The answer is still uncertain. A team of researchers at the Institute of Cancer Research in London tracked 160,900 women for an average of 11 years. The participants were divided into two groups: Women in the study group were offered annual mammography screenings beginning at age 40, while those in the control group were offered annual screenings beginning at age 50.

Deaths resulting from breast cancer among the younger women decreased by only 17 percent, a figure considered by researchers to be not statistically significant. However, the study also found that in this group of women 23 percent had at least one false-positive result, compared with 12 percent of older women. (A false-positive result is an irregularity in the screening process that later turns out not to be breast cancer.)

Regular screening also increases the risk of radiation-induced breast cancer, a risk that many endocrinologists believe outweighs the benefit in a small percentage of women.

The researchers concluded that annual mammography screenings remain too uncertain to conclude that a net benefit accrues to women in the below 50 age-group. Another study conducted by researchers at France's National Institute of Health and Medical Research (Institut National de la Sante et de la Recherche Medicale, or INSERM), found that chest X-rays may actually raise the risk of breast cancer in women with the breast cancer gene mutations BRCA1 or BRCA2.

Researchers studied 1,601 European and Canadian women with the BRCA1 or BRCA2 gene mutations, which greatly increase the risk of breast and ovarian cancers. The group included 853 women with breast cancer.

The results show that the women who reported having chest X-rays were 54% more likely to have breast cancer, compared with those who reported having no chest X-rays. That outcome was more prevalent among women up to 40 years old and those who reported having had chest X-rays before age 20.

According to the Susan G. Komen Breast Cancer Foundation's web site, the BRCA1 and BRCA2 gene mutations are carried by an estimated 250,000 women in the U.S. These inherited gene mutations account for 5 to 10 percent of breast cancers diagnosed in the U.S. A woman’s odds of developing breast cancer, assuming that she lives to the age of 85, are about 13 percent if she has no BRCA2 mutation, 60 to 80 percent if a woman has a BRCA1 mutation, and 30 to 85 percent if she has a BRCA2 mutation.

It is known that radiation exposure can increase the risk of cancer. However, it should be noted that X-rays typically use low levels of radiation that are generally considered to be safe. It is also known that the younger the age at first exposure to radiation the greater the risk of breast cancer.

The timing of exposure can be as important as the dose. When exposure occurs during the time of greater cell growth of the breast, vulnerability to the cancer-causing effects of radiation is increased. Even in older women who are still having a menstrual cycle, the timing of exposure is very important. The cumulative dose as in annual mammography screenings starting below the age of 40 in a woman with the breast cancer gene mutations BRCA1 or BRCA2 significantly increases the risk.

Breast cancer takes years to develop from the first genetic event or exposure to the point when a lump is seen on a mammogram or felt during a breast exam. It is possible that the initial genetic damage may have occurred very early in life. It is difficult to pinpoint when the initiating event occurred.

Although the medical establishment takes to avoid exposing a woman who might be pregnant to X-rays, a woman should also avoid having a mammography screening towards the end of a menstrual cycle because that's the time when the breast cells are reproducing most rapidly.

Since young women and women who are genetically at high risk for breast cancer are more affected by X-ray radiation, exposure to radiation should be limited and alternatives should be used in emergencies. Magnetic resonance imaging (MRI), which uses imaging technology different from X-rays, could be a good alternative to X-rays and mammography.

It is the responsibility of each woman to decide for herself (after research) whether she should risk developing breast cancer as a result of routine mammography screenings or risk having the complications of late-diagnosed breast cancer that could have been avoided if detected earlier by screening mammography.