Partial atrophy in prostate needle biopsies: a detailed analysis of its morphology, immunophenotype, and cellular kinetics.

We systematically analyzed 73 prospectively collected partial atrophy (PA) foci from over 185 prostate needle biopsy cases to characterize them along 3 fronts: morphologic, as it can be a mimic of prostate cancer (PCa), immunohistochemical (basal cell markers and alpha-methyl acyl-CoA racemase), as it often shares the staining characteristics of PCa, and cellular kinetics (MIB-1 proliferation marker), as it belongs to the larger group of focal atrophy, some of which have been shown to be proliferative and associated with chronic inflammation. The following morphologic features were prominent at low magnification: small to mid-sized glands with circumscribed (70%) or disorganized growth pattern (30%), presence of stellate/undulated gland lumina (92%), associated few completely atrophic glands within the PA focus (97%), and scant apical but abundant lateral pale/clear cytoplasm similar to adjacent benign glands (100%). On higher magnification, 33% of foci contained micronucleoli, but all lacked nuclear enlargement (100%) or macronucleoli (100%), characteristic of PCa. No adjunctive features of PCa were seen. Patchy basal cell staining was observed in 52/71 (73%), whereas 4/71 (6%) were completely negative. alpha-methyl acyl-CoA racemase demonstrated variable expression, stronger than the benign glands in 7/72 (10%) foci. Associated pathology included PCa (42%), and complete atrophy (91%), distinct from PA foci. There was no difference between the mean proliferative index of the PA foci compared with the benign glands [5.5 (range 0 to 30) and 5.6 (range 0 to 31), respectively, P=0.97 by paired t test], as measured quantitatively by ChromaVision system. PA foci were rarely associated with inflammation (1%). Familiarity with these morphologic features and staining characteristics will allow its confident separation from cancer, especially in limited biopsy material. PA foci do not represent a spectrum of proliferative inflammatory atrophy, justifying its term.