Differential expression of CK 19 in follicular adenoma, well-differentiated tumour of uncertain malignant potential (WDT-UMP) and follicular variant of papillary carcinoma.

OBJECTIVE To see the expression of cytokeratin 19, a proven helpful marker for the differential diagnosis of neoplastic follicular patterned lesions of thyroid. METHODS This was a retrospective study carried out in the Department of Pathology, Basic Medical Sciences Institute, Jinnah Postgraduate Medical Centre, Karachi from 2000 to 2005. The haematoxylin and eosin (H&E) stained sections were reviewed and the cases were classified according to already published criteria. On the basis of the recent recommendations by Chemobyl Pathologists Group, encapsulated follicular patterned lesions with questionable nuclear changes were categorized as well - differentiated tumours of uncertain malignant potential (WDT-UMP). Formalin fixed paraffin embedded tissues of follicular adenoma, WDT-UMP and follicular variant of papillary carcinoma were obtained for CK 19 immunostaining. RESULTS All (16) cases of follicular adenoma were negative for CK19. In a total of 35 cases of WDT- UMP, 10 cases scored 3+ positive for CK19, 15 were 2+ positive and remaining 10 cases were 1+ positive. There were 43 cases of follicular variant of papillary carcinoma with 4+ CK 19 positivity, 14 were 3+ positive and 3 were 2+ positive. CONCLUSION CK19 is a good and useful diagnostic marker for differential diagnosis of follicular adenoma, WDT-UMP and follicular variant of papillary carcinoma. The recommendations by Chornobyl Pathologists Group need to be adopted and the cases of WDT-UMP require strict follow-up.