To analyze biochemical failure-free survival and erectile dysfunction (ED) in younger men treated with prostate seed brachytherapy (PB).
Included were patients ≤ 55 years treated with PB. Erectile function at baseline and after treatment were assessed using the physician-reported CTCAE version 4.0. Biochemical failure (BF) was defined according to the Phoenix Consensus definition (PSA nadir + 2 ng/mL). The log-rank test (Kaplan-Meier method) and cox-regression analysis was used to calculate BF-free survival.
Between July 2005 and November 2020, a total of 137 patients ≤ 55 years (range 44-55 years old) were treated with PB. Median follow up was 72 months. Twenty percent had Gleason 3+4 disease and 6% a PSA >10 ng/mL. Median prostate volume was 34 cc. Actuarial biochemical failure free survival at 5, 7, and 10 years, were 98%, 95% and 89%, respectively. Five patients received local salvage treatment. On multivariate analysis, CAPRA-score (HR 4.46, 95%CI 1.76-11.33, p = 0.002) and the dosimetric measure D90 > 130 Gy (p = 0.03) were predictive of BF. Five deaths occurred in our cohort, two due to cardiovascular reasons and three due to another malignancy. At baseline, all patients were able to have erections with or without medication. At 5 years and 7 years after PB, 80% and 64% of patients had little or no ED (erections without the need for medication) respectively.
In young-onset patients treated with PB, failure rates are similar to their older counterparts. Sexual function decreases with time, even in patients with good sexual function.

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