Using biochemical and immunohistochemical studies, alterations of cytokeratin expression has been reported in seborrheic keratosis.

To further investigate the cytokeratin expression in seborrheic keratosis, we have done immunohistochemical staining using a panel of specific anti-keratin antibodies in this study. We also observed the cytokeratin expression in the hair, sebaceous gland and sweat gland of the some epidermis.

Twenty cases of seborrheic keratosis were collected from the pathologic files. The histological types included acanthotic type (13 cases), hyperkeratotic type (5 cases), and pigmented type (2 cases). All tissues had been fixed in formalin and then paraffin-embedded according to conventional procedures. Each section was mounted on a gelatin-coated glass slide, and incubated with various anti-keratin antibodies. The sections were then immunostained using the avidin-biotin-peroxidase complex system. The peroxidase reaction was visualized with diaminobenzidine (DAB).

1. Cytokeratin expression in seborrheic keratosis lesions

On staining with 34βB4 (K1), several staining patterns in the suprabasal layers of the epidermis were observed in 10 out of 20 cases. Using the AE1 (K10,14,15), we observed focal staining in 2 cases. We observed several positive staining patterns in 5 cases with K13,16 antibody. On staining with K10 antibody, we observed focal or irregular staining patterns in 14 cases. Focal staining was also observed with K5,8 antibody in one case.

2. Cytokeratin expression in the hair, sebaceous gland and sweat gland

On immunoperoxidase staining of hair, there were positive reactions with CAM5.2 (K8,18) in 2 cases. There were positive reaction with K13,16 antibody in one case, with 34βB4 (K1), and K10 antibody in 3 cases, and with K17 antibody in 2 cases.

On immunoperoxidase staining of sebaceous glands, there was one positive reaction with CAM5.2 (K8,18) in the suprabasal cells of sebaceous glands and with K13,16 antibody in sebaceous ducts. There were positive reactions with K17 antibody in the sebaceous ducts in 2 cases, and with K1 antibody in the sebaceous glands in one case.

Using 34βB4 (K1), 4 out of 20 cases showed positive reactions in sweat glands. On staining with AE1 (K10,14,15), positive reactions were observed in 8 cases. Staining with CAM5.2 (K8,18) showed positive reactions in 14 cases. There were positive reactions with K19 antibody in 9 cases.

Our data suggests that the predominant keratin expression in the tumor cells of seborrheic keratosis is high molecular weight keratin (K1/K10) rather than other lower molecular weight keratin. Tumor cells show some proliferative activity and monoclonal antibody K19 could be a marker for eccrine sweat glands like CAM5.2 (K8,18).