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Context: Accurate diagnosis of malignant lesions of thyroid remains a challenge, especially when classical features are lacking on cytological examination. Aims: To evaluate the expression of Cytokeratin 19 (CK 19) on cell blocks made from thyroid swellings diagnosed as papillary carcinoma or follicular adenoma/carcinoma on fine needle aspiration cytology (FNAC) smears. Materials and Methods: Aspirates from fifty patients diagnosed as papillary or follicular lesions on FNAC were enrolled in the study. Cell blocks were simultaneously made along with aspiration using standard cell block techniques. These cell blocks were subjected to Cytokeratin 19 immunoassay using immunoperoxidase ABC (avidin biotin complex). Statistical Analysis Used: Chi-square test for statistical significance and Goldman test for sensitivity and specificity. Results: Evaluation of the expression of Cytokeratin 19 on cell blocks revealed that almost all papillary thyroid carcinomas stained strongly positive while all follicular adenomas and follicular carcinomas were found to be negative for CK 19 immunostaining. The difference in frequency of Cytokeratin 19 positive papillary carcinoma and follicular adenomas was statistically significant. The predictive value of a positive CK 19 test was found to be 100% while that of a negative test was 93.9%. Conclusions: Cytokeratin 19 immunostaining in conjunction with fine needle aspiration cell blocks can be a valuable marker in pre-operative diagnosis of papillary thyroid carcinoma along with its variants (sclerosing and follicular). This can help the clinician in formulation of treatment as papillary thyroid carcinoma is treated by radical measures as against the more conservative approach for benign follicular lesions.
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