Usefulness of immunoperoxidase staining with high-molecular-weight cytokeratin in the differential diagnosis of small-acinar lesions of the prostate gland.

There are a number of benign, small-acinar lesions in the prostate gland that may be difficult to differentiate from small-acinar adenocarcinoma. An important diagnostic criterion in this differentiation is the loss of the basal layer in small-acinar adenocarcinoma and its preservation in benign conditions. A monoclonal antibody to high-molecular-weight cytokeratins (34 beta E12) has been shown to stain these basal cells preferentially. To assess the usefulness of this antibody in distinguishing benign from malignant small-acinar lesions, we examined 21 cases of small-acinar adenocarcinoma and 47 examples of benign lesions, which included atypical adenomatous hyperplasia, atrophy, post-sclerotic hyperplasia, basal cell hyperplasia, and fibroepithelial nodule. Positive staining with 34 beta E12 was seen in 13/13 cases of atypical adenomatous hyperplasia, although in some cases the staining was weak and focal. Positivity with 34 beta E12 was also demonstrated in all other benign lesions studied. All 21 cases of small-acinar adenocarcinoma showed no reactivity with 34 beta E12. The results suggest that 34 beta E12 is of value in distinguishing between well-differentiated, small-acinar prostatic adenocarcinoma and its mimics. However, care is needed in interpretation of staining in formalin-fixed material due to the variable reactivity, particularly in cases of atypical adenomatous hyperplasia.