by Maychai Brown

This is the first in a series intended to highlight findings documented in State of the Evidence 2008.

Ionizing radiation is reported to be the longest-established environmental cause of human breast cancer in both women and men. Exposures come from a variety of sources: X-rays, CT scans, fluoroscopy, emissions from nuclear power plants, scientific research involving radionuclides, military weapons testing, and nuclear medicine procedures.

A person's age at the time of exposure may be important. Data gathered after accidental, military and medical exposure to emissions of radiation affecting the general population demonstrate an increased lifetime breast cancer risk for both adolescents and children.

Studies on rats and human breast tumour cell cultures in vitro indicate that estrogen may act synergistically with radiation to increase carcinogenesis. According to State of the Evidence, "This is of particular concern given the widespread exposure to estrogen-mimicking chemicals in our environment and the multiple sources of ionizing radiation."

It is of limited comfort to note that improvements in mammography equipment have reduced the dose of radiation from 2 rads to 0.5 rads and that digital mammography yields one-third the dose of radiation as compared to conventional methods.

Although the report's recommendations are meant for the U. S., some are applicable to Canada. For example, medical professionals should provide people with booklets in which to keep a record of each X-ray exposure. Standards should be established requiring physicians and technicians to use the smallest dose of radiation possible to capture the highest quality image. Both recommendations are important considering that radiation damage to the genes is cumulative over a lifetime.

The report also calls for new research: "to better understand the possible cumulative, additive and synergistic effects that could result from combined exposure to toxic chemicals and ionizing radiation" and "to develop non-invasive technologies for breast cancer screening, diagnosis and treatment."

For more detail, see "Evidence Linking Radiation to Breast Cancer," State of the Evidence 2008, pp 58-60 and 65. The report is available to download at www.bcam.qc.ca/ index1.html and, in print, at the BCAM office.