Purpose Skeletal muscle involvement by prostate cancer is considered to be ambiguous for extraprostatic extension when it is found at the apex, where benign prostatic glands naturally blend with the skeletal muscle of the rhabdosphincter. We investigated the significance of skeletal muscle involvement by cancer in needle biopsies in predicting adverse outcomes at radical prostatectomy. Materials and Methods From 2000 to 2009, we retrospectively identified 40 cases with Gleason score 6 adenocarcinoma involving up to 20% of 1 core, with skeletal muscle involvement. Outcomes of radical prostatectomy were compared with a control group of 82 cases with the same parameters without skeletal muscle involvement from the same period. Results In radical prostatectomy specimens Gleason score greater than 6, extraprostatic extension and positive margins were found in 15.0%, 7.5% and 12.5% of patients in the study group, compared to 20.7%, 11.0% and 4.9% of patients in the control group, respectively. No statistically significant differences were found between cases with or without skeletal muscle involvement on needle biopsy. The apical margin was the only positive margin in 4 of 5 study group cases with positive margins. In contrast, positive margins were randomly distributed in the control group. Conclusions Limited cancer involvement of skeletal muscle in biopsy specimens should not be used as a contraindication for radical prostatectomy for otherwise resectable prostate cancer as most patients have organ confined disease and negative margins. However, care must be taken during division of the dorsal vein complex to avoid a positive margin on the anterior apex of the prostate.
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