Skeletal muscle involvement by limited Gleason score 6 adenocarcinoma of the prostate on needle biopsy is not associated with adverse findings at radical prostatectomy

Abstract

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. Editorial Comment The histology of normal prostate glands consists of epithelial cells and stromal cells. The epithelial cells are: a) urothelial (transitional cells) in the distal portion of the ducts; b) secretory and basal cells in ducts and acini; and c) endocrine cells. In the compartment of the basal cells are located prostate stem cells. By asymmetric division these cells have the ability to self-renew and give rise intermediate (or transiently amplifying cells) that rapidly regenerate and give rise to fully differentiated secretory cells (1). In some pathologic conditions, like prostatic atrophy, it is considered that the secretory compartment presents only intermediate (or transiently amplifying cells) (2). The stromal cells are smooth muscle cells, fibroblasts, nerves, and endothelial cells. In cases of adenocarcinoma of the prostate with stromal reaction (desmoplasia) the stroma shows myofibroblasts (3). In the most distal (apical) portion of the prostate gland, skeletal fibers of the urogenital diaphragm extend into the prostate. The pathologist must be aware of this fact in order to avoid misinterpret neoplastic acini among skeletal muscle cells as extraprostatic extension. The study from Johns Hopkins showed that limited cancer involvement of skeletal muscle in biopsy specimens should not be used as a contraindication for radical pr...