Definition of Insignificant Tumor Volume of Gleason Score 3 + 3 = 6 (Grade Group 1) Prostate Cancer at Radical Prostatectomy-Is it Time to Increase the Threshold?

PURPOSE We investigated the tumor volume of insignificant Gleason score 3 + 3 = 6 (Grade Group 1) prostate cancer with contemporary grading. MATERIALS AND METHODS We studied 439 consecutive radical prostatectomies with Gleason score 3 + 3 = 6 (Grade Group 1) cancer entirely submitted for histological examination. RESULTS A total of 407 cases (92.7%) were organ confined (pT2), 17 (3.9%) had a positive margin at the apex (pT2+) and 15 (3.4%) had extraprostatic extension (pT3a). Extraprostatic extension was focal in 10 cases and nonfocal in 5. pT2 and pT3 cases did not differ by age or gland weight. When total tumor volume was less than 0.5 cm3, 6 of 311 tumors (1.9%) had extraprostatic extension and 6 of 311 (1.9%) had tumor at the margin at the apex for a total of 12 significant cancers (3.8%). Tumor volumes between 0.5 and 1.0 and 1.0 and 2.0 cm3 had a similar incidence of significant cancers. Of 108 cases with a tumor volume of 0.5 to 2.0 cm3 5 (4.6%) had extraprostatic extension and 7 (6.5%) had pT2+ at the apex for a total of 12 significant cancers (11.1%). The incidence of significant cancer increased further with tumor volumes greater than 2.0 cm3. CONCLUSIONS Only 3.8% of less than 0.5 cm3 Gleason score 3 + 3 = 6 (Grade Group 1) cancers had extraprostatic extension or extended apically where surgical removal was not possible. In contrast, 11.1% of 0.5 to 2.0 cm3 cancers had these adverse features and would not have been tumors amenable to active surveillance. Our data indicate that increasing the threshold above 0.5 cm3 is associated with a significantly increased likelihood of extraprostatic extension and positive surgical margins. This should be considered in future studies of the prognostic value of tumor volume and in studies of active surveillance criteria.