The association between prostate size and Gleason score upgrading depends on the number of biopsy cores obtained: Results from the Shared Equal Access Regional Cancer Hospital Database

OBJECTIVE: To test the hypothesis that the association between prostate size and risk of Gleason grade upgrading varies as a function of sampling. PATIENTS AND METHODS: We examined the association between pathological prostate weight, prostate biopsy scheme and Gleason upgrading (Gleason ≥7 at radical prostatectomy, RP) among 646 men with biopsy Gleason 2-6 disease treated with RP between 1995 and 2007 within the Shared Equal Access Regional Cancer Hospital Database using logistic regression. In all, 204 and 442 men had a sextant (six or seven cores) or extended-core biopsy (eight or more cores), respectively. Analyses were adjusted for centre, age, surgery, preoperative prostate-specific antigen level, clinical stage, body mass index, race, and percentage of cores positive for cancer. RESULTS: In all, 281 men (44%) were upgraded; a smaller prostate was positively associated with the risk of upgrading in men who had an extended-core biopsy (P < 0.001), but not among men who had a sextant biopsy (P = 0.22). The interaction between biopsy scheme and prostate size was significant (P interaction = 0.01). CONCLUSIONS: These data support the hypothesis that the risk of upgrading is a function of two opposing contributions: (i) a more aggressive phenotype in smaller prostates and thus increased risk of upgrading; and (ii) more thorough sampling in smaller prostates and thus decreased risk of upgrading. When sampled more thoroughly, the phenotype association dominates and smaller prostates are linked with an increased risk of upgrading. In less thoroughly sampled prostates, these opposing factors nullify, resulting in no association between prostate size and risk of upgrading. These findings help to explain previously published disparate results of the importance of prostate size as a predictor of Gleason upgrading.