Second primary malignancies affected 10.8% of men who received I-125 brachytherapy as monotherapy for prostate cancer, researchers reported in the April issue of Clinical Oncology.
But only bladder cancer had a small increase in risk in these patients compared with the general population, with the highest risk occurring during the first 4 years of follow-up after implant, said Dr. Ann Henry and her associates at St. James’s University Hospital in Leeds, England (Clin. Oncol. 2014;26:210-5).
The investigators studied 1,805 consecutive patients who received I-125 brachytherapy as monotherapy for localized prostate cancer from 1995 to 2006 at a single public hospital. Their mean age at treatment was 63 years (interquartile range, 58-68). The researchers defined possible radiation-induced cancers as developing at least 5 years after primary radiotherapy, and with histologies distinct from prostate adenocarcinoma. The median follow-up was 8 years with 487 patients (31%) having 10 years or more.
In all, 170 patients (10.8%) were diagnosed with second primary malignancies at least 1 year after I-125 brachytherapy implant, and 77 (4.9%) were diagnosed at least 5 years after implant, the investigators said. Bladder and rectal cancers were the most common, with 10-year cumulative incidences of 1% and 0.84%, respectively.
Only bladder cancer had a standardized incidence rate that exceeded that of the general population (SIR, 1.54; 95% confidence interval, 0.96-2.46). But the increase was small, and the excess risk was slightly higher during the first 4 years of follow-up (1.69; 95% confidence interval, 0.87-3.34) than during subsequent years (SIR, 1.42; 95% CI, 0.75-2.70). For this reason, the result was probably an artifact of increased urologic surveillance not caused by brachytherapy, said Dr. Henry and her associates.
“This should not act as a deterrent to patients considering low-dose-rate brachytherapy as a treatment modality for early prostate cancer,” the investigators said.