The incidence of transition zone prostate cancer diagnosed by transperineal template-guided mapping biopsy: implications for treatment planning.

Objectives: To report the incidence of transition zone (TZ) cancer in patients undergoing transperineal template-guided mapping biopsy (TTMB) of the prostate gland.

Methods: Five hundred thirty-nine consecutive patients underwent TTMB by means of an anatomic technique with sampling of 24 defined prostate regions. The position of each biopsy core was recorded in 3 dimensions. For every patient, the location of each positive biopsy core, the number of positive cores, the Gleason score, the percentage involvement of each core, and the presence/absence of perineural invasion was documented.

Results: The median volumetric prostate volume was 56.0 cm(3) with an ellipsoid TZ volume of 20.1 cm(3). The median number of TTMB cores was 58 with a median of 11 TZ cores. Two hundred eighty-seven (53.2%) were diagnosed with prostate cancer. TZ cancer was detected in 130 (45.3%) of patients with prostate cancer but only 6 (4.6%) were confined to the TZ. Overall, 38.9% of TZ cores were positive for malignancy. Of the TZ cancers, 37 (28.5%), 64 (49.2%), and 29 (22.3%) were assigned Gleason scores 6, 7, and 8-10. Compared with a standard 12-core biopsy approach, the results of the TZ biopsy upgraded the Gleason score in 24.6% of patients. Only 4 cancers (3.1%) involving the TZ were classified as clinically insignificant.

Conclusions: Although only 4.6% of cancers were confined to the TZ, 45.3% of all prostate cancer patients had TZ involvement.