Does Seed Migration Increase the Risk of Second Malignancies in Prostate Cancer Patients Treated With Iodine-125 Loose Seeds Brachytherapy?

Purpose: To evaluate the risk of second malignancies after migration of seeds (MS) in prostate cancer patients treated with ¹²⁵ I loose seeds brachytherapy.
Methods and Materials: Data from 2802 prostate cancer patients treated with ¹²⁵ I loose seeds brachytherapy in 3 Canadian centers were reviewed. After seeds implant, all patients underwent postimplant pelvic radiography and computed tomography scan for postimplant dosimetry. These images were used to assess whether seed migration occurred. The incidence of second malignancies was determined through the review of patient charts. The 7- and 10-year cumulative incidences of second malignancies and their 95% confidence intervals (CIs) were calculated. Fine and Gray competing risk regression analysis was used to assess the factors associated with the development of second malignancies.
Results: Mean age and median follow-up were 63.5 years and 74 (range, 12-246) months, respectively. Migration of seeds occurred in 263 of 2802 patients (9.4%). Second malignancy occurred in 87 patients (3.1%) for the entire cohort and was not different between patients who experienced MS (9, 3.4%) and those who did not (78, 3.1%) (P = .755). The 7-year cumulative incidence rates of second malignancies were 2.95% (95% CI 1.20%-6.00%) (with MS) versus 2.82% (2.10%-3.70%) (without MS) (P = .756). The corresponding values at 10 years were 6.16% (2.20%-12.3%) versus 4.51% (3.20%-5.50%) (P = .570). Migration of seeds did not seem to be a significant predictive factor for second malignancies development (adjusted hazard ratio 1.27 [95% CI 0.63-2.55]; P = .510). In both models, only advanced age was significantly associated with second malignancies development.
Conclusions: These results did not show an increased risk of second malignancies associated with MS after ¹²⁵ I loose seeds brachytherapy for prostate cancer patients. Longer follow-up and more events are required to better correlate MS and second malignancies.
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