Correlation of fine needle aspiration cytology and cell block study of category III, IV, and V (TBSRTC-2017) thyroid lesions with special reference to cytokeratin-19 immunohistochemical staining

Context: Ascertaining the role of cytokeratin-19 (CK19) and its staining pattern helps to differentiate papillary carcinoma from other thyroid lesions. Aims: To correlate fine needle aspiration cytology (FNAC) and cell block study of equivocal cases (Category III, IV, and V) with the role of CK19 staining in it. Settings and Design: A hospital-based cross-sectional observational study was designed and conducted at North Bengal Medical College and Hospital, Shusrutnagar, Darjeeling. Methods and Material: The FNAC performed and reported as per TBSRTC-2017.50 cases of Category III, IV, and V was selected for cell block study and CK19 staining followed by immunohistochemical scoring. Results: Out of 50 cases, 17 were follicular neoplasm, 21 papillary carcinoma, 6 lymphocytic thyroiditis, 1 Hürthle cell adenoma, 1 medullary carcinoma, 1 lymphoma, and 3 undifferentiated carcinomas. Among cases of papillary carcinoma, 10 showed 4+ positivity, 9 showed 3+ positivity, 2 showed focal 1+ and 2+ positivity. In the case of follicular neoplasm, 1 showed 3+ positivity, 3 cases had 1+ 2+ positivity, and 13 cases revealed negative staining. Conclusion: Role of CK19 in distinguishing papillary carcinoma of thyroid from other lesions in cytologically diagnosed Category III, IV, and V (TBSRTC-2017) cases can be demonstrated.