Breast Cancer Increases Risk for Other Cancers

Women with breast cancer have an overall 25% increased risk of developing a new non-breast cancer, according to a large new study published in the December 8, 2005, online issue of the International Journal of Cancer. Therapy may contribute to the growth of some of the new cancers.

The study, conducted by Danish researchers, involved more than 525,000 patients with breast cancer in 13 cancer registries in Europe, Canada, Australia, and Singapore. Records were analyzed for second primary cancers from the period 1943-2000, with 133,414 women followed for more than 10 years after their initial diagnosis of breast cancer.

The researchers found an almost six-fold increase of cancer risk in connective tissue of the thorax and upper limbs of women with breast cancer, which suggests that radiation therapy may play a role in developing a second cancer in organs close to the breast, such as the lungs, esophagus, and stomach. The risk of thyroid cancer was more than 60%, while the risk for ovarian cancer was 48%. Prior studies have shown a 20-30% increased risk for a second cancer in the endometrium, ovary, thyroid, lung, blood, skin, and the stomach and colon.

"The excess of cancer after a breast cancer diagnosis is likely to be explained by treatment for breast cancer and by shared genetic or environmental risk factors, although the excess of cancer suggests that there may be additional explanations such as increased surveillance and general cancer susceptibility,” wrote the authors.

On the other hand, an increased risk of endometrial cancer was shown within one year of breast cancer diagnosis, suggesting that the risk was not totally due to the therapy. Colorectal, kidney, and postmenopausal breast cancer appear to share obesity as a risk factor, while ovarian cancer and breast cancer appear to have a genetic predisposition in common.

"The overall impression from this very large study is that a breast cancer diagnosis has an effect on subsequent cancer risk in general, since so many cancer sites were seen to occur in excess of what was expected,” the authors concluded. "The known effects of treatment and common risk factors do not seem to fully explain the excesses.”

The researchers were led by Lene Mellemkjaer of the Danish Cancer Society in Copenhagen (Denmark).






Related Links:
Danish Cancer Society