Histopathological Pattern of Salivary Gland Tumors

Correspondence: Dr. Sadina Shrestha, MD Consultant Pathologist, Department of Pathology, B. P. Koirala Memorial Cancer Hospital, Bharatpur, Chitwan, Nepal Email: sadina_shrestha @yahoo.com Background: The tumors of the salivary glands are uncommon head and neck neoplasms. The aim of this study was to evaluate the relative frequencies, types, site distribution and the histopathological features of salivary gland tumors.


MATERIALS AND METHODS
The data for the present study was obtained from the medical record section and department of pathology from January 2005 to December 2010.Information regarding age, gender, tumor location and tumor size were determined for each salivary tumor type.The frequencies of different benign and malignant salivary tumors in both major and minor glands were identified.All the biopsy specimens were fixed in 10% formol-saline, then processed into paraffin embedded sections and stained with hematoxylin and eosin (H&E).The histopathology of all tumors was reviewed and classified according to the World Health Organization (WHO) histological typing of salivary gland tumors.

RESULTS
Out of 34,978 biopsies reported at B.P.Koirala Memorial Cancer Hospital during the study perioid, 176 cases were related to salivary gland tumor.Of the 176 cases, 66 (37.5% %) were benign and 110 (62.5 %) were malignant, representing a ratio of 1:1.6 respectively.Male were more affected by both benign and malignant tumors.The highest incidence for benign tumors was in the 3 rd and 4 th decade, where as for malignant tumor it was the 4 th and 5 th decade of life.The mean age observed for all salivary gland tumors was 44.76 years with age range of 12 to 75 years (Table 1).The most common site of occurrence for both benign and malignant tumors was parotid gland (Table 2).Distribution of benign salivary gland tumors are shown in Table 3.Of benign salivary gland tumors, pleomorphic adenoma (fig. 1) was the most common histologic type followed by warthin's tumor (fig.2).
Distribution of malignant tumors in salivary glands is shown in Table 4. Mucoepidermoid carcinoma (38.1%) was most common among the malignant salivary gland tumors.Parotid was the most common site of occurrence for mucoepidermoid carcinoma followed by minor salivary glands and submandibular gland.
Submandibular gland was the most common site of occurrence for adenoid cystic carcinoma (fig.4).Parotid was the third most common site of occurrence for acinic cell carcinoma (7.2 %) followed by submandibular gland (3.6 %).All cases of carcinoma ex pleomorphic adenoma, basal cell carcinoma, adenocarcinoma, squamous cell carcinoma, metastatic undifferentiated carcinoma involved only the parotid gland.
The commonest malignant tumor of parotid (23.6 %) and the minor salivary glands (9.0 %) was mucoepidermoid carcinoma.In the submandibular gland the most common malignant salivary gland tumor was adenoid cystic carcinoma (12.7 %).

DISCUSSION
In the present study of 176 cases of salivary gland tumors, 66 (37.5%) were benign and 110 (62.5%) were malignant.0][11] Since our study was based at cancer hospital where diagnosed malignant cases are referred for further management; it may have led to predominance of malignant ones.
In the present series mean age observed was 46.7 years with an age range of 12 to 75 years.Benign salivary gland tumors were more common in age group of 31 to 40 years and the peak age incidence observed for malignant salivary gland tumors was 41 to 50 years.Chatterjee et al. observed large number of benign cases in third decade followed by fourth decade. 12Malignancy reported in his study was predominant in the 5 th decade.
In the present study a male preponderance was noted with a male: female ratio of 1.7:1.This is in agreement with series reported by Potdar GG et al 13 Spiro et al 14 .However; this was in contrast to the series reported by Dandapat et al 15 and Rewsuwan et al 16 who reported a female preponderance in their series.][20] Similar findings were observed in the present study where pleomorphic adenoma was the most common benign salivary gland tumor at all locations.Out of total 48 pleomorphic adenomas in our study, majority occurred in the parotid gland (N=36; 54.5 %) followed by submandibular gland    (N=8; 12.1%) and minor salivary glands (N=4; 6.0%).Out of all reported cases of pleomorphic adenoma, 32 were males and 16 were females with a male to female ratio of 2:1.Potdar GG 13 reported 183 cases of pleomorphic adenomas, out of which 101 were involving parotid gland.Warthin tumor (14.29%) was the 2nd commonest benign tumors as quoted by Chung et al. 21Eight cases (12.1%) of Warthin tumor were involved in the parotid gland followed by (N=2; 3.0 %) of in submandibular gland which is similar to what has been reported by Eveson et al. 22 One case of lipoma was seen in our study.Literature review reveals that these are rare neoplasms of parotid, however occasional cases have been reported in the parotid gland. 23chwannoma presenting as primary salivary gland neoplasm is a recognized entity. 24These are thought to arise from the radicals of facial nerve.We observed two cases (3.0 %) of schwannoma, all affecting parotid gland.

Histopathological Pattern of Salivary Gland Tumors
Mucoepidermoid carcinoma was the most common malignant salivary gland tumor of parotid constituting 26 (23.6 %) of all malignant salivary gland tumors in the present series.Mucoepidermoid carcinoma was reported to be the most common malignant salivary gland tumor of parotid by Richardson et al 18 and Spiro et al. 14 In our study mucoepidermoid carcinoma was more common in parotid gland (N=26; 23.6 %) followed by minor salivary glands (N=10; 9.0 %) and submandibular gland (N=6; 5.4 %).
Richardson et al. 19 reported 61 cases of mucoepidermoid carcinoma and parotid (N=52) was reported to be the most common site of occurrence followed by minor salivary glands (N=6) and submandibular gland (N=3).
The most common malignant salivary gland tumor observed in submandibular salivary gland was adenoid cystic carcinoma accounting for (12.7 %) of all malignant salivary gland tumors.Similarly, Potdar et al 13 , Richardson et al 18 , and Rewsuwan et al 16 also found adenoid cystic carcinoma to be the most common malignant tumor of submandibular glands.Vergas et al 19 , reported five cases of adenoid cystic carcinoma in their series accounting for 4% of all cases or 20% of malignant tumors.It was also reported to be the second most common malignant salivary gland tumor in their series.In contrast to the present study, Lima et al 25 and Rewsuwan et al 16 reported adenoid cystic carcinoma to be the most common malignant salivary gland tumor in their series.
Carcinoma ex pleomorphic adenoma is an infrequent aggressive malignancy that is believed to evolve from a pre-existing benign adenoma.It accounts for 3.6% (range, 0.9%-14%) of all salivary neoplasms and for 11.7% (range, 2.8%-42.4%) of salivary malignancies. 26We found 6 cases (5.4 %) of carcinoma ex pleomorphic adenoma of the parotid gland.
Polymorphous low grade adenocarcinoma(PLA) occurs almost exclusively in minor salivary gland and its origin in a major salivary gland is considered rare.Although several report have described PLGA of the parotid gland. 27,28 e found two cases (3.0 %) of PLGA in parotid gland.
Primary squamous cell carcinoma of salivary gland is rare.Batsakis et al indicated that the true incidence to be 0.3% to 1.5%. 29We found only 4 (3.6 %) of squamous cell carcinoma in parotid gland in our series.

CONCLUSION
Salivary gland tumors are rare.Male and the parotid gland were the most affected and pleomorphic adenoma was the most frequent lesion, followed by mucoepidermoid carcinoma and adenoid cystic carcinoma.