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

Purpose: 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.

Methods: 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.

Results: 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).

Conclusions: 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.