Head and Neck Pathol (2009) 3:69–77 Table 2 Risk stratiﬁcation of WHO [1] recognized salivary gland malignancies Low risk High Risk 71 Acinic cell carcinoma Sebaceous carcinoma and lymphadenocarcinoma Low grade mucoepidermoid carcinomaa High grade mucoepidermoid carcinomaa Epithelial-myoepithelial carcinoma Adenoid cystic carcinomab Polymorphous low grade adenocarcinoma Mucinous adenocarcinoma Clear cell carcinoma Squamous cell carcinoma Basal cell adenocarcinoma Small cell carcinoma Low grade salivary duct carcinoma (low grade cribriform cystadenocarcinoma) Large cell carcinoma Myoepithelial carcinoma Lymphoepithelial carcinoma Oncocytic carcinoma Metastasizing pleomorphic adenoma Carcinoma ex pleomorphic adenoma (intracapsular/minimally invasive or with Carcinoma ex pleomorphic adenoma (widely invasive or high low grade histology) grade histology) Sialoblastoma Carcinosarcoma Adenocarcinoma NOS and Cystadenocarcinoma, low gradea Adenocarcinoma and cystadenocarcinoma, NOS, high gradea a Intermediate grade variants of these tumors are controversial in the assignment of risk. For mucoepidermoid carcinoma this may depend on grading scheme used. For adenocarcinoma NOS, there is little data, but what is present suggests that intermediate grade should be placed in the high risk group b Adenoid cystic carcinomas are all considered high risk in terms of local recurrence, but only solid adenoid cystic carcinoma (i.e. high pattern grade) is considered high risk for nodal metastasis Fig. 1 Minimally invasive carcinoma ex pleomorphic adenoma. The pleomorphic adenoma component with sclerosis is seen on the right, and the minor low grade carcinoma component inﬁltrates the surrounding adipose tissue. This carcinoma was immunophenotypi- cally a myoepithelial carcinoma (stains not shown) Thus ‘carcinoma ex pleomorphic adenoma’ in current practice is not sufﬁcient as a stand alone diagnosis. Rec- ommendations for reporting on these tumors are: • • • Histologic type/grade Percentage of carcinoma Extend of invasion of the carcinomatous component (intracapsular, minimally invasive, and invasive). For more common malignancies however, grading sys- tems have evolved and applied with some degree of efﬁcacy. The two major named tumor types that are consistently graded in current practice are adenoid cystic carcinoma, and mucoepidermoid carcinoma. Additionally, adenocarcinoma NOS and cystadenocarcinoma, are also typically assigned a grade, though these tumors are not common enough to generate a formal system. Finally, grading of acinic cell carcinomas is somewhat controver- sial. Typically considered a ‘low risk’ tumor, many studies suggest an unusually high rate of lymph node metastasis as compared to other low risk tumors. Additionally histologic studies actually point to the ability to stratify these tumors based on cytomorphologic grading parameters [6, 7] sug- gesting that a grading system is necessary for these tumors. Adenoid Cystic Carcinoma Adenoid cystic carcinoma is a biphasic (composed of ducts and basal/myoepithelial cells) salivary gland malignancy characterized by tubular cribriform and or solid growth patterns. The biologic course of this tumor overall is slow but relentless—5 year survival is favorable at roughly 75–80%, but 15 year survival is poor at about 35% [8, 9]. Adenoid cystic carcinoma is unusual in that it is cytolog- ically fairly monomorphic, yet locally quite aggressive placing it in a ‘high risk’ category with regard to the use of adjuvant radiation. In contrast, the likelihood of lymph node involvement may be as low as 5%, and many insti- tutions consider this tumor ‘low risk’ for lymph node metastases and thus do not perform neck dissection if clinicoradiographically node negative [3]. Grading of adenoid cystic carcinoma has been shown to be prognostically useful in several series [9–11]. Unlike