TUESDAY, March 29 (HealthDay News) -- The odds a second cancer
will develop after radiation treatment for a first cancer are
relatively low, U.S. National Cancer Institute researchers
In a long-term study of more than 600,000 cancer survivors, an
estimated 8 percent of second cancers were attributable to
radiation treatment for the original cancer, according to the
The results suggest that other factors, such as lifestyle risks
and genetics, cause the majority of second cancers, the researchers
"The findings can be used by physicians to really put the risks into perspective when they are talking treatment options with their patients," said lead researcher Amy Berrington de Gonzalez, an investigator in the NCI's radiation epidemiology branch.
Patients should feel reassured, she added. "In general, the
risks [of radiation therapy] are smaller than the benefits," she
The study, published online March 30 in
The Lancet Oncology, is the first to quantify the cancer risks posed by radiation treatment for different malignancies.
Berrington de Gonzalez and colleagues collected data on 647,672
adult cancer survivors included in the U.S. Surveillance,
Epidemiology and End Results cancer registries. All had survived
five years or longer after cancer treatment, and follow-up ran from
1978 to 2007.
The researchers looked at outcomes for 15 different types of
cancer for which radiation treatment is routine, including cancers
of the rectum, larynx, lung, breast, cervix, testicles, prostate,
eye and orbit, brain and thyroid.
Over the 30 years of follow-up, 9 percent of these participants
developed a second cancer. Of these, about 3,300 (8 percent) might
have been the result of radiation treatment, the study authors
Second cancers related to earlier radiation therapy varied by
type, the researchers noted.
More than half of the second cancers developed in breast and
prostate cancer survivors. Four percent of second cancers were in
the eye, and 24 percent were cancer of the testicles, the
Patients who had their initial cancer when young were at the
greatest risk of developing a second cancer. Also at high risk were
those whose organs received high doses of radiation. The likelihood
of developing a secondary cancer increased over time.
When these data are put in perspective, the absolute risk for a
second cancer is 3 in 1,000 over 10 years after radiation therapy
and 5 in 1,000 over 15 years, Berrington de Gonzalez said.
"We know that radiation therapy can increase the risk of getting another cancer, but at the same time the benefits outweigh the risks," said Elizabeth Ward, national vice president for intramural research at the American Cancer Society.
Radiation therapy is an important and relatively safe treatment
for cancer, she added.
Thanks to treatment advances, Ward said, radiologists today are
better able to pinpoint treatment and limit exposure to healthy
tissue than they were in the past.
Now, studies are needed to determine the cancer risks from newer
radiation treatments, the authors noted.
Dr. Anthony D'Amico, chief of radiation oncology at Brigham and
Women's Hospital in Boston, agreed that the NCI findings are
"Despite people's concerns, radiation is relatively safe with regard to the issue of second cancers, because the number of cancers that result from it are very small," D'Amico said.
For more information on radiation therapy, visit the
U.S. National Cancer Institute.