Transition zone carcinoma of the prostate gland: a common indolent tumour type that occasionally manifests aggressive behaviour

Aims: Tumours arising in the transition zone (TZ) of the prostate gland are often well differentiated and considered clinically unimportant. We have observed examples of high-grade TZ cancers that prompted this study. Methods: Review of 654 radical prostatectomy specimens previously assessed by systematic whole organ histology identified 187 (29%) TZ cancers of which 76 (11.6%) represented the index (main) tumour. These were compared with a volume-matched group of 76 peripheral zone (PZ) carcinomas. Results: Fifty-nine of 76 TZ index carcinomas had additional minor tumours mainly located in the PZ. Compared to PZ tumours of similar size, TZ tumours had significantly lower Gleason scores, less Gleason grade 4/5 and lower rates of capsular penetration and positive surgical margins. However, within this TZ tumour group, seven carcinomas had a major Gleason grade 4 or 5 component with high rates of capsular penetration (57%) and positive surgical margins (43%). Positive anterior and bladder neck margins were more common in TZ carcinoma than peripheral tumours and transperineal biopsy was the method of choice for TZ cancer diagnosis. Conclusions: A subset of TZ carcinoma characterised by high tumour grade has a significant risk of extraprostatic spread, margin positivity and possible biochemical failure. We recommend transperineal prostate biopsy for TZ tumour diagnosis and histological sampling of the anterior TZ at radical prostatectomy, even if macroscopically normal, to detect patients at risk from aggressive TZ carcinoma.