Expression of keratin 13 in human epithelial neoplasms.

The distribution of the 52 kDa keratin 13 was evaluated immunohistochemically, using the AE8 monoclonal antibody. Various squamous and transitional cell epithelial lesions and representative control tissues were studied. This antibody performed adequately in formalin-fixed and paraffin-embedded tissue, but like keratin immunohistochemistry in general, required protease pretreatment. Keratin 13 was found consistently in the suprabasal layers of squamous epithelia of oral cavity, tonsils, larynx, esophagus, lower female genital tract, and transitional urothelium, but it was absent in the epidermis. Generally, various forms of squamous metaplasia were AE8-positive. In dysplasia, AE8 reactivity was considerably decreased or even absent despite the presence of apparent suprabasal maturation. In differentiated squamous cell carcinomas, AE8 immunoreactivity was usually limited to a few cells in the center of the keratinized foci. However, in 10% of squamous cell carcinomas, a significant number of tumor cells was positive. Only well-differentiated urothelial carcinomas showed AE8 immunoreactivity, while poorly differentiated tumors were negative. Interestingly, a Brenner's tumor showed a high number of AE8-positive epithelial cells. Our results show that the expression of keratin 13, as immunohistochemically determined by AE8 antibody, is significantly down-regulated in squamous cell malignancies. Its possible value as an adjunct to diagnosis of dysplasia should be investigated further.