A critical re-appraisal of diagnostic pitfalls in salivary gland lesions and analysis of cytokeratin 7/cytokeratin 20 as an adjunct in differential diagnosis

Background: To study the diagnostic pitfalls in fine needle aspiration cytology (FNAC) of salivary gland lesions and role of cytokeratin 7 (CK7) and 20 in differentiating various salivary gland neoplasms as an adjunct. Materials and Methods: This study included 230 cases of salivary gland lesions, which underwent FNAC at our hospital, and cyto-histological correlation was possible in 119 cases. False positive and false negative cases were identified taking histology as the gold standard and discrepant results were analyzed. Additionally, immunohistochemical staining for CK7 and 20 was done in 35 representative histological sections (including 33 malignancies and 2 benign lesions). Results: On cytology, benign tumors and nonneoplastic lesions together formed 63% and remaining 37% were malignancies. Cyto-histological correlation showed concordance rate of 80.6% and discordance rate of 19.3% with 14 false negative cases and 9 false positive cases. On immunostaining for CK, 27 of the total 33 malignancies (81.8%) exhibited CK7+/CK20 − profile. All the primary malignancies (24/25) except one were CK7+/CK20−, while majority of the secondary malignancies (5/8, 62.5%) showed CK7−/CK20 − profile. Conclusion: Although the diagnosis of most salivary gland neoplasms does not pose a problem, attention to subtle cytomorphological features and knowledge of common diagnostic pitfalls are essential to reach the correct diagnosis in a few challenging cases. Additionally, CK expression can serve as a useful adjunct to other investigations in cases of salivary gland neoplasms, to differentiate between certain commonly confused entities like, squamous cell carcinoma and high-grade mucoepidermoid carcinoma; and CK20 positive metastatic malignancy and distant unknown primary.