Late gastrointestinal toxicity after radiation for prostate cancer.

Background: The current study was designed to determine rates and predictors of late, lower gastrointestinal toxicity after radiation therapy in a population-based cohort of older men with prostate cancer.

Methods: The study population consisted of men with localized or regional stage prostate cancer who were age > or =66 years and were diagnosed between 1992 and 1999 who were identified in the Surveillance, Epidemiology, and End Results (SEER)-Medicare database. Gastrointestinal diagnoses were ascertained through claims from 6 to 60 months after diagnosis. The relative rates of diagnoses in the radiation group versus the nonradiation group were used as a means of estimating toxicity from radiotherapy. Cox modeling was used to determine factors associated with gastrointestinal diagnoses.

Results: A total of 57,955 men were included, 24,130 of whom were treated with radiation therapy. Among patients with 5 years of follow-up, the rates of gastrointestinal diagnoses were 19.4% higher in irradiated patients than among patients who did not have local therapy. Hemorrhage was the most common diagnosis, and was increased by 18.9% among patients treated with radiation (39.6% of irradiated patients vs. comparison rates of 18.2% in patients treated with radical prostatectomy and 20.7% in patients with no local therapy). Diagnostic lower endoscopies were performed in an additional 20.9% of men (32.4% of men treated with radiation vs. 12.7% of men who underwent prostatectomy). In all, 4.4% of irradiated men were hospitalized with a gastrointestinal diagnosis versus comparison rates of 3.2% among men with no local therapy. In multivariate models, increasing patient age, hormonal therapy, comorbidity, diabetes, peripheral vascular disease, and hemorrhoids were all associated with gastrointestinal diagnoses consistent with toxicity, whereas tumor stage and grade were not predictors.

Conclusions: Lower gastrointestinal toxicity after radiation therapy for prostate cancer continues for at least 5 years and may be more common than previously reported.