Radiation therapy may up colon cancer risk

Based on data from the Geneva Cancer Registry, men who undergo external beam radiation for prostate cancer may have an increased, though still small, risk for colon cancer compared with men who do not receive radiation for their disease.

Swiss researchers analyzed data on 1,134 men with prostate cancer between 1980 and 1998 who survived at least five years following diagnosis. Of that group, 264 were treated with external beam radiation. By the end of 2003, 19 of those men had been diagnosed with colorectal cancer, making the risk of developing this cancer 3.4 times greater among patients who received radiation than among those prostate cancer patients who opted for a different form of treatment. The risk was significantly higher for colon cancer, but not for rectal cancer.

The findings may not apply to patients who received radiation more recently, the researchers note, because treatment has become much more targeted. Patients now receive radiation that conforms to the shape of the prostate, sparing nearby structures like the colon and rectum. Even so, the researchers caution, physicians should monitor radiation patients for colorectal cancer, especially five to nine years after the initial treatment; that’s when the cancers are most likely to emerge.

SOURCE: Rapiti E, Fioretta G, Verkooijen HM, et al. Increased Risk of Colon Cancer After External Radiation Therapy for Prostate Cancer. International Journal of Cancer 2008;123:1141–45. PMID: 18546265.

Originally published Jan. 1, 2009; Last reviewed April 8, 2011.