zone [CK] (×100)|
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Considering the clinical and microscopic picture, the case was offered two diagnoses: (i) Low grade mucoepidermoid carcinoma developed in a setting of Warthin's tumor and (ii) Mucoepidermoid carcinoma with lymphoid rich stroma.
The tumor was negative for smooth muscle antigen (SMA) which excluded the presence of myoepithelial cell [Figure 2]c. Cytokeratin (CK) was positive in basaloid cells underneath the oncocytic cells, mucin secreting cells, and squamous cells in the transition zone and also in lining cells of invasive mucinous glands as well as squamous islands but negative in oncocytic cells [Figure 2]d. Thus, based on the histopathologic and immunohistochemical findings, the case was confirmed to be low grade mucoepidermoid carcinoma developed in a setting of Warthin's tumor.
| Discussion|| |
Warthin's tumor is the second most common benign salivary gland neoplasm mostly occurring in parotid or periparotid region. In the parotid gland, the tumor usually arises from the tail or deep lobe. Morphogenesis of the tumor is thought to be from heterotopic salivary duct entrapped in parotid or periparotid lymphoid tissue. Warthin's tumor can undergo malignant transformation of epithelial or lymphoid component. Malignant transformation rarely may occur spontaneously or following radiotherapy. Epithelial malignancy in Warthin's tumor can be of squamous cell carcinoma, oncocytic carcinoma, adenocarcinomas, poorly differentiated carcinoma, and mucoepidermoid carcinoma. ,,,,,,
Mucoepidermoid carcinoma is a relatively uncommon tumor normally arising from major and minor salivary glands and tracheo-bronchial tree. Sometimes in mucoepidermoid carcinoma, the spillage of cyst content into the stroma evokes dense lymphocytic infiltration which can be exuberant to form lymphoid follicle. But, this infiltrate is usually focal.  In our case, the presence of dense lymphocytic aggregate was observed in all the areas, which excluded this possibility.
Epithelial neoplasia in Warthin's tumor can occur in three forms, ,
Since, primary carcinoma arising in warthin's tumor is least commonly encountered, it is essential to exclude the possibility of metastasis from primary carcinomas in head and neck region. In our case, there was no such primary. Histomorphologically, the tumor resembled Warthin's tumor with areas of mucoepidermoid carcinoma along with focal area showing a transition zone from columnar oncocytic epithelium to hyperplastic-dysplastic mucinous and squamous epithelium. It has been documented that the malignant transformation in pre-existing Warthin's tumor is to be considered only when the bulk of the carcinoma is inside the Warthin's tumor and the oncocytic epithelium shows a transition zone from hyperplastic-dysplastic state to malignancy.  The pathogenesis of primary epithelial malignancy developing over Warthin's tumor is enigmatic. Squamous or goblet cell metaplasia of oncocytic cells is thought to have a role. Epithelial component can show metaplastic change in response to inflammation or infarction. Yamada et al. has ascribed that neoplastic cells of Warthin's tumor, i.e., the oncocytic cells acquire malignant phenotype simultaneously with such metaplastic change. Though, oncocytic cells can be verified by positive reaction with phosphotungstic acid hematoxylin stain or electron microscopy, it was not done in our case. However, we confirmed the presence of mucin in columnar mucinous cells by PAS stain which yielded negative reaction in columnar oncocytic cells.
- A coexistent separate neoplasm (most common). Warthin's tumor is frequently associated with a second tumor, which may arise synchronously or metachronously from same or opposite side; pleomorphic adenoma being the commonest.
- Metastatic deposit in lymphoid stroma from primary carcinoma in head and neck region.
- Primary carcinoma arising in epithelial component (least common).
The possibility of commonly observed coexistent second neoplasm, i.e., pleomorphic adenoma was excluded by immunhistochemical marker study with SMA which was negative, excluding the presence of myoepthelial cells. CK positivity in the basaloid cells beneath the oncocytic cells, squamoid cells, and mucinous cells lining the cyst as well as the glands invading in to the lymphoid stroma not only verified the transition zone from benign oncocytic to metaplastic epithelium but also ascertained the mucoepidermoid carcinomatous tissue.
Hence, while diagnosing Warthin's tumor of long standing duration with history of rapid growth, the rare occurrence of malignant transformation should be considered. Such cases can be evaluated accurately with the help of special stains and immunohistochemistry.
| Acknowledgment|| |
The authors are thankful to Prof. C. Sundaram and Prof. A. Prayaga of Pathology Department, NIMS, Hyderabad for their help and cooperation.
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Department of Pathology, G S L Medical College and General Hospital, NH-5, Lakshmipuram, Rajahmundry - 533 294, Andhra Pradesh
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]