We performed dual-color immunostaining with a 3-antibody cocktail (α-methylacyl coenzyme-A racemase, CK34betaE12, and p63) on prostate biopsies from 200 patients. Current practice (hematoxylin and eosin staining followed by dual-color immunostaining on selected cases) was compared with a protocol in which routine dual-color immunostaining was provided in all cases. In the original pathology reports, adenocarcinoma was diagnosed in 87/200 (43%) patients. Small foci interpreted as putative cancers were detected with dual-color immunostaining in 14/113 patients who were originally diagnosed with a nonmalignant lesion. All of the suggested cancerous foci were independently reevaluated by 5 pathologists. A diagnosis of adenocarcinoma was assessed by consensus in 8 cases, and atypical small acinar proliferation was diagnosed in 1 case. Consensus was not reached in 5 cases. Six of the foci reclassified as cancer were of Gleason score 3 + 3 = 6, while 2 were graded as Gleason score 4 + 4 = 8. The feasibility of routine dual-color immunostaining was also tested by analyzing the time spent on microscopic assessment. Because small, atypical lesions expressing α-methylacyl coenzyme-A racemase (blue chromogen) were easy to detect using dual-color immunostaining, the microscopic analysis of dual-color immunostaining and hematoxylin-eosin staining was faster than that of hematoxylin-eosin staining alone that was later followed by dual-color immunostaining in selected cases (median 251 seconds versus 299 seconds, P < .0001). We concluded that routine dual-color immunostaining of all prostate biopsies would produce better diagnostic sensitivity with a smaller microscopy workload for the pathologist. However, minute foci interpreted as cancer with dual-color immunostaining need to be confirmed with hematoxylin-eosin staining, and minimal criteria for a definitive diagnosis of cancer are still lacking.
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