October is Breast Cancer Awareness Month. It's a chance to remind women across Aotearoa that finding breast cancer early saves lives, and to help them make informed decisions about their breast health. One important factor affecting how early breast cancer can be detected on a mammogram is breast density.
What is breast density?
Breast density describes how much glandular and connective tissue your breasts contain compared with fatty tissue, as seen on a mammogram.
Radiologists classify density into four categories using the American College of Radiology's BI-RADS® system. These range from almost entirely fatty (Category A) to extremely dense (Category D), as shown in the graphic below.
(Image: Breast Density Explained – Volpara Health)
The star in the images shows how cancer may be hidden on a mammogram. It illustrates why women with dense breasts may need additional imaging.
On a mammogram, dense breast tissue (BI-RADS Categories C and D) appears white, and so do cancers. This can make detection harder.
Two challenges for women with dense breasts
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Reduced diagnostic sensitivity: Mammograms are less effective at finding cancer in dense breasts, especially in Categories C and D.
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Increased cancer risk: Women with dense breasts have a 1.2–4 times higher risk of developing breast cancer than women with less dense tissue.
How supplementary imaging can help
At Bay Radiology, we offer a range of advanced breast imaging services designed to improve early detection and provide greater clarity, especially for those with Category C and D breast density.
Breast screening recommendations based on breast density
The following recommendations are for women aged 40 to 75, based on their breast density category.
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BI-RADS Category A and B |
Mammogram or tomosynthesis (a three-dimensional (3D) mammogram). |
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BI-RADS Category C |
Tomosynthesis. If you have extra risk factors (such as family history or personal history of breast cancer), consider adding:
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BI-RADS Category D |
Tomosynthesis and in addition:
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Risk assessment
Breast density should be evaluated in conjunction with other risk factors such as:
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Family history and genetics (e.g. BRCA mutations)
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Menstrual and reproductive history
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BMI and lifestyle factors (e.g. alcohol intake, smoking)
A comprehensive risk assessment helps guide decisions around the need for supplementary screening and frequency.
What you can do this October and beyond
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Ask about your breast density after your next private (non-BreastScreen) mammogram.
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Book a screening if you’re due - or overdue.
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Talk to us about the best imaging options for your individual risk profile.
Your breast health, our priority
At Bay Radiology, we're committed to expert breast imaging across New Zealand. Whether it's your first mammogram or you need advanced diagnostic imaging, we're here to support you every step of the way.