Validation of the NCCN prostate cancer favorable- and unfavorable-intermediate risk groups among men treated with I-125 low dose rate brachytherapy monotherapy.

To validate the 2019 NCCN subgroups of favorable- and unfavorable-intermediate risk (IR) prostate cancer among patients treated with brachytherapy, who are underrepresented in the studies used to develop the 2019 NCCN classification. We included all 2,705 men treated with I-125 LDR brachytherapy monotherapy at a single institution, and who could be classified into the 2019 NCCN risk groups. Biochemical failure and distant metastasis rates were calculated using cumulative incidence analysis. Of 1,510 IR patients, 756 (50%) were favorable-IR, and 754 (50%) were unfavorable-IR. Median follow up was 48 months (range, 3-214). As compared to favorable-IR, the unfavorable-IR group was associated with significantly higher rates of biochemical failure (HR, 2.87; 95% CI, 2.00-4.10; p < 0.001) and distant metastasis (HR, 3.14; 95% CI, 1.78-5.50, p < 0.001). For favorable-IR vs. unfavorable-IR groups, 5-year estimates of biochemical failure were 4.3% (95% CI, 2.6-6.1%) vs. 17.0% (95% CI, 13.6-20.5%; p < 0.001), and for distant metastasis were 1.6% (95% CI, 0.5-2.6%) vs. 5.4% (95% CI, 3.3-7.4%; p < 0.001), respectively. Patients with one unfavorable-intermediate risk factor (unfavorable-IRF; HR, 2.27; 95% CI, 1.54-3.36; p < 0.001) and 2-3 unfavorable-IRFs (HR, 4.42; 95% CI, 2.89-6.76; p < 0.001) had higher biochemical failure rates; similar findings were observed for distant metastasis (1 unfavorable-IRF: HR, 2.46; 95% CI, 1.34-4.53, p = 0.004; 2-3 unfavorable-IRFs: HR, 4.76; 95% CI, 2.49-9.10, p < 0.001). These findings validate the prognostic utility of the 2019 NCCN favorable-IR and unfavorable-IR prostate cancer subgroups among men treated with brachytherapy. Androgen deprivation was not beneficial in any subgroup. Alternative treatment intensification strategies for unfavorable-IR patients are warranted.

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