Mammography Risks Part 2

In part 1 of this series on the risks of mammography adding to the cause of breast cancer we looked at the difference between ionizing and non-ionizing radiation that we might be exposed to in Dr. John D. Boyce’s article Ionizing Radiation and Breast Cancer Risk on the Cornell University web site at:

http://envirocancer.cornell.edu/factsheet/physical/fs52.radiation.cfm#mammog

In summary, ionizing radiation exposure comes from medical x-rays and radioactive substances. They are powerful enough to knock an electron off an atom and may cause changes in a cell’s DNA which can lead to cancer.

On the other hand non-ionizing radiation cannot knock an electron off of an atom and does not directly damage DNA. Non-ionizing radiation comes from microwave appliances, power lines, cell phones, radio and television waves and radar.

With that in mind let’s continue to explore our question:

Does the radiation exposure from the mammography x-rays contribute to the development of breast cancer?

Here’s Dr. Boyce’s introductory paragraph:

“Everyone is exposed to ionizing radiation from natural and medical sources. In fact, ionizing radiation may be the most studied cancer causing agent in humans with scientific committees on radiation continuously reviewing and evaluating adverse health outcomes for over 70 years. The female breast is known to be highly susceptible to the cancer-causing effects of radiation when exposure occurs before menopause. This fact sheet will discuss what is known about radiation induced breast cancer and what factors influence or modify the effects of exposure. Most people are not exposed to the high levels of radiation that are known to cause breast cancer, and accordingly, radiation is not considered a major cause of breast cancer. Although unnecessary exposures should be avoided, diagnostic or therapeutic procedures should not be refused because of possible radiation risk.”

Here are his points to substantiate that introduction:

Is ionizing radiation a cause of breast cancer?

Yes in women exposed to high doses of radiation such as:

• the female survivors of the atomic bombings in Japan during World War II
• women given radiation therapy to treat Hodgkin’s disease and both malignant and benign breast disease
• girls treated as infants or children for several non-malignant conditions such as enlarged thymus glands
• young adolescents and women who received large numbers of diagnostic x-ray examinations to monitor tuberculosis treatments or to monitor the curvature of the spine during treatment for severe scoliosis.

What have all these studies shown about radiation-induced breast cancer?

1. Female breast tissue is highly susceptible to radiation effects
2. It takes a minimum of about 5-10 years for a radiation-induced breast cancer to develop
3. Greater levels of radiation exposure lead to greater risk of breast cancer, i.e., there is a direct dose and effect relationship
4. A woman’s age at the time of exposure is also very important.

What are the important characteristics of radiation-induced breast cancer?

First, the breast tissue of young women is one of the most sensitive tissues to the carcinogenic action of ionizing radiation.

Second, it takes a minimum of about 5-10 years after exposure before a radiation-induced breast cancer would develop, and usually many more years.

Third, no matter how low the dose, there is some small risk associated with the exposure. Fortunately, for a very small exposure, the risk is essentially negligible and would not be related to detectable increases in breast cancer risk even if millions of women were studied. Nonetheless, it is important to minimize all unnecessary radiation exposure.

Fourth, age at exposure is one of the most important determinants of the future risk of developing breast cancer due to radiation later in life. Young girls are at highest risk and women irradiated around the menopausal ages are at low risk. In fact, for exposure after the age of about 45 years there is little evidence that radiation increases the occurrence of breast cancer.

Why might this be so?

One theory is that for radiation damage of breast tissue to develop into a cancer, there is the need for estrogen stimulation and tissue proliferation that occurs during monthly menstrual cycles. Once the menopausal ages have been reached, there is a decrease in this tissue proliferation and damaged cells fail to develop into cancers.

Conversely, when a young girl is exposed to radiation, she will have menstrual cycles for several decades that might enhance the development of any underlying damage caused by the radiation. There is evidence to suggest that exposure to the immature breast during early development, and around the age of beginning menstruation, carries a higher risk than at other times of a woman’s life.

Fifth, the vast majority of persons exposed to radiation do not develop a cancer related to this exposure. Even among the nearly 25,000 female atomic bomb survivors in Japan who have now been followed for over 50 years, only 173 breast cancer deaths occurred and only 41 (or 24 percent) were attributed to the radiation received in 1945.