Women who survive a bout with breast cancer are at increased risk of developing cancers of the lung, stomach, and colon, among several others, new research suggests.

The elevated risk of other cancers could be due to the treatment given to fight the breast cancer, or perhaps to a genetic predisposition to develop cancer, the researchers believe.

The findings, which appear in an online issue of the International Journal of Cancer, are based on a study of 525,527 women from 13 population-based cancer registries who were diagnosed with breast cancer and followed for other malignancies from 1943 to 2000.

Compared with the general population, breast cancer survivors were 25 percent more likely to develop a second malignancy, lead author Dr. Lene Mellemkjaer, from the Danish Cancer Society in Copenhagen, and colleagues report.

Survivors were at increased risk for stomach cancer, colorectal cancer, lung cancer, soft tissue sarcoma, melanoma, non-melanoma skin cancer, endometrial cancer, ovarian cancer, renal cancer, thyroid cancer, and leukemia. The elevated risks ranged from 22 percent for colorectal cancer to 125 percent for soft tissue sarcoma.

As the time from breast cancer diagnosis increased, so did the risk of a second malignancy. In keeping with this finding, the older a woman was when breast cancer was diagnosed, the less likely was she to develop a second malignancy.

“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 general excess of cancer suggests that there may be additional explanations such as increased surveillance and general cancer susceptibility,” the authors conclude.

SOURCE: International Journal of Cancer, online December 8, 2005.