Diagnosis of Cowper's glands on prostate needle biopsy

The presence of normal anatomic structures may be a source of confusion to the pathologist examining prostatic needle biopsies. The morphologic features of Cowper's (bulbourethral) glands incidentally biopsied during transrectal sampling of the prostate have not been described. We reviewed seven cases of Cowper's glands found in prostatic core biopsy specimens. Sections containing Cowper's glands were stained with hematoxylin-eosin, mucicarmine, periodic acid-Schiff's-digest (PAS-D), and antibodies directed at high-molecular-weight cytokeratin (HMWCK), prostate-specific acid phosphatase (PSAP), prostate-specific antigen (PSA), Ulex europaeus agglutinin, and muscle-specific actin. Histologically, Cowper's glands resemble mucinous minor salivary glands entrapped within fascicles of muscle. Lobules of acini composed of cells distended with mucin (mucicarmine and PAS-D positive) were admixed with ducts and ductules composed of hybrid cells with both mucinous and ductular epithelial features. The HMWCK was strongly reactive with the ductular epithelium and demonstrated an attenuated cell lining at the periphery of lobules. The mucinous cytoplasm reacted with U. europaeus, whereas the ductal elements failed to stain. PSAP stains were negative, with PSA positive in most cases. Muscle-specific actin was positive in three cases. Cowper's glands occasionally may be sampled by transrectal needle biopsy. Recognition of this anatomic structure will allow discrimination from low-grade prostatic adenocarcinoma, foamy gland carcinoma, mucinous metaplasia of prostate glands, and atypical glands of undetermined significance.