Expression of MUC1 in eosinophilic metaplasia of the prostate

Background: Eosinophilic metaplasia (EM) in the prostate is characterized by the presence of eosinophilic cytoplasmic granules in benign prostatic epithelium. These granules show exocrine-type morphology and positive expression for prostate specific antigen (PSA) and some lysosomal markers. The nature and the full immunohistochemical profile of the granules of EM have not been studied in detail yet. Aim: The aim of the current study is to investigate the expression of epithelial mucins (MUCs) in prostatic epithelium with EM. Methods: Twenty specimens from transurethral resection of the prostate (TURP) were reviewed for the presence of EM and were stained with Periodic acid-Schiff's procedure with diastase digestion (PAS.D) and immunostained with PSA and MUCs: MUC1, MUC2, MUC5AC, and MUC6. Results: The EM-foci of all prostate glands are PAS.D, PSA positive and show constant immunoreactivity for MUC1. The expression of MUC1 is with membranous and cytoplasmic localization: predominantly apical with membranous accentuation in the cases of EM with large eosinophilic granules, and perinuclear in EM with small eosinophilic granules. There is no expression of other MUCs (MUC2, MUC5AC, and MUC6) in prostatic EM. Conclusion: We report for the first time that eosinophilic cytoplasmic granules in prostatic EM are MUC1 positive and can vary in size. Based on our immunohistochemical study we suggest that EM of the prostate is not a form of mucinous metaplasia. The present results enrich the available information about the immunophenotype of EM. We assume that MUC1 might serve as a reliable and constant, although nonspecific, immunohistochemical marker of benign EM-phenotype.