Should the involvement of skeletal muscle by prostatic adenocarcinoma be reported on biopsies?

Skeletal muscle is seen at the distal part of the prostate apex, where benign glands may reside as part of normal anatomy and histology, and extends more proximally anteriorly. At times, prostatic adenocarcinoma can be seen admixed with skeletal muscle, raising the question of extraprostatic extension. Although there has been increased attention regarding biopsy sampling of the distal apex to guide the performing of the apical dissection on radical prostatectomy, the finding of skeletal muscle involvement by prostatic adenocarcinoma has not been consistently reported by pathologists on biopsies. We searched our database spanning 12 years from 2000 to 2012 for all patients who had prostatic adenocarcinoma Gleason score 3 + 3 = 6 involving skeletal muscle on biopsy. We identified 220 patients who met the criteria. Of the 220 patients, 101 underwent prostatectomy, which comprised the "study group." Prostatectomy reports from these patients were compared with those of a "control group," which consisted of 201 contemporaneous patients with Gleason score 3 + 3 = 6 prostatic adenocarcinoma on biopsy without skeletal muscle involvement. The results showed a significantly higher percentage of positive margins in the study group compared with the control group (P = .006). The study group also had a higher percentage of positive margins at the apex admixed with skeletal muscle (P = .008). In summary, the findings in this study support that pathologists should report the involvement of skeletal muscle by tumor, and recommend that urologists performing radical prostatectomies on these patients try to ensure adequate excision in the apical area to avoid positive apical margin.