PATHOLOGY

Prostate Basal Cell Lesions Can Be Negative for Basal Cell Keratins: A Diagnostic Pitfall
Zhou M, Magi-Galluzzi C, Epstein JI
Department of Anatomic Pathology, The Cleveland Clinic Foundation, Cleveland, Ohio, USA
Anal Quant Cytol Histol. 2006; 28: 125-9

• Background: Prostate basal cell lesions can have architectural and cytologic atypia that mimic prostate adenocarcinoma. Immunohistochemical stains for basal cell markers are most helpful in the differential diagnosis. All of the published studies show basal cell lesions are positive for basal cell keratins, whereas adenocarcinoma is negative for both. We reported two cases of prostate basal cell lesions with negative basal cell keratin expression by immunohistochemistry.
• Study Design: We reported the histologic and immunohistochemical profiles of two cases of basal cell lesions of the prostate.
• Results: Histologically, both cases were highly suspicious for prostate adenocarcinoma with infiltrative growth pattern and significant nuclear atypia. The atypical glands in both cases were negative for basal cell keratins. However, both lesions were positive for another basal cell marker, p63, confirming that they were basal cells in origin, rather than prostate adenocarcinoma.
• Conclusion: Prostate basal cell lesions can occasionally be negative for basal cell keratins by immunohistochemistry and therefore may be misdiagnosed as prostate adenocarcinoma. We recommend using both p63 and basal cell keratins simultaneously in the workup of atypical prostate lesions to avoid such a misdiagnosis.
  
  
• Editorial Comment
  Absence of basal cells is a hallmark for the diagnosis of prostatic adenocarcinoma. Basal cells in the prostate do not have phenotype of myoepithelial cells and this is opposite to what happens in the mammary gland. In the latter, the myoepithelial cells have function of contraction that does not happen in the prostate. The basal cells in the prostatic gland can be recognized on hematoxylin and eosin stain. They are located next to the basement membrane, the nuclei may be round, oval or pyramidal, darker than the apical cells and sometimes show a clear halo. They stain in immunohistochemistry by high-weight cytokeratins (34bE12) and p63. The first stains the cytoplasm and the latter the nuclei.
  Presence of basal cells in prostatic acini excludes adenocarcinoma but not their absence. Why does it happen? One of the reasons is disclosed by the paper of this survey. Very rarely basal cells may not stain by immunohistochemistry. Most frequently, absence of basal cells is due to the anatomical distribution in the acini. Basal cells may be continuously distributed along the acini or may be patchy or discontinuously distributed. The latter distribution frequently happens in smaller branches of the acini, which may also not show basal cells at all.
  This peculiar distribution of basal cells is of utmost importance for the proper interpretation of small foci “suspicious but not diagnostic for adenocarcinoma” (improperly called ASAP). In such small foci, basal cells may be absent due to anatomical spacing and not due to absence of true neoplastic acini.

Dr. Athanase Billis
Full-Professor of Pathology
State University of Campinas, Unicamp
Campinas, Sao Paulo, Brazil