By Elizabeth Ward, PhD
Cancer patients may sometimes worry that treatment for their cancer might lead to another cancer down the road. Radiation therapy (radiotherapy) is of particular concern because radiation is known to cause cancer.
A recent study published in the Lancet Oncology journal found that cancer patients who were treated with radiotherapy were more likely to develop second cancers than patients with similar cancers who didn't receive radiotherapy. Experts have known for many years that radiation therapy can increase cancer risk; however, this is the first study to compare the risk of second cancers among radiation-treated patients to a large group of similar patients who did not receive such treatment. The study estimated that about 8% of second cancers among patients who received radiation were due to the radiation, which translates to five excess cancers per 1,000 treated patients. This means that for every 1,000 patients who were treated with radiotherapy, 5 of them would have a second cancer caused by that radiation treatment.
Many types of cancer treatment can cause long-term effects, including second cancers. For example, some chemotherapy drugs increase the risk of developing leukemia, and young women who have high doses of radiation to the chest are at increased risk of developing breast cancer.
However, when cancer patients receive these treatments, their risk of serious illness and death from the cancer is much greater than the potential long term effects of the treatment. Declining cancer treatment because of fear of side effects could be very dangerous. On the other hand, when more than one type of treatment is acceptable for a cancer, patients should discuss the risks and benefits of all treatment options with their doctor to make a decision about treatment that is best for them.
As more and more patients who have been treated for cancer live for longer and longer time periods, studies have shown that some treatments are more harmful than others. Where possible, safer drugs have taken the place of more toxic ones. With radiation, doses have been reduced and/or better targeted to the cancer and not the normal tissues surrounding it.
This study did not take into account newer treatment methods. For example, a new radiation technique called intensity-modulated radiotherapy (IMRT) was introduced after the study period, so the risks associated with this form of treatment could not be evaluated. The authors of the study point out that it's important to continue to do research to understand the potential risks associated with new cancer treatments.
Of course, long-term effects of treatment are only one of the potential reasons that cancer survivors may be at increased risk of second cancers. Other reasons include inherited genetic changes that some families more likely to develop certain cancers, or exposure to a risk factor such as smoking (which causes many types of cancer).
Knowing about potential long-term health effects from their treatment is one of the many reasons that it is essential that cancer patients receive a treatment summary and survivorship plan when their treatment is complete. The plan should address the potential long term effects of treatment as well as the follow-up that is recommended for their particular cancer.
More information about the risks of second cancers can be found in the Special Section of Cancer Facts and Figures 2009.