10/27/2025
https://www.facebook.com/share/1CivXHFDBy/
What are Interval Cancers?
Many women believe that if their mammogram is normal, they’re safe until the next one.
Unfortunately, that’s not always true. Cancers that are not found on mammograms continue to grow. They are usually discovered when they’re large enough to be felt as a lump. These are called “interval cancers.” They appear in the interval between regular mammograms, sometimes just months after a “normal” result.
They may have been missed because they may have grown very quickly or they were hidden by white dense breast tissue. Dense tissue can hide tumours on mammograms, making detection difficult. Interval cancers are often more aggressive and diagnosed at a later stage.
Why They’re So Dangerous
When cancer is missed until it becomes palpable or symptomatic, treatment becomes much harder.
Research shows that:
• These interval cancers are more likely to require chemotherapy, mastectomy, or radiation.
• Survival rates are significantly lower for interval cancers compared to those found through screening.
The Limits of Mammography
Mammography is an essential screening tool, but it has limitations. For women with the densest breasts, a mammogram can miss up to 40% of all cancers. That’s why a woman can be told her mammogram is normal, only to discover a lump months later — an interval cancer. This is not rare. It’s happening to women across Canada every day.
What Can Be Done
Early detection saves lives — but only if we can see the cancer.
That’s why provinces like British Columbia, Alberta, Ontario, and the Northwest Territories are offer some supplemental screening — ultrasound, MRI, or contrast-enhanced mammography (CEM) — for women with dense breasts.
These technologies can find cancers that mammograms may miss. They find them when they’re small. When treatment is simpler. When lives can be saved.
What You Can Do
If your mammogram report says you have dense breasts:
• Become informed.
• Talk to your provider about additional screening options like ultrasound, MRI, or CEM.
• Trust your instincts — if something feels or looks wrong, ensure you have follow-up- even if you have just recently had a ‘normal’ mammogram. Don’t ever be dismissed.
At Dense Breasts Canada:
We believe every woman deserves the best chance at early detection — regardless of where she lives or how dense her breasts are.
We’re advocating for:
• Access to supplemental screening across all provinces and territories;
• Education about breast density for healthcare providers and the public;
Because no woman should lose her life to an interval cancer that could have been found earlier.
