Clinico-epidemiological profile of salivary gland tumours: An institutional study

Introduction

Salivary gland tumors (SGT) are rare, constituting 5% of all head and neck cancers and 0.5% of total body malignancies, with an annual incidence of 0.5–2 patients/100,000 people.1, 2, 3, 4 Most occur in the sixth decade of life. The proportional morbidity for men and women is similar with ratio of 1.3: 1. The SGT develops in large (parotid, sub- -mandibular sublingual) as well as in small salivary glands located within the mucous membrane of the upper section of the gastrointestinal tract.3 The majority occur in the parotid gland (70%) and they are less common in minor salivary (20%), submandibular (10%), and sublingual (7%). SGT are a very non-homogenous group, in which 32 histological types and subtypes can be distinguished.5

Therefore, the epidemiology of these neoplasms is not well recognized. Many studies include only data on parotid gland cancer, others contain data concerning only the large salivary glands.6 As a relatively large number of neoplasms are benign lesions, epidemiological data are incomplete and can in many cases be underestimated. Additionally, because of the rarity of incidence and great diversity of those neoplasms, data concerning the etiology of specific histopathological types are scant.7 In this paper, we present the latest epidemiological data concerning SGT in our region. With regards to malignant SGTs, the smaller the salivary gland the higher the risk of malignancy, with nearly 100% of sublingual and 60% of minor salivary gland tumours diagnosed as malignant.8

To date, most of the epidemiological studies on SGTs are limited for a variety of reason including being out of date, extrapolated from either a single centre or country studies, or investigating either major or minor glands only.

Materials and Methods

The retrospective study was consisted of 245 cases of major and minor SGT selected among 32,789 cases over the 5yr recorded in the files of the Laboratory of clinically and histopathological diagnosed cases of SGTs from tertiary regional cancer centre, government medical college and government dental college.

Data collection was based on information obtained with the sample’s results of histopathology exams, which were reproduced to a usual file developed specifically for this analysis. Patents’ age, gender as well as anatomical site and histopathological diagnosis of lesion were the explored variables. Among the histopathological results obtained in the files, all cases were revised and reclassified based on 5^th edition of World Health Organization classification (2022) on the basis of neoplastic and non-neoplastic lesion.

Results

All 243 cases of SGT corresponded to 0.15% of the total cases registered by this laboratory during the stated period. Malignant neoplasm were more common than benign ones, while Mucoepidermoid carcinoma was the most frequent type (Table 7). Regarding malignant neoplasm, mucoepidermoid carcinoma followed by adenoid cystic carcinoma and Adenocarcinoma were the most frequently observed types (Table 7). The majority (61%) of the SGT presented in minor and 39% in the major salivary glands. Considering the anatomical site, greater salivary glands, especially the palate followed by involving site was parotid gland, submandibular gland and sublingual gland respectively (Table 6), were the most affected both by benign and malignant neoplasias.

Concerning patients’ gender, women were more frequently affected (Table 4). Peak incidence relative to age was the fifth and sixth decades for benign and malignant neoplasias (Table 5), respectively.

Discussion

Salivary glands are divided into major and minor ones. Major salivary glands include parotid, submandibular, and sublingual glands and minor ones include hundreds of small glands scattered throughout the oropharynx, nose, sinuses, larynx, and trachea. 7 Both benign and malignant lesions may be seen in salivary glands. Chance of being benign or malignant varies in different sites. 3 Epidemiological studies of epithelial SGT are difficult to conduct effectively due to tumor rarity, histological heterogeneity, tumor location diversity and a lack of national registries collecting data, especially for benign tumors. 8, 9

Alteration in salivary glandular epithelium may produce such diversities in histopathological expressions that the development of a universal classification accepted by researchers is very hard, especially when diagnosing certain neoplasia’s. Multiple histological aspects of SGT have been attributed to presence of myoepithelial cells in these glands. There were several attempts to classify these lesions in the past years, and the most recent and adopted classification is the World Health Organization publication (2022). 1, 2 It is clear that this document aims at grouping all known SGT into two major groups: benign and malignant. Once this classification was developed by an institution accepted and recognized worldwide, the present study followed their criteria. 10

Out of 353 cases of major and minor epithelial salivary glandular lesion, it was observed that minor salivary glands were most commonly affected in both non neoplastic lesion and neoplastic lesion i.e. both in benign and malignant tumors, specifically the palate (61.6%). Tumours involving minor glands have worse prognosis, higher recurrence rate and poor outcomes compared to major gland tumours.

In the present study, parotid gland represented the second most frequent site of benign and malignant tumors, which was favoured with Rivera-Bastidas H et al. few cases were recognised in submandibular and sublingual salivary gland respectively.5 Benign SGT were more frequent in female than in male at a 3:1 rate, with mean age of 46.1 years. Malignant neoplasias were also observed with higher frequency in female at a 2:1 ration and mean age of 64.8 years. Similar findings were studied in Solange Souza Lima et al. 11

Peak incidence of benign SGT was experiential at the fourth decade of life and malignant SGT was fifth decade of individuals. Some literature showed that for benign SGT, and malignant SGT was observed fifth decade and seventh decade respectively, partly substantiating the findings with the present study, except for benign SGT. 8, 12, 13

On basis of histopathological diagnosis in this study, pleomorphic adenoma was the most frequent lesion (41.96%) among benign SGT, which is in accordance with most literature around the world. Out of 47 cases of pleomorphic adenoma, 34 (72.34%) occurred in female, with a peak incidence at the fourth decade of life and mean age of 39.2 years. The most frequent site of pleomorphic adenomas in this study was the minor salivary gland i.e. palate; however, it is important to emphasize that this neoplasia was also the most frequently found in other salivary glands, which is accordance with other authors reported in their study. 1, 5

Malignant tumors of salivary glands summed 131 cases (53.90%), among which mucoepidermoid carcinoma was the majority, totalizing 54 cases (41.22%). These findings are similar with the Otoh EC et al and Stryjewska-Makuch G et al. 6, 7 although Solange Souza Lima et al are reporting the Adenoid cystic carcinoma is the most frequent malignant SGT. 11, 14

Increasing numbers of researchers are highlighting the importance of genetic alterations as biomarkers of salivary gland pathology. It has been suggested that the genetic changes have also prognostic and predictive potential. 1 Alterations at the genetic level result in changes to the tumour microenvironment. In summary, the data presented in this study are very similar to those of other published research studies. We concluded that the incidence of salivary gland neoplasia in the Marathwada region is in accordance with the incidence observed in several other regions of worldwide.15

Conclusion

Correct diagnosis of salivary gland lesion is essential in determining the treatment and prognosis of the patient. SGT are a diverse group of disease and each patient must be treated individually. The data demonstrated that epidemiology profile of the studied neoplasms corroborated most of the studied literature.

In the future, the importance of genetic alterations in the diagnosis of salivary gland pathology will increase even more. These alterations will also be helpful as prognostic and predictive biomarkers, and may also serve as targets for anti-cancer therapies.

Source of Funding

None.

Conflict of Interest

None.