Perineural invasion (PNI) and post-treatment PSA levels at 12 months strongly predict long-term PSA relapse-free survival (PRFS) after definitive brachytherapy seed implantation for prostate cancer (PCa), according to a study.

William Ding, MD, of California Pacific Medical Center in San Francisco, and colleagues studied 204 patients with localized PCa not previously treated with hormonal therapy. The subjects, who had a median age of 69 years, underwent I-125 or Pd-103 brachytherapy seed implantation. The median follow-up was 80 months.

The five-year PRFS for patients with PSA levels of 1 or less, 1.01-2.00, 2.01-3.00, and greater than 3.00 ng/mL at 12 months was 98.5%, 85.7%, 61.5%, and 22.2%, respectively, the investigators reported in the International Journal of Radiology, Biology, Physics (published online ahead of print). The 10-year PRFS for patients with PSA levels of 1.00 or less and 1.01-2.00 at 12 months was 90.5% and 85.7%, respectively.

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In multivariate analyses, patients with a PSA level of 1.01-2.00, 2.01-3.00, and greater than 3.00 at 12 months had a 4.96, 27.57, and 65 times increased likelihood of long-term PSA relapse compared with men whose 12-month post-treatment PSA level was 1.00 or less. The presence of PNI was associated with 6.1 times increased risk of long-term PSA relapse compared with the absence of PNI.

Dr. Ding and his colleagues propose that in addition to traditional high-risk features, “the presence of positive PNI may play an important role in the standard risk assessment.”

Because of the risk of perineural spread, the addition of an external radiotherapy boost to the at-risk periprostatic tissues or adding hormonal therapy may potentially provide a benefit in local-regional control, they observed.