Tumor Burden in Prostate Brachytherapy Patients Estimated by Individual Core Involvement and Association With Pathologic Risk Factors

Purpose: Inter-related factors such as TNM stage, pretreatment PSA, Gleason Sum (GS), presence of perineural invasion, extracapsular extension, and the percentage of positive biopsy all play a role in risk categorization for prostate brachytherapy patients. Tumor bulk may be better estimated by summing the percent involvement of the biopsy cores in each patient. Materials and Methods: Pretreatment biopsy risk factors among patients treated with radioactive implant as part of the treatment for non-metastatic prostate cancers patients were investigated. 549 patients were identified who had either low dose-rate brachytherapy (prostate seed implant) or high-dose rate brachytherapy (HDR) as part of the treatment for prostate cancer over a 10 year period (1999-2009). For 281 cases complete biopsy information by sextant or dodecant was available. For each case the percent of each core involved was recorded according to grade. The sum of the percent involvement of the cores for each case gave an estimate of tumor bulk. Results: The sextant or dodecant location of any positive biopsy appeared to be relatively randomly distributed among patients with few positive cores. As the bulk of tumor increased, so also did the grade of tumor. According to GS groups: GS 6 (n = 112), GS 7 (n = 124), GS 8 (n = 24), and GS 9-10 (n = 20), the mean pretreatment PSA values were 5.96 ng/mL, 7.65 ng/mL, 10.48 ng/mL, and 35.0 ng/mL, respectively. For the same groups the percentage positive biopsy rates were 25.8%, 39.1%, 48%, and 64%, respectively. For any positive core, the percent of that individual core that was involved according to GS group was: GS 6, 21.7%; GS7, 35.3%; GS 8, 46.7%; GS 9-10, 52.9%. Conclusions: Increasing prostate cancer tumor burden was associated with increased tumor grade per case and per needle core. Traditional prognostic factors for prostate cancer may be confounding to the effect of tumor bulk reflected as the percent of biopsy core involved with cancer.