Salivary glands are exocrine glands that produce saliva in the oral cavity. The major salivary glands are parotid, submandibular, and sublingual. The minor salivary glands line the oral mucosa and the upper digestive tract. Salivary gland tumors are uncommon. The most common tumor site is the Parotid gland. When a tumor occurs in the Parotid, it is most likely benign, as it is the least likely site for the tumor to develop into a malignancy. [1]
Figure 1. Major salivary glands [2]
How common is it?
Malignancies of the salivary glands are rare and have unknown etiology. Interestingly, salivary gland cancer is on the rise in the US. [3, 4] Associated risk factors are a history of previous cancer, a history of long-standing benign tumors in the salivary gland, and a history of irradiation of the gland. Malignancies have a higher prevalence in older patients and are more likely to occur in male patients.
The relative five-year survival rate for adults diagnosed with salivary gland malignancy is estimated to be 65%. The survival rate decreases with an increase in age in male patients and changes with tumor site. [4]
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In a critical review paper by Guzzo et al., it was stated that the likelihood of a tumor growth presenting as a malignancy is site-dependent. Malignancies in the major salivary glands make up 15-32% of parotid tumors, 41–45% of submandibular tumors, and 70–90% of sublingual tumors. Malignancies involving the minor salivary glands are site-specific as well. In the palate, the rate is 40–60%. The tongue, the floor of the mouth, and sublingual glands have a higher incidence of malignant tumors, estimated at 90%. [1]
Clinical Presentation
Benign salivary tumors are usually slow, painless, and growing swelling not associated with infection or inflammation. [1] Malignant salivary gland tumors are rapid swellings not associated with infection or inflammation. Malignancy of the parotid may result in facial nerve involvement presenting as pain, paresthesia, or progressive loss of nerve function. [5] Cervical adenopathy is a sign of an advanced stage of malignancy. [1]
How to diagnose it and treatment options
Extraoral examination, intraoral examination (Figure 1), and thorough history taking of the present condition are essential to initial diagnosis. Assessment of cranial nerves in the growth region will aid in assessing possible malignancy. Ultrasounds can differentiate between intraglandular and extra-glandular lesions at the superficial layer. CT or MRI may be helpful in more extensive tumors. [6][5][1] If imaging is suggestive of a malignant tumor, then a biopsy is mandated to confirm the diagnosis before destructive surgery to remove the tumor. Fine needle aspiration cytology is used to biopsy salivary gland tumors to confirm malignancy without any tissue removal and surgical destruction. [1]
Surgical excision of the Salivary gland tumor is the standard treatment option for operable major and minor salivary glands. Post-surgical radiotherapy is recommended if residual cancer cells are left behind. Chemotherapy is usually used as a palliative means for non-operable advanced salivary gland malignancies. [1][5]
Figure 2. Structures within the oral cavity that require assessment during an intraoral examination.
Prognosis of Salivary Gland Tumors
Salivary gland tumors are classified according to the WHO histological classification published in 2005. These tumors are graded as high, intermediate, or low. The prognosis of salivary gland tumors (figure 3) is associated with tumor stage, histology classification, and grading. Other factors contributing to a less favorable prognosis are signs of nerve infiltration, extra tumor extension and cervical node involvement, patient’s age, and tumor site presentation. The most common Malignant epithelial tumors are Mucoepidermoid carcinoma, Adenoid cystic carcinoma, and Acinic cell Carcinoma. [1] [5]
Conclusion
Figure 3.
Patients who have received surgical resection of salivary gland tissue will experience reduced salivary flow and possibly limitation of oral mucosal or jaw movements. Post-salivary cancer treatment patients should be scheduled for frequent follow-up appointments. Patient education is critical to ensuring regular maintenance. It is essential to assess the local recurrence of the tumor and the effects of salivary gland hypofunction and tooth decay, identify potential sources of infection, and treat conservatively early. Fluoride application and optimum hygiene are essential in minimizing xerostomia-induced tooth decay. [7]
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References
- Guzzo, M., Locati, L. D., Prott, F. J., Gatta, G., McGurk, M., & Licitra, L. (2010). Major and minor salivary gland tumors. Critical reviews in oncology/hematology, 74(2), 134–148. https://doi.org/10.1016/j.critrevonc.2009.10.004
- https://www.britannica.com/science/human-digestive-system/Salivary-glands
- Parkin DM, Whelan SL, Ferlay J, Teppo L, Thomas DB. Cancer incidence in five continents, vol. VIII. IARC Scientific Publications No. 155. Lyon: IARC Press; 2002.
- Carvalho, A. L., Nishimoto, I. N., Califano, J. A., & Kowalski, L. P. (2005). Trends in incidence and prognosis for head and neck cancer in the United States: a site‐specific analysis of the SEER database. International journal of cancer, 114(5), 806-816.
- Son, E., Panwar, A., Mosher, C. H., & Lydiatt, D. (2018). Cancers of the Major Salivary Gland. Journal of oncology practice, 14(2), 99–108. https://doi.org/10.1200/JOP.2017.026856
- Kress E, Schulz HG, Neumann T. [Diagnosis of diseases of the large salivary glands of the head by ultrasound, sialography, and CT-sialography. A comparison of methods] HNO. 1993 Jul;41(7):345-351. PMID: 8376181.
- Matsuda, Y., Jayasinghe, R. D., Zhong, H., Arakawa, S., & Kanno, T. (2022). Oral Health Management and Rehabilitation for Patients with Oral Cancer: A Narrative Review. Healthcare (Basel, Switzerland), 10(5), 960. https://doi.org/10.3390/healthcare10050960
