The diagnostic utility of cytokeratin 19 in differentiating malignant from benign thyroid lesions

INTRODUCTION: Thyroid carcinoma is classically diagnosed based on certain histological criteria. In some cases, definitive diagnoses may be challenging when morphological features are equivocal. This study evaluated the usefulness of Cytokeratin 19 (CK 19) as an immunohistochemical marker to differentiate the different histological types of malignant thyroid neoplasms, particularly papillary thyroid carcinoma (PTC) from benign thyroid lesions.

MATERIALS AND METHODS: We collected 54 malignant and 65 benign thyroid lesions diagnosed by histology in Universiti Kebangsaan Malaysia Medical Centre between January 2010 and December 2015. All cases were immunohistochemically stained with CK 19 and evaluated by 3 independent observers. The immunostaining patterns were scored based on the intensity and proportion of staining and finally graded as negative, weak positive, moderate positive or strong positive. In addition, the immunostaining scores of the malignant cases were correlated with their TNM pathological tumour stages.

RESULTS: Cytokeratin 19 staining expression was higher in malignant than benign thyroid lesions (p < 0.001) which was most prominent among classical PTC. The four PTC cases that showed negative or weak staining were all follicular variant of PTC. Benign conditions were mostly negative or showed weak positivity. There was no correlation between CK 19 expression and TNM primary tumour stage (pT).

CONCLUSION: Cytokeratin 19 is a useful marker in differentiating malignant from benign thyroid conditions particularly the classical PTC, provided its interpretation is by correlation with morphology and takes into consideration the intensity and proportion of positive staining.