Have Dense Breasts? Here’s What to Do Next

Breast Cancer

28 Oct

Your breast screening letter says no sign of cancer. And then a friend asks whether anyone ever told you if your breasts are dense.

So you go back and find the letter. Maybe there it is — a line you skimmed straight past. Maybe it says category C, and nothing at all about what to do with that. Or maybe it isn't there at all, anywhere. And now you're wondering why. Was anything missed?

Most women hear "dense" and assume something has been found. Nothing has. Density describes the tissue itself, and what it changes is how well the mammogram can see your breast tissue. What you do about it depends on things that are specific to you.

I'm a breast surgeon and menopause specialist in Wellington. I see women after their mammograms, and this is a conversation I have every single day. So this is where to find your density, what C and D change, what extra scans find and what they cost you, what's different here in New Zealand, and what I actually recommend in my clinic.

Watch the video

Have Dense Breasts? Here's What to Do Next

This post is the written version of my video. If you'd rather watch, it's all there — the report, the trials, the New Zealand costs and what I do in clinic.

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Where to find it on your report

Dense breasts are one of two letters on your mammogram report: C or D. C is written as heterogeneously dense. D is extremely dense. Some clinics use software called Volpara, and then you might see a number or a grade instead of a letter.

You'd expect it to be on every mammogram report. It isn't. Whether you're told depends almost entirely on where you live.

Where you live changes this

United States. Since September 2024, every mammogram letter has to say whether your breasts are dense. It's a federal rule, so it applies in every state.
Canada. Most provinces now put it on the report.
Australia. For now it depends on your state. BreastScreen Australia has listed telling women their density among its first planned changes.
United Kingdom and New Zealand. On the free screening programmes, it usually isn't on your letter at all.

If you had your mammogram privately, look at the radiologist's report. Density is normally near the top, before the findings.

And if you can't find it anywhere, it's tempting to read that as good news. It might not be. It means nobody wrote it down for you.

It is entirely appropriate to ask.

What density actually is — what the breast is made of, how it's graded, and why dense tissue shows up white on a mammogram, the same white as a cancer — I've gone through with the mammogram pictures in my earlier video, Dense Breasts Explained. This post starts from the letter in your hand.

C or D: what it means for you

When women find that line, most of them assume they're unusual — that dense means something is wrong with their breasts. It doesn't. C and D together are about half of all women. In American data, about 4 in 10 women, or 40%, are density C, and about 1 in 10, or 10%, are density D (DenseBreast-info.org). We don't yet know the split for New Zealand women, because it hasn't been reported.

Density C means heterogeneously dense. Small things can hide in it. It's the biggest group of women who get told they have dense breasts, and for most of them, what happens next depends on their family history, their medical history, and whether or not they're on HRT. Not on the letter on its own.

Density D means extremely dense. This is where the mammogram is hardest to read. And it's also where the evidence for an extra scan is strongest.

Your letter isn't fixed, either. Density usually comes down with age and after menopause, and it can go up on HRT. If that's you, I've written about it in HRT Made My Breasts Dense — Do I Need to Stop Taking It?

Two separate things, joined together

Dense breasts mean two separate things, and they nearly always arrive together.

The first is about the picture

In a dense breast, the mammogram misses more. Dense tissue shows up white, and so does a cancer — so the radiologist is looking for white on white. It's like trying to spot a snowball in a snowstorm.

A screening mammogram picks up something like 70–80% of cancers overall. In extremely dense breasts, density D, that drops closer to half. The exact figure varies between studies and with the type of mammogram.

The second is about your risk

Women with extremely dense breasts — density D — are about twice as likely to develop breast cancer as women with average density, which is B (DenseBreast-info.org). For C, the increase is much smaller.

Twice sounds like a lot. Twice of what? In New Zealand, about 1 in 10 women will be diagnosed with breast cancer in her lifetime (Breast Cancer Foundation NZ), and that number already includes every density, A to D, as well as women with a strong family history. So doubling your own baseline is not the same as being likely to get it.

Most women with dense breasts never get breast cancer. And if you do get breast cancer, having dense breasts doesn't make it a more dangerous breast cancer.

What puts you in a high-risk group is density together with everything else: your family history, a gene change like BRCA, a previous biopsy that showed atypical cells, or radiotherapy to your chest when you were young.

Density changes how well the mammogram can see your breast tissue. On its own, it doesn't make you high risk.

Extra scans: what they find, and what they cost you

If the mammogram can't see well, the obvious answer is a better scan. That's roughly right — but it comes with a catch.

Extra imaging, sometimes called supplemental screening, means a second test after a normal mammogram: an ultrasound, an MRI, or a contrast mammogram.

The DENSE trial

The best evidence we have so far comes from the Netherlands. Women aged 50 to 75 with extremely dense breasts — density D — and a normal mammogram were offered an MRI. In that group, the cancers that turned up between screening rounds, the ones the mammogram had missed, fell from 5 in every 1,000 women to 2.5 in every 1,000 (Bakker et al, NEJM 2019). Only 59% of the women offered the MRI actually had it, so the effect in the women who did was larger.

So you'd think every woman with density D should have an MRI. But the MRI also found plenty that wasn't cancer. In the first round, about 8 in 100 women had a false alarm — called back for more tests or a biopsy for something that turned out to be fine. That's a lot of stress and anxiety for a lot of women.

The BRAID trial

Then there's a UK trial called BRAID, published in 2025. It included around 9,000 women with dense breasts and a normal mammogram. For every 1,000 women scanned, a contrast mammogram found 19 extra cancers, an abbreviated MRI 17, and an ultrasound 4 (Gilbert et al, Lancet 2025). These are early results from the first round.

What we don't know yet, from either trial, is whether finding these cancers earlier means fewer women will die of breast cancer. That's the question the trials still have to answer.

So two things to take from that. MRI and contrast mammogram find the most, and ultrasound finds fewer — which is why we don't use ultrasound as part of screening for women with dense breasts in New Zealand. And every extra scan finds things that turn out to be nothing, which means more appointments and, for some women, biopsies.

Could an MRI replace your mammogram? No. Some early changes, like DCIS, show up as tiny specks of calcium that an MRI or an ultrasound can miss. So extra scans go on top of a mammogram, not instead of it.

Where you live changes this

In the United States, the American College of Radiology recommends MRI for women with dense breasts who want extra screening, but the US Preventive Services Task Force says the evidence isn't strong enough yet to recommend extra scans for everyone. Insurance cover depends on the state you live in.

In New Zealand, extra scans aren't offered routinely, and health insurance doesn't cover an MRI when it's done for screening.

A clear result covers you for that day

A normal mammogram is an answer about your breasts on the day it was taken. If you notice something new afterwards, it needs looking at — whatever the letter said, and whatever your density.

What to look for:

a new lump or thickening that's still there after your period
skin that's dimpled or puckered
a nipple that's newly pulled in
blood-stained discharge from one nipple
redness or swelling that isn't settling

None of these is an emergency, and you don't need to go to the emergency department. But they're a GP appointment in the next week — not something to leave until your next scan in one, two or three years' time.

When you ring, say:

"I had a normal mammogram in March, I've been told my breasts are dense, and I've found a new lump."

Put in your own month. That tells your doctor you need an examination and a diagnostic scan, not another screening one. A diagnostic scan is for when you have a lump or a symptom. A screening scan is for when you don't have any breast problems.

And you'll be tempted to talk yourself out of it. I've only just been checked. You were checked for that day. If something's changed since then, it needs looking at again — and nobody is going to think you're wasting their time.

If you're in New Zealand

All of this assumes someone has told you that you have dense breasts. In New Zealand, on the free breast screening programme, nobody will.

In New Zealand

BreastScreen Aotearoa doesn't currently measure your breast density or tell you what it is. Its guidelines don't require density to be recorded, or for women to be told.

That may change. Health New Zealand has been reviewing it, and says it's working out what it would take — the staff, the scanning capacity, and somewhere for women to go next once they're told they have dense breasts. There's no date. The College of Radiologists recommended in 2024 that density be reported for every woman, and Australia is moving to tell women nationally. I think it will change here too. I'm not sure when.

In the meantime, the free programme is a 2D mammogram every two years from age 45, and it's being extended to 74 — phased in by the end of 2029 (Health New Zealand). If you have a strong family history or a gene change, your GP should refer you for extra screening outside the programme.

If you want to know your density, the route in New Zealand right now is a private mammogram. The radiologist's report will usually say what your density is, near the top. Extra scans are in the private sector, and you pay for them unless you're in a high-risk group. 3D mammogram, contrast mammogram and MRI are all available privately.

What it costs privately

Costs vary around the country, so treat these as a guide:

3D mammogram (also called tomosynthesis): about $450–$500.
Contrast mammogram: about $200 more than a 3D mammogram. It's only available in a small number of places so far, like Wellington.
Abbreviated MRI: about $1,000, offered by some private centres, including in Christchurch and Auckland.
Standard breast MRI: about $2,500.

What I recommend in my clinic

So what do I actually do in clinic? This is my own practice, and other specialists may do it a bit differently. It comes down to three things: your breast density, whether you're still having periods or are on HRT, and your family history.

Family history comes first, because it overrides everything else. If you're in a high-risk group — a gene change like BRCA, or a family history strong enough to put you at high risk on a risk calculator — I recommend a mammogram and an MRI every year, whatever your density.

If you're not in that group:

Density C, still having periods, or through menopause but on HRT: a 3D mammogram every year.
Density C, over 60 and not on HRT: a contrast mammogram. It includes an ordinary mammogram, so it's one appointment, not two.
Density D, still having periods or on HRT: an MRI on top of your mammogram is what serves you best. If you can afford it, maybe once every two or three years.
Density D, over 60 and not on HRT: a contrast mammogram every two years is a great option.

None of this is a medical emergency. You have time to find out, and time to decide.

What to look for, and what to ask

Go back to that letter, or to the report. Look for one line: C or D, or the words heterogeneously dense or extremely dense. That line is the thing I most want you to find. Write it down.

If it says C or D — or it isn't there at all — take three questions to your GP:

"What is my density category?"

"Putting that together with my family history, what is my overall risk — and is it high enough that an extra scan makes sense for me?"

"If it is, which test, how often, what will it cost — and what happens if it finds something that turns out not to be cancer?"

Sometimes your GP won't be able to answer all of that, and they might refer you to see a breast specialist. That's normal, and it's a good next step.

You have time. Ask the question. Then make the decision yourself.

The video