A total of 278 hematoxylin and eosin stained archival slides from Tamil Nadu Government Dental College, Chennai which included cases of mild, moderate and severe epithelial dysplasia, carcinoma in situ, OSCC were histopathologically evaluated for the study after approval from the ethics committee. Of these, those with presence of salivary gland tissue were included in the study. The age, sex, site and histopathological diagnosis were collected from the records. The slides which exhibited ductal and glandular involvement were selected for the study. The total number of oral epithelial dysplasias and OSCC of different grades, verrucous carcinoma and carcinoma in situ were recorded. Oral epithelial dysplasia was graded as; mild, moderate and severe and OSCC was graded as well, moderately and poorly differentiated. The ductal changes in the salivary gland were recorded as ductal proliferation, metaplasia, dysplasia, inflammatory cell infiltration and malignant squamous infiltration. The acinar changes in the minor salivary glands were recorded as degeneration, squamous metaplasia, myoepithelial cell proliferation and inflammatory cell infiltration. The results were tabulated and statistical analysis was done using Statistical Package for the Social Sciences (SPSS) software v.17.0 (IBM, USA) for Windows 7 (Microsoft, USA).

Demographic data: The distribution of cases taken for the study has been shown in [Table/Fig-1]. Among the males, 6 (4%) showed lip involvement, 46 (31.7%) cases were in the buccal mucosa, 9(6.2%) in the palate, 16 (11%) in the tongue, 13 (6.9%) in the floor of mouth, 38 (26.2%) in the alveolus, 5 (3.4%) in the maxillary antrum and 12 (8.3%) cases in the retromolar area. In females 3 (2.3%) showed lip involvement, 70 (52.6%) were in the buccal mucosa, 5 (3.8%) in the palate, 8 (6%) in the tongue, 2 (15%) in the floor of mouth, 39 (29.3%) in the alveolus, 3 (2.3%) in the maxillary antrum and the retromolar area. [Table/Fig-2] shows the age distribution of oral epithelial dysplasias and OSCC in males and females. Maximum number of cases were observed in 51-60 years age group.

Ductal changes: The ductal changes observed in the excretory duct in various oral lesions have been listed in [Table/Fig-3]. The excretory duct seen in cases of OSCC showed eight cases of simple hyperplasia, six cases of squamous metaplasia and one case each of mucous and oncocytic metaplasia. Moderate dysplastic changes were seen in five cases and one case showed severe dysplasia. An inflammatory cell infiltrate was seen in 15 cases and seven cases showed infiltration by malignant cells into the duct. Ductal changes seen in the salivary gland were listed in [Table/Fig-4]. In OSCC we observed 15 cases of ductal proliferation and four cases of ductal metaplasia. Dysplastic changes of varying severity were observed in 13 cases which include nine cases of mild dysplasia and two cases each of moderate and severe dysplasia. Eighteen cases showed infiltration by malignant squamous cells.

Acinar changes: [Table/Fig-5] shows the acinar changes observed in our study. In our study 29 cases showed acinar degeneration [Table/Fig-6], 20 cases showed squamous metaplasia [Table/Fig-7] and eight cases showed myoepithelial cell proliferation. Out of these 30 cases one case showed only proliferation, 11 cases showed acinar degeneration of mild and moderate intensity and 18 cases showed both ductal and acinar degeneration [Table/Fig-8]. Inflammatory cell reaction varied from mild inflammation in 11 cases, moderate inflammation in 16 cases and severe inflammation in three cases. [Table/Fig-9,10] shows dysplastic salivary gland cells in the connective tissue, dysplastic changes in epithelium, excretory duct and gland.

[Table/Fig-6]:

Photomicrograph of salivary gland showing acinar degeneration (H&E stain X40).

[Table/Fig-7]:

Photomicrograph of salivary gland showing squamous metaplasia (H&E stain X100).

[Table/Fig-9]:

Photomicrograph showing streaming of dysplastic salivary gland cells in the connective tissue (H&E stain X100).

[Table/Fig-10]:

Photomicrograph showing dysplastic changes in epithelium, excretory duct and gland (H&E stain X40).

One of the important causes for OSCC is tobacco and tobacco related products. Recently areca nut has also been proposed as an etiological factor for OSCC [3–5]. Although the etiology for Potentially Malignant Disorders (PMD) has been well defined, the cause for salivary gland carcinomas has not been that clear. Viruses such as Epstein Barr Virus (EBV) have been associated with malignant tumours of the salivary glands [6]. Association of ionizing radiation and risk of salivary gland tumours has been described by few authors [7,8]. Another important etiological factor associated with salivary gland cancers is occupation related. Exposure to metals in the plumbing and rubber industry, nickel compounds, woodworkers and personnel in the automobile industry are some of the occupations associated with increased risk of salivary gland cancers. Other occupations include personnel involved in asbestos mining and those in beauty shops and hairdressing [9ဓ12]. However the effect of epithelial dysplasia and OSCC on the minor salivary gland is not well documented. Hence, this study was undertaken to investigate the salivary glandular changes in reported cases of oral epithelial dysplasia and OSCC.

In this study the most common site where oral epithelial dysplasia and OSCC occurred were in the buccal mucosa and 50-60 years age group was most commonly affected as observed in other studies [13–15]. This is due to the tobacco chewing habit of the patients of both the sexes.

The different changes observed in the minor salivary glands along with ducts were carefully assessed. In the excretory duct following changes were observed which include; simple hyperplasia, mucous, oncocytic and squamous metaplasia and dysplasia. Simple hyperplasia is the increase in the thickness of same type of cells in the duct. The simple hyperplasia and metaplasia are adaptive changes that occur in the excretory duct possibly due to the effect of chemical carcinogens or due to OSCC [16,17]. Although these changes are reversible, their occurrence is highly undesirable and persistence of this adverse environment may predispose such tissues to dysplastic changes and a fertile area for malignant transformation. The presence of varying degrees of dysplasia was also observed in our study among cases of epithelial dysplasia, OSCC and verrucous carcinoma which is similar to the study by Browne RM and Potts AJC [18]. This dysplasia may be due to accumulation of the potential carcinogens over a length of time and it has been postulated that the degree of dysplasia in a duct increased with the increasing severity in the epithelium [19].

The glandular changes observed in our study were proliferation and degeneration of the salivary acini. These changes have been observed possibly due to several reasons. The chemical carcinogens might have caused ischemia which in turn might have induced proliferation and degeneration of salivary gland acini [20,21].

We observed squamous metaplasia of the acini in 20 out of 32 cases. Similar to ductal metaplasia, squamous changes in the acini can also be as a result of OSCC or irritation by chemical carcinogens and ischemia. It has been observed in experimental conditions that the squamous metaplasia can turn into squamous cell carcinoma via a non-genotoxic, proliferation-dependent mechanism [22]. It should also be noted that the acinar intercalated duct complex plays a very important role in development of salivary gland tumours. We also observed that 25% of our sections showed a myoepithelial cell proliferation (neoplastic myoepithelial cells) which is a very important constituent in the development of malignant tumours in the salivary glands [23–25]. About 90.6% of our cases showed presence of inflammatory cells in the salivary gland of varying intensities. The presence of inflammatory cells is indicative of immunological defense reaction of the host in contrast to metaplastic or dysplastic changes which favours malignant transformation [26].

In our study one case of severe dysplasia and a case of squamous cell carcinoma showed changes both in the surface epithelium and the salivary gland. The excretory duct of the oral dysplastic lesion showed ductal dysplasia within the glandular zone. The dysplastic glandular cells showed a streaming effect [Table/Fig-9]. This histological appearance suggests the possible histogenesis of adenosquamous carcinoma, the squamous cell carcinoma arising from the surface epithelium and adenocarcinoma arising from the excretory ductal and salivary glandular dysplastic epithelial cells. The simultaneous malignant changes in these two different types of epithelium were observed in our study [Table/Fig-10]. The probable origin is the surface epithelium with changes seen in the salivary gland [27,28].

It is very important to assess the changes in the minor salivary glands in cases of oral epithelial dysplasia and OSCC. Removal of salivary gland tissue is essential which may act as a potential source for recurrence of oral epithelial dysplasia and OSCC. Care should be taken to remove appropriate amount of tissue while excising pre-malignant and malignant lesions. The excised tissue should bear the minor salivary glands which have undergone changes during the process of dysplasia. There have been reports of recurrence of OSCC due to inadequate removal of salivary gland tissue and hence it is very important to remove the salivary tissue while excising oral epithelial dysplasias or OSCC [29–31].

Though this is a preliminary study, further studies to evaluate why the changes occur in minor salivary glands is important.

The present study revealed interesting histopathological changes of salivary glandular tissue in cases of oral epithelial dysplasia and OSCC. In view of these observations it is suggested that histopathological interpretation for oral mucosal lesions especially oral epithelial dysplasia and OSCC also includes changes related to salivary gland tissue.