The Effect of Positive Biopsy Cores on the Prognosis of Patients with Intermediate Risk Prostate Cancer Treated with Cs-131 Prostate Brachytherapy

Abstract

Patients diagnosed with intermediate risk (IR) prostate cancer (PC) have a widely variable prognosis and treatment options. Favorable intermediate risk (FIR) is defined as having only 1 IR factor (Gleason Grade (GG) 2-3, PSA>10 but <20, T2b-c) and no GG3. Unfavorable intermediate risk (UIR) patients have either GG3 disease or >1 IR factors. The amount of disease, as defined by % of positive biopsy cores, has also been proposed as a risk factor, but this to be better defined. In addition, it is unknown whether only the highest GG should be considered or if any core with PC should be counted in the total number of positive cores. We report on our cohort of 299 IR PC patients who were treated with Cs-131 prostate brachytherapy (PB), all of whom have at least 24 mo of follow up and median follow up of 70.6 mo. In general, FIR patients were treated with PB alone (115 Gy) and UIR patients were treated with EBRT (45 Gy) + PB (85 Gy). We stratified patients based on their % of positive cores to determine the effect of this on outcome. The Kaplan-Meier method was used to estimate actuarial event-time probabilities for biochemical progression free survival (bPFS), which was defined as the absence of a serum PSA that rose at least 2 ng/mL greater than post-treatment nadir PSA. 164 patients were FIR and 135 were UIR. 203 had GG2 histology and 96 had GG3. Patients with GG2 trended toward a higher 5-year bPFS of 95.9% (SE 0.015) when compared to GG3 patients who had a 5-year bPFS of 87.3% (SE 0.041) (p = 0.065). Looking at the cohort of patients with GG2 disease, patients with <50% cores positive for GG2 disease (n = 178) had a 5-year bPFS of 95.3%, with 81.9% of those patients receiving PB alone. Patients with > 50% cores positive for GG2 disease (n = 25), had a 5-year bPFS of 100% with 80% of those patients receiving EBRT + PB. In the group with GG3, patients with > 50% cores positive for GG3 trended toward a worse outcome (5-year bPFS of 82.1%) compared to those with <50% positive (5-year bPFS = 89.4%) (p = 0.095). In patients treated with Cs-131 PB, those with GG2 disease have an excellent prognosis, regardless of % of biopsy cores positive for PC. Patients with GG3 and < 50% of cores positive also have an excellent prognosis, while patients with GG3 and >50% of cores positive seem to have a worse prognosis and likely would benefit from more aggressive treatment, such as trimodality therapy.