Purpose: There are many factors impacting stage migration for prostate cancer. The number of prostate core biopsies is known to increase detection of prostate cancers. It is still unknown whether the number of biopsies is an independent predictor of tumor size. This is important as a number of studies show that tumor volume is an independent predictor of cancer progression.
Materials and methods: Using the University of California, San Francisco Urologic Oncology database, a retrospective review of 378 patients undergoing radical prostatectomy by a single surgeon during 2000 to 2003 was performed. Patient and tumor specific variables including age, prostate specific antigen (PSA), number of biopsies, biopsy Gleason grade, tumor volume in the surgical specimen and surgical specimen tumor grade were studied. Univariate and multivariate statistical methods including multiple and logistic regression were used to characterize patients by the number of biopsy cores. Tests of significance to identify predictors of tumor size were based on the partial F statistic and the likelihood ratio test.
Results: A total of 317 eligible patients were studied, of whom 119 had 6 biopsies and 198 had more than 6 biopsies. The 2 groups of patients were evenly matched in terms of age, PSA and Gleason sum, with no statistically significant differences observed. On univariate analysis, mean tumor volume was larger for patients receiving 6 core biopsies vs greater than 6 core biopsies (3.85 vs 2.04 cc, p = 0.0009). Additionally, statistically significant differences were observed when comparing median tumor volumes, as well as excluding extremely large volume tumors. On multivariate analysis the number of biopsies performed (6 vs more than 6), was an independent predictor of tumor size (p = 0.006), controlling for primary Gleason score, Gleason sum, PSA as a continuous or categorical variable, year of biopsy and year of surgery.
Conclusions: The use of extended pattern prostate biopsy templates results in the detection of smaller volume prostate cancers, independent of PSA and Gleason grade. These biopsy templates have contributed to the downward stage migration of prostate cancer detection and may possibly contribute to the risk of over detection.