Eosinophilic metaplasia of the prostate - A newly described lesion distinct from other eosinophilic changes in prostatic epithelium

OBJECTIVE: To describe the morphologic, immunohistochemical and ultrastructural features of large, intensely eosinophilic cytoplasmic granules in prostatic epithelial cells in the benign prostate, as well as the prevalence of this condition. STUDY DESIGN: Two hundred twenty prostate needle biopsies and 104 radical prostatectomy specimens were examined for the presence of eosinophilic granules in benign prostatic epithelium. RESULTS: We found benign prostatic cells with bright eosinophilic granules in 13 of 84 (16%) negative prostate needle biopsies, 3 of 13 (23%) needle biopsies with high-grade prostatic intraepithelial neoplasia, 15 of 123 (12%) needle biopsies with adenocarcinoma and 21 of 104 (20%) radical prostatectomy specimens. Benign prostatic cells with eosinophilic granules were more commonly seen in prostatic ductal epithelium than acinar epithelium. They were usually focal and associated with variable degrees of chronic inflammation and atrophy. They differed from neuroendocrine cells with large eosinophilic granules by supranuclear location of granules, negative immunostaining for some neuroendocrine markers and presence of large exocrine-type electron-dense granules. CONCLUSION: Eosinophilic metaplasia of the prostate appears to represent a form of nonspecific histologic change in response to altered cellular milieu in the prostate.