Mammography raises cancer risk for genetically susceptible women

A century of experience with X-rays has taught radiologists to avoid exposing fetuses, children, and women of child-bearing age to ionizing radiation. Now, a new study from the British Medical Journal suggests women carrying the BRCA1 or BRCA2 genetic mutation have an elevated risk of breast cancer when they undergo a mammogram or chest X-ray before the age of 30.

Study author Anouk Pijpe and colleagues at the Netherlands Cancer Institute interviewed 1,993 women with known BRCA1 and BRCA2 mutations about their clinical and medical imaging histories from 2006 to 2009 to determine if exposure to radiation from mammography or chest X-ray raised their risk for breast cancer. Subjects were drawn the Netherland, France, and U.K. All were at least 18 years old.

Women with BRCA1 or BRCA2 genes are known to carry an elevated risk for breast and ovarian cancer. The American Cancer Society recommends annually screening mammography and breast MRI beginning as early as age 30 for such susceptible patients.

Researchers found a history of any exposure to ionizing radiation from mammography or chest X-rays between the ages of 20 and 29 increased breast cancer risk by 43 percent. Any exposure before the age of 20 increased breast risk by 62 percent. No correlation between breast cancer and radiation-based imaging was seen for women between ages of 30 and 39.

Overall, 43 percent of the subjects told researchers that they already had a history of breast cancer. Of the 1,993 subjects, 48 percent (926) received an X-ray, and 33 percent (637) underwent mammography during the study period.

Results suggested that radiation exposure significantly increases the risk for breast cancer onset in the third decade of life for BRCA 1/2 carriers. They showed that 15 percent of susceptible women who had one mammogram before age 30 will develop breast cancer before the age of 40, compared with a 9 percent cancer incidence rate for BRCA 1/2 women who did not have mammography during their twenties. The authors noted, however, that the finding should be interpreted with caution due to a small sample size.

Pijpe, a postdoctoral research fellow in epidemiology and biostatistics, told that the results support the recommendation to use MRI and other imaging technique that do not involve ionizing radiation imaging for screening young BRCA1 and BRCA2 women.

"While previous studies were based only on mammography or radiography, this large cohort study used estimates of an individual age-specific cumulative breast dose from various diagnostic radiation procedures as a measure of total diagnostic radiation exposure," Pijpe said.

For the general population, a two-view digital mammography exposes the patient to about 0.56 mSv of radiation, according to medical physicist Edward Hendrick, who was not involved in the study, but had a study published last month in the journal Radiology. The dose translates into an average lifetime risk of fatal breast cancer of 1.3 cases per 100,000 women aged 40 at exposure.

According to the FDA, a two-view digital chest radiogram exposes a patient to 0.1 mSv. The average person in the U.S. is exposed to about 3 mSv per year from naturally occurring radiation.

To learn more:
- check out the full study
- here's the article
- read the BMJ announcement