Keratin immunoreactivity as an aid to the diagnosis of persistent adenocarcinoma in irradiated human prostates

Postirradiation prostatic biopsy is believed by many to be the best measure of radiation effectiveness in prostatic cancer. Therapeutic irradiation may induce prostatic glandular atypia, which in its severe form can be confused with persistent adenocarcinoma on prostatic biopsies. In the current study, 37 postirradiation prostate biopsy specimens were evaluated by immunohistochemistry using a specific monoclonal anticytokeratin antibody (KA1) that reacts with the basal cells of normal or hyperplastic glands, but is nonreactive with the lumenal cells or with prostatic carcinoma cells. Persistent carcinoma was observed in 19 cases in which antibody staining was absent. The noncarcinomatous glands retained reactivity, but this reactivity appeared in a new and previously undescribed pattern. The irradiated lesion was characterized by cellular pleomorphisism, with enlargement of nuclei and loss of polarity. The immunoreactivity was seen in the enlarged basal cells and was seen to focally extend to involve the lumenal cell layer. In five of 37 cases, glands were seen that were so atypical on the routinely stained sections that a distinction from cancer could not be made. These same glands in the adjacent section reacted with KA1 in each case allowing us to conclude that the changes were benign. We conclude that the interpretation of postirradiation prostatic biopsy specimens may be aided by immunohistochemistry with this anticytokeratin antibody.