An update on grading of salivary gland carcinomas

Abstract

Histologic grade is a significant predictor of outcome in salivary gland carcinomas. However, the sheer variety of tumor type and the rarity of these tumors pose challenges to devising highly predictive grading schemes. As our knowledge base has evolved, it is clear that carcinoma ex pleomorphic adenoma is not automatically a high grade tumor as is traditionally suggested. These tumors should be further qualified as to type/grade of carcinoma and extent, since intracapsular and minimally invasive carcinomas ex pleomorphic adenoma behave favorably. The two carcinoma types for which grading schemes are common include adenoid cystic carcinoma and mucoepidermoid carcinoma. Adenoid cystic carcinomas are graded based solely on pattern with solid components portending a worse prognosis. Occasionally, adenoid cystic carcinomas may undergo transformation to pleomorphic high grade carcinomas. This feature confers a high propensity for lymph node metastasis and should thus be reported to alert the clinical team. Mucoepidermoid carcinomas are graded in a three tier fashion based on a constellation of features including cystic component, border, mitoses, anaplasia, and perineural invasion among others. All grading schemes are somewhat cumbersome, intimidating and occasionally ambiguous, but evidence suggests that using a scheme consistently shows greater reproducibility than using an intuitive approach. The intermediate grade category demonstrates the most variability between grading systems and thus the most controversy in management. In the AFIP system intermediate grade tumors cluster with high grade tumors, while in the Brandwein system, they cluster with low grade tumors.

Keywords: Adenoid cystic carcinoma; Carcinoma ex pleomorphic adenoma; Grading; High grade transformation; Mucoepidermoid carcinoma; Salivary carcinoma.

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 immunophenotypically a myoepithelial carcinoma (stains not shown)

Fig. 2

The various patterns/grades of adenoid cystic carcinoma. a Tubular, b cribriform, c solid. All grades are cytologically monomorphic and retain small dark angulated nuclear features

Fig. 3

Adenoid cystic carcinoma with high grade transformation. a A conventional cribriform component with monomorphic nuclei on top transitions to a pleomorphic highly atypical adenocarcinoma on bottom. b The transformed component metastasized to a cervical lymph node

Fig. 4

Grading of mucoepidermoid carcinoma. a A low grade tumor demonstrating a well demarcated border, macrocystic spaces and a bland cyst lining. b An intermediate grade tumor demonstrating a more solid growth with only few microcysts, and focal infiltration. It is important to note that the Brandwein system may potentially classify this tumor as high grade (infiltration if these nests are considered ‘small enough’, and intracystic component <25% equates to 4 points), while the AFIP grading system still categorizes this tumor as low grade (score is only 2/14). c High grade mucoepidermoid carcinoma with no cystic spaces and a highly infiltrative growth pattern. Inset: showing anaplasia or pronounced nuclear atypia

Fig. 5

Oncocytic mucoepidermoid carcinoma. a This solid highly infiltrative oncocytic lesion would be classified in some grading schemes as high grade. b The tumor cells have abundant granular eosinophilic cytoplasm. c Only rare foci with mucus cells are noted. This patient suffered one recurrence 8 years after diagnosis but is currently free of disease for almost 5 years