Brachytherapy is a widely used treatment for localized prostate cancer (CaP) and is only appropriate as monotherapy for low-risk cancer. The predicted response to therapy is defined by the pretreatment parameters, of which the biopsy Gleason grade is central. However, the biopsy grade often misrepresents the true pathologic grade. We examined the impact of incorrect biopsy grading on brachytherapy outcomes.

We constructed a decision analytic model to assess the theoretical performance of brachytherapy for a theoretical cohort of men with Gleason score 6 CaP who underwent radical prostatectomy. The variables regarding biopsy Gleason scores and the correlation with the surgical specimen findings were generated from the institutional data. The ranges for these variables, biochemical performance of brachytherapy, costs, and disease state utilities, were obtained from a data review.

For the base case, 67% of biopsy grades correlated with the pathologic grade. With this concordance, 8% of failures could be attributed, in part, to undergrading. On the basis of the model assumptions, as concordance worsened to 50%, the rate of undergraded failures increased to 12%. After adjusting for the quality of life associated with higher-grade disease and the risk of biochemical failure, the aggregate cost of treatment of biopsy grade 6 disease was increased by 8% because of undergrading ($75,700 versus $81,500 per case). The bulk of this effect was the cost of failure among patients with undergraded disease.

Brachytherapy for Gleason score 6 disease is reported to have excellent results. Undergrading of prostate biopsies can negatively affect clinical outcomes and increase treatment costs. Although the risk is low, it should be considered when counseling patients with CaP.