Cytokeratin 19 expression in papillary thyroid carcinoma

The expression of cytokeratin (CK) 19 was evaluated by histochemistry in 35 patients (19 women, 16 men) with thyroid papillary carcinoma, as well as in cases with nodular goiter (three), follicular adenoma (two), and follicular carcinoma (four). Twenty patients with papillary carcinoma had no signs of metastatic growth; 15 had regional or regional/distant metastases. The expression of CK 19 was examined both in the tumor tissue and in the surrounding glandular area. In 14 cases, the contralateral, so-called tumor-free lobes also were analyzed. The results showed that CK 19 was present in all cases of papillary carcinoma (occult, intra-, and extrathyroidal) and in 80%, more than half of the tumor cells were immunostained. The intensity of the immunoreactivity varied but was often strong. There was no apparent difference in immunostaining reactivity between tumors with or without metastases. The metastatic tissue expressed CK 19 in eight of 11 cases. However, CK immunoreactivity appeared also in follicular adenomas and carcinomas and in nonneoplastic parenchymal cells, particularly in those located within or close to areas with chronic inflammation. In conclusion, our results suggest that CK 19 is of limited value as a marker for routine histopathologic diagnosis, but the presence of CK 19 immunoreactive cells should always be carefully examined, as it raises suspicion of papillary carcinoma.