Radiation therapy increases the risks of future cancers

The risk is low, but you should discuss it with your doctor.

Standard treatment for localized prostate cancer — meaning cancer that is confined to the prostate gland — is to kill or shrink tumors with radiation. Long-term results for most men treated this way are excellent. But as with other cancer treatments, radiation involves some risk, including the possibility of causing secondary cancers to form later in the body.

Secondary cancers are defined according to whether they meet certain criteria:

  • they are different from the cancer for which the patient was originally treated
  • they appear in the irradiated area
  • they were not present before the start of radiotherapy
  • occur at least four years after the end of treatment.

Historical evidence shows that secondary cancers are rare. Now, a large study of men treated with current radiation delivery methods used in the modern era has updated that conclusion.

Research data and findings

Researchers reviewed data from 143,886 men who were treated for localized prostate cancer at Veterans Affairs medical facilities between 2000 and 2015. The men were 60 to 71 years old and of various racial and ethnic backgrounds. Among them, 52,886 were treated with radiation within a year of diagnosis. The remaining 91,000 men opted for either surgery in a similar timeframe or chose to have their cancer monitored and treated only when – or if – routine check-ups showed signs of progression.

After an average follow-up of nine years, 3 percent of men treated with radiation developed a second cancer, compared with 2.5 percent of men who chose other options. The four most common types of cancer—in order of frequency of detection—are bladder cancer, leukemia, lymphoma, and rectal cancer. The risk of developing these secondary cancers increases steadily over time, peaking five to six years after radiation treatment is completed.

Dr. Oliver Sartor, an oncologist at Tulane University School of Medicine in New Orleans who was not involved in the study, says the potential for secondary cancer is an important issue men should discuss with their doctors when evaluating treatment options.

Risk of weighing

Unfortunately, doctors have only a limited ability to predict which men treated with radiation are at greatest risk of a second cancer. Smoking is a major risk for bladder cancer, “so men who smoke while undergoing radiation have another reason to quit,” says Dr. Sartor. Men with an inherited risk of Lynch syndrome (a type of colorectal cancer) also face higher risks from radiation. These men have gene mutations that make it difficult for their cells to repair DNA damage.

Noting that Dr. Sartor makes excellent and applicable points, Dr. Mark Garnick, Gorman Professor of Medicine at Harvard Medical School and Deaconess Beth Israel Medical Center and editor of Harvard Health Publishing Annual Report on Diseases of the Prostate, agrees that patients considering radiation should be informed that the treatment exposes them to a small but real lifetime risk of secondary cancers, particularly of the rectum and bladder, which may occur years after radiation therapy is completed.

Dr. Garnick says he is reluctant to consider radiation in men with a history of inflammatory bowel disease such as ulcerative colitis, who are also at greater risk of developing abdominal cancer. He also advises older men who have been treated with radiation for prostate cancer to check with their doctors before stopping routine colorectal screening.

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