Androgen deprivation therapy and the risk of colorectal cancer in patients with prostate cancer.

Purpose: Androgens are known to play an important protective role on colorectal carcinogenesis, and thus the objective of this study was to determine whether androgen deprivation therapy (ADT) is associated with an increased risk of incident colorectal cancer in patients with prostate cancer.

Methods: We conducted a population-based cohort study within the UK General Practice Research Database population which included all patients newly diagnosed with prostate cancer between 1 January 1988 and 31 December 2008, followed until 31 December 2009. Time-dependent Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95 % confidence intervals (CIs) of incident primary colorectal cancer associated with the use of ADT. Secondary analyses considered cumulative duration of use and specific ADTs.

Results: The cohort included a total of 21,503 patients, of whom 184 were diagnosed with colorectal cancer during a mean (SD) follow-up 4.0 (3.0) years (rate 2.4/1,000 person-years). Overall, use of ADT was not associated with an increased risk of colorectal cancer (HR 0.99, 95 % CI 0.73-1.35). Similarly, no association was observed in terms of duration use, although this secondary analysis may have been limited by statistical power. With respect to specific ADTs, bilateral orchiectomy was the only therapy associated with an increased risk of colorectal cancer (HR 2.50, 95 % CI 1.13-5.52).

Conclusion: Overall, the use of ADT is not associated with an increased risk of incident colorectal cancer. The increased risk observed with bilateral orchiectomy may possibly be due to the prolonged androgen suppression of this therapy.