Taken together, our data indicate that the determination of CK-19 concentration in cyst fluid by the CYFRA 21–1 assay can be an effective complementary tool to routine FNAB for discrimination of cPTC from benign thyroid cysts, which is in agreement with meta-analysis data suggesting CK-19 as a marker of thyroid malignancy [8]. Here, KRT19 is linked to thyroiditis.