Some forms of low-dose radiation treatment may increase the risk of breast cancer, particularly in genetically susceptible women, according to a report in the International Journal of Cancer.

Moderate- to high-dose radiation therapy has been shown to increase the risk of breast cancer, the authors explain, but it remains uncertain whether the risk extends to low-dose radiation, such as diagnostic chest X-rays.

Dr. Esther M. John from the Northern California Cancer Center, Fremont, and associates investigated the association between therapeutic or diagnostic radiation exposure and breast cancer using data from the Breast Cancer Family Registry. Self-reported information was available for 2,254 breast cancer patients and 3,431 healthy women, which included the sisters of the patients or women from the general population.

Radiation treatment of a previous cancer increased the risk of breast cancer by 3.55-fold, the investigators report. They also noted a trend toward higher breast cancer risk among women who received radiotherapy for acne or other skin conditions.

Women who had diagnostic chest X-rays for tuberculosis or pneumonia had more than twice the normal risk of breast cancer.

Women who underwent radiation for heart catheterization, spine problems, gastrointestinal illness or other unspecified chest X-rays were not at increased risk for breast cancer, the researchers note.

“To our knowledge,” John and colleagues note, “this is the largest population-based case-control study conducted to date exploring associations with radiation exposure for conditions that have not been the focus of follow-up studies (i.e., radiation treatment for acne or pneumonia). Given the low prevalence of such exposures, large sample sizes are needed to detect associations in a case-control study.”

“The findings of elevated breast cancer risk in women exposed to radiation for pneumonia and acne presented here warrant further investigation,” they conclude.

SOURCE: International Journal of Cancer, July 15, 2007.