According to a study published in the Journal of Clinical Oncology, rectal cancer patients treated with radiation therapy are more likely to develop second cancers, but less likely to have a rectal cancer recurrence, than patients treated with surgery alone.

The American Cancer Society estimates that over 40,000 people will be diagnosed with rectal cancer in the United States in 2005. The rectum is the last six inches of the large intestine and is located between the colon (upper half of large intestine) and the anus (lowest portion of large intestine that leads outside of the body). Treatment options for rectal cancer include surgery, radiation, and chemotherapy. Although these treatments have demonstrated benefits, they may also have short- and long-term adverse effects. In the case of radiation therapy, the long-term adverse effects are less well understood than short-term adverse effects because long-term side effects, such as second cancers, may not occur until years or decades after radiation therapy.

Some studies have indicated that radiation therapy increases the risk of developing a second cancer within the tissues that receive radiation. By understanding risks of developing a second cancer, high-risk patients can be closely monitored or screened for the particular cancer so it can be detected in its earliest stages-this offers the greatest chance of a cure.

In order to evaluate the risk of second cancers after radiation therapy for rectal cancer, researchers in Sweden evaluated data from two rectal cancer clinical trials that were conducted in the 1980s. Patients were treated with either surgery alone or surgery plus radiation therapy. None of the patients received chemotherapy. Among the 1599 patients, 115 (7%) subsequently developed a cancer other than rectal cancer. The most common sites of second cancers were the prostate, colon, and bladder. Patients who had received radiation therapy were 85% more likely to develop a second cancer than patients who were treated with surgery alone. Patients treated with radiation therapy, however, also had a decreased risk of rectal cancer recurrence. Because rectal cancer recurrences are more common than second cancers, patients treated with radiation therapy had an overall benefit in spite of the increased risk of second cancers. In one of the two studies, 20% of patients treated with radiation therapy developed a recurrence or a second cancer, compared to 31% of the patients treated with surgery alone.

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The researchers conclude that rectal cancer patients treated with radiation and surgery are more likely to develop a second cancer than patients treated with surgery alone. However, given the decreased risk of rectal cancer recurrence in patients treated with radiation therapy, radiation appears to provide an overall benefit. Since recurrences are more common than second cancers, the researchers recommend that follow-up care of rectal cancer patients focus on identifying local or distant recurrences.

Reference: Birgisson H, Påhlman L, Gunnarsson U et al. Occurrence of second cancers in patients treated with radiotherapy for rectal cancer. Journal of Clinical Oncology. 2005;23:6126-6131.

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