Radiation therapy increases the risk of future cancers

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

A standard treatment for localized prostate cancer – that is, cancer confined to the prostate gland – is to kill or shrink the tumors with radiation. The long-term results for most men treated this way are excellent. But as with other cancer treatments, radiation therapy carries some risk, including the possibility that it could lead to the formation of secondary cancers in the body later.

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

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

Historical evidence shows that secondary cancers rarely occur. Now, a large study of men treated with current methods of radiation delivery used in the modern era updates that finding.

Study data and results

Investigators looked at data from 143,886 men who were treated for localized prostate cancer at Veterans Affairs medical facilities between 2000 and 2015. The men were between the ages of 60 and 71 and came from a variety of racial and ethnic backgrounds. . Of these, 52,886 were treated with radiotherapy within one year of diagnosis. The other 91,000 men either opted for surgery over a similar period or opted to have their cancer monitored and treated only when – or if – routine exams showed signs of progression.

After a median follow-up of nine years, 3% of men treated with radiation had developed secondary cancers, compared with 2.5% of men who chose other options. The four most common cancers – in order of their frequency of detection – were bladder cancer, leukaemia, lymphoma and rectal cancer. The risk of developing these secondary cancers increased steadily over time, peaking five to six years after radiation therapy ended.

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 cancers is an important issue that men should discuss with their doctor when evaluation of treatment options.

Risk of weighing

Unfortunately, doctors have only a limited ability to predict which radiation-treated men are most at risk for secondary cancers. Smoking is a major risk for bladder cancer, “so men who smoke while undergoing radiation therapy have yet another reason to quit,” says Dr. Sartor. Men with hereditary risks of Lynch syndrome (a type of colorectal cancer) are also at higher radiation risk. These men have genetic mutations that make it harder for their cells to repair DNA damage.

Noting that Dr. Sartor makes excellent and actionable points, Dr. Marc Garnick, Gorman Brothers Professor of Medicine at Harvard Medical School and Beth Israel Deaconess Medical Center, and Editor-in-Chief of Harvard Health Publishing Annual Report on Prostate Diseases, agrees that patients considering radiation therapy should be informed that the treatment puts them at a small but real lifetime risk of secondary cancers, particularly of the rectum and bladder, which may appear years after radiation therapy has ended.

Dr. Garnick says he is hesitant to consider radiation therapy for men with a history of inflammatory bowel diseases such as ulcerative colitis, who are also at higher risk of developing abdominal cancers. He also advises older men who have been treated with radiation therapy for prostate cancer to consult their doctor before stopping routine colorectal screening.

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