Mammograms remain one of the most effective tools for early detection of breast cancer, helping to reduce mortality through earlier diagnosis and treatment. But like any medical test, mammograms have limitations. They’re not infallible, and in some cases, they can miss signs of breast cancer, leading to false reassurance or delayed diagnosis. Understanding why this happens, and what you can do about it, is critical for your health.
How Mammograms Work
A mammogram is a low-dose X-ray used to examine breast tissue. The goal is to identify any unusual masses, calcifications, or structural changes that may signal the presence of cancer. Radiologists review the images for patterns that suggest a tumour or precancerous change.
There are two main types:
- Screening mammograms for women without symptoms.
- Diagnostic mammograms for women with a lump or other concerns.
While they are highly useful in the detection of abnormalities in breast tissue, mammograms like most things in this world are not perfect. Luckily if results do happen to be unclear your doctor will most likely send you for an additional scan to confirm results.
How Often Do Mammograms Miss Cancer?
Studies suggest that mammograms miss approximately 10–20% of breast cancers, particularly in women with dense breast tissue. This is known as a false negative—when the scan appears normal even though cancer is present.
False negatives can result in a delay in diagnosis, which may impact treatment outcomes. According to the National Cancer Institute, the chance of a false negative is higher in younger women and those with dense breasts, as dense tissue can mask tumours.
Why Would Mammograms Miss Cancer in Certain Cases?
Several factors contribute to mammograms failing to detect cancer:
1. Dense Breast Tissue
Breasts are made up of glandular, fibrous, and fatty tissue. Dense breasts contain more glandular and fibrous tissue, which appears white on a mammogram, the same colour as many tumours. This makes abnormalities harder to detect in these cases.
2. Tumour Size or Location
Smaller tumours or those located near the chest wall or under the armpit may be missed if they are outside the typical imaging range.
3. Human Interpretation
Even with digital imaging and computer-aided detection, radiologists may interpret scans differently. Subtle signs might be overlooked, especially in the very early stages of breast cancer.
4. Rapidly Growing Tumours
Some aggressive tumours grow quickly in the time between regular mammograms and may not have been present at the time of the last scan.
Are 3D Mammograms More Accurate?
3D mammography, or digital breast tomosynthesis, creates a layered image of the breast, offering a clearer view of overlapping tissue. Research shows that 3D mammograms:
- Reduce false negatives
- Improve detection rates in women with dense breasts
- Result in fewer call-backs for additional testing
At Bergman Ross, we use tomosynthesis technology—providing a clearer, more detailed view of breast tissue and increasing the likelihood of detecting cancer early, especially in women with dense breasts. While not available everywhere, 3D mammography is becoming more widely used and may be especially beneficial for women with known risk factors or dense breast tissue.
What You Can Do to Improve Detection
If you’re concerned about the accuracy of mammograms, there are several steps you can take to reduce the risk of a missed diagnosis:
- Ask About Breast Density: After your scan, ask your provider/radiologist if you have dense breasts. Many regions now require that women be notified of this, but it never hurts to ask for your own piece of mind.
- Consider Additional Imaging: Ultrasound or MRI can offer more detail in dense breast tissue. Your doctor may recommend these based on your risk profile.
- Know Your Risk Factors: Family history, genetic mutations (like BRCA1/2), and previous biopsies may warrant earlier or more frequent screening.
- Don’t Ignore Symptoms: If you feel a lump or notice changes in your breast, regardless of a recent mammogram, follow up with your doctor. Imaging is one tool, but it’s not a substitute for knowing your body.
When to Seek a Second Opinion
If your symptoms persist but your mammogram is clear, don’t hesitate to ask for a second opinion or request further testing. No test is perfect, and advocating for yourself is essential. Radiologists and breast health specialists understand this—and a good provider will support thorough investigation rather than dismiss concerns.
For trusted, professional care, consider booking your mammogram with Bergman Ross. Our experienced team uses advanced imaging technology and takes a patient-first approach to ensure clarity, accuracy, and peace of mind. Whether it’s your first scan or a follow-up, you’re in capable hands.