Tumor seeding to the submandibular gland can take place via three courses: hematogenous, lymphatic and direct extension (1). Around 66–100% of metastasis occurs by direct invasion by the primary tumor which ranges between 0.6 and 3% (17). Spread through metastatic cervical lymph nodes constitutes 0-1.5% of cases in the literature (17). Metastasis to level 1b lymph nodes in patients presenting with OSCC is considered frequent, however, submandibular gland invasion is rare (17).
Metastasis by hematogenous route occurs more frequently from primaries that do not originate from the head and neck region, which includes breast, genitourinary system and lung (1, 7).
Head and neck tumors majorly spread to the parotid gland while tumors originating below the clavicles metastasize to submandibular gland (breast, kidney, and lung) (18). The fibrous capsule enclosing the submandibular gland offers effectual impediment to the spread of cancer in previously untreated patients. The spread to the glandular parenchyma is seldom observed even though the gland may be compressed by massive metastatic disease (19).
The decision for submandibular gland resection must be made during the surgical procedure on the basis of inspection and frozen Sect. (17). However, the reliable modality for detection of metastasis to submandibular gland is ultrasonography (18).
Preservation of submandibular gland offers multiple potential benefits (20). Hyposalivation which increases the risk of oral infections can be avoided in patients who do not undergo radiotherapy (20, 21). This results in undiminished basal salivary flow that is primarily mucinous, and is responsible for the sensation of mucosal lubrication (20). Furthermore, basal salivary flow is vital for maintaining good oral hygiene (22). Secondly, submandibular glands are more responsive to therapeutic agents at minimizing xerostomia both during and after radiation therapy (23). A number of therapies for xerostomia include medications, acupuncture, synthetic saliva, gustatory stimulus, electrostimulation and autologous saliva storage. Some of these therapies have side effects and none of them have proved to improve patient’s quality of life (10, 24).
Finally, preserving the gland maintains the external contour of the superior neck region, along with lowering the risk of injury to the lingual and hypoglossal nerves (25).
According to our study, out of 90 patients, 5 patients were positive for submandibular gland involvement. Tumor related variables primary site and depth of invasion were found to have statistically significant association with submandibular gland involvement. Participants presenting with OSCC of buccal mucosa (2/57), mandible (1/11) and floor of the mouth (2/3) demonstrated submandibular gland involvement by tumor cells. This coincides with the results of a study which showed submandibular gland invasion in similar sites including buccal mucosa (5/35), floor of the mouth (5/13)and tongue (11/178) (26). Another study that was conducted to evaluate the oncological safety to leave the ipsilateral submandibular gland also supports the results of this study in terms of primary site involvement, demonstrating submandibular gland involvement in just one patient out of 107 with buccal mucosa being the primary tumor site (1).
According to a study which evaluated the submandibular gland metastasis in the head and neck cancer, excision of submandibular gland should be done in patients presenting with head and neck cancer and in patients with level I nodes invasion (16). In the current study, level Ib nodes were positive in 26 patients. However, submandibular gland involvement was observed in only 4 patients. Statistically significant association was also observed between positive level Ib and submandibular gland involvement. This is supported by results of another study which demonstrated only four patients with extra nodal extension to level Ib lymph nodes and had submandibular gland involvement which makes it look like involvement of submandibular gland takes place by direct spread with extra nodal extension and not via lymphatics (27). A retrospective study evaluated 229 salivary glands and found malignancy in only 3 patients (3). All these cases were positive for level Ib involvement (3).
As a part of our study depth of invasion was recorded. It ranged from 0.2 cm to 5 cm with 0.95 cm being the median value. This was compared to median value (10.0 cm) reported in another study which was closer to the median reported in our study (27). Statistical test was applied to test the association between submandibular gland involvement and depth of invasion. A highly significant association was observed between the two variables (p = 0.02).
Around 50% of the participants presented with stage IV tumor. Submandibular gland involvement was observed in all the patients. 2 participants with stage III tumor and 3 participants with stage IV tumor demonstrated submandibular gland involvement. However, a non- significant association was observed between tumor stage and submandibular gland involvement.