Please follow along with a little bit of math:
There are 2.46 or rounded, 2.5 million women in Canada between the ages of 40-49.
Source: Stat Can website
I had first heard that 30% of women in that age range have dense breasts, so then approximately 750,000 women in Canada between the ages of 40-49 have dense breasts, however after more research I found a review of this study called "The Relationship of Mammographic Density and Age: Implications for Breast Cancer Screening" by Checka CM, Chun JE, Schnabel FR, Lee J, and Toth H., reported in March 2012. In the summary of the results, they found, "74% of patients between 40 and 49 years old had dense breasts. This percentage decreased to 57% of women in their 50's. However, 44% of women in their 60's and 36% of women in their 70's had dense breasts as characterized on their screening mammograms."
Let me do the calculation again, if we take 74% of the 2.5 million Canadian women between 40-49 then an astounding 1,850,000 or 1.85 million women have breast density that could impact the accuracy of mammogram screening.
In the book about breast cancer I was given to read it says approximately 25% of cancers are missed in women between the ages of 40-49. Using 25% to calculate then, 462,500 cancers could potentially be missed by screening mammograms.
(If you want to be conservative and take the 30% density figure, and the 25%, that is 187,500 women at risk).
The National Cancer Institute has a page on mammograms and explains both false postives (radiologists think the mammogram shows a cancer but upon further testing no cancer is present) and false negatives (a mammogram appears normal although breast cancer is present). They state that overall screening mammograms miss about 20% of breast cancers and the main cause of false negatives is high breast density. They also explain that false negative results occur more often in younger women because younger (premenopausal) women are more likely to have dense breasts than older women.
Please don't get me wrong, although about 25% of cancers are missed in women 40-49, there are many cancers that are detected by mammograms and mammograms do save lives. Please make sure you go and get your mammogram but also to ask about your breast density.
For the "heads up" of knowing to ask, which I never knew to do, I ask you please sign this petition.
Other interesting information can be found at:
Canadian Breast Cancer Foundation website - Breast Cancer in Canada, 2013