5 Jun 2016

Are mammograms dangerous?

There is a common myth that mammograms cause more cancers than they detect and are therefore dangerous. The theory is that the radiation involved with a mammogram causes cell damage and cancer development. All x-rays(including mammograms) involve exposing parts of the body to x-ray radiation which allows a film or digital detector to show up the anatomy and possible abnormalities within. Radiation, in high enough doses does indeed damage cells and can induce cancer. The proof for this was learnt from the atomic bomb blasts in Hiroshima and Nagasaki in 1945, after which tens of thousand of people who were exposed to the associated radiation developed cancers.

The radiation dose from an x-ray is infinitesimally smaller than nuclear fall-out. In fact the background radiation that each of us who live on the highveld is exposed to each year is roughly 6 times that received during a mammogram. 

Although there is a theoretical risk of radiation from x-rays/mammograms causing breast cancer, to date there has never been a single cancer case proven to be caused by a mammogram or any other x-ray.

In general, the odds of being diagnosed with a breast cancer at mammogram are substantially higher at the first mammogram than subsequent ones. (purely a statitical likelihood of someone who's never been tested and unknowingly has a cancer in her breast). We definitely do not see a higher breast cancer rate in older patients who have had many years of mammograms.

It is estimated that the likelihood of dying from a mammogram induced breast cancer is 1 in 70,000. (theoretical since no cases are even known)The likelihood of getting a breast cancer however is 1 in 8 over the course of a woman's lifetime.

These days the vast majority of breast cancers are detected when they are grade 1(less than 2cm). This is largely due to highly sensitive tests such as mammograms done on an annual bases. The result, is a 5 year survival (prognosis) of 90%. In the days before annual mammograms the cancers were almost all larger than 2cm (ususally only found once large enough to feel) and the 5 year survival < 70%.*

Bottom line is that although there is a theoretical risk of radiation from mammograms causing cancer, it is so small that it shouldn't prevent you having an annual mammogram from age 40. We are more cautious with younger patients since immature breast tissue(women younger than 35) is thought to be more sensitive to radiation. In those patients, a sonar is done instead.

Mammograms are the best screening test we have for breast cancer. The benefits of identifying cancers early is far more valuable than the extremely remote chance of this test itself creating a cancer. 


*Obviously improvement in breast cancer treatment has also played a big role in reducing breast cancer mortality.


Hendrick, Edward R.Radiation Doses and cancer risks from breast imaging studies.Radiology.October 2010 Vol 257:1 p2951 - 2955