Salivary gland tumors are classified into 24 types as per WHO classification [3]. They are further subdivided into low-, intermediate-, and high-grade variety based on the histopathological criteria and behavior, such as intracystic component, lymphovascular invasion, and bone invasion. The long-term survival and metastatic potential depend heavily on the tumor grade. Higher-grade tumors are associated with frequent metastases. The 5-year survival is 80–95 % for low-grade tumors and 30–50 % for high-grade tumors [2].

As mentioned the majority of salivary gland tumors are benign, and pleomorphic adenoma, a mixed tumor, is the most common type of benign tumor. The incidence of malignant tumors depends upon the type of salivary gland with a higher incidence of malignancy in minor salivary glands. In the parotid gland 20–25 % of tumors are malignant, with this incidence increasing to 40 % in the submandibular salivary gland and reaching to 90 % in the minor salivary glands [2].

Mucoepidermoid carcinoma is the most frequent malignant tumor of the salivary glands (29 %). MEC is also reported to be the most common malignant tumor of the minor salivary glands (49.8 %). Adenoid cystic tumor accounts for 26.3 % of malignant tumors arising from the minor salivary gland. In fact MEC and ACC combined account for the majority of the malignant tumors arising from the major and minor salivary glands [1].

MEC is composed of three cell types: mucoid, squamoid, and undifferentiated. Classically MEC will have a variable composition of various cell types, but often one cell type dominates. MEC where the squamoid cell type dominates is the high-grade version and has the worst outcome, with a 5-year survival of only 30 % [1].

ACC is a highly aggressive tumor with indolent behavior. It is characterized in different subtypes based on the growth pattern: tubular, cribriform, and solid. The solid type of growth pattern is the high-grade ACC and has the worst outcome. ACC undergoes perineural invasion very early during its growth. It spreads extensively to the local lymph nodes and to the distant organs [4].

Malignant salivary gland tumors are known for both locoregional and distant metastases [4]. The incidence of distant metastasis ranges from 24 to 61 % [5]. They metastasize through perineural invasion, lymphatic spread, and hematogenous dissemination. The lung is the most common site for distant spread (75–90 %), followed by the bone, CNS, liver, and other organs [5]. Both MEC and ACC are known to metastasize to distant organs. MEC metastasizes in 10–15 % of cases and ACC in 24–31 % of patients. Metastasis from ACC is particularly of interest because the metastasis can occur early during the development of the tumor and may present years after the primary tumor has been treated. Cases have been reported where distant metastasis has been detected 10 years after the initial diagnosis of the primary tumor [6]. On most occasions, distant lesions are associated with locoregional recurrence.

Distant metastases highly depend upon the type of tumor, T-stage, and the grade of the tumor. Large tumors with higher grade tend to metastasize more frequently. Positive margins and perineural invasion on histopathological examination of the resected specimen are positive predictors of distant metastases [7].