"DCIS is the diagnosis that keeps me up at night. Not because it's the most dangerous thing I treat — it isn't. But because I'm often sitting across from a woman who has been told she has cancer, and I genuinely cannot tell her with certainty whether treating it will change her outcome."
If you've been diagnosed with DCIS, you've probably already had a surgical consultation where treatment was presented as the obvious next step — surgery, likely followed by radiation, possibly hormone therapy. And somewhere in that conversation, or in the Googling that followed, a question formed that you might not have felt comfortable asking out loud.
Do I really need all of this?
It is a legitimate question. And it deserves a legitimate answer — not reassurance, not a protocol, but an honest look at what the evidence actually shows.
This is that answer.
Why There Is No Simple Yes or No
Here is the fundamental problem. When DCIS is found on a mammogram — which is how most women receive this diagnosis — the ethical standard of care is to treat it. Which means our understanding of what DCIS would do if left completely alone is based on imperfect data: historical cases where the diagnosis was initially missed, or women who were considered too unwell for surgery.
Everything we know about DCIS progression comes with caveats. Wide confidence intervals. Small sample sizes. A bias toward lower-grade disease because high-grade DCIS is less commonly missed.
What we do know is this: without treatment, somewhere between 10 and 50 percent of DCIS cases would eventually progress to invasive breast cancer. That wide range is not sloppy science. It is an honest reflection of how much biological variability exists in this disease.
The flip side of that number — the part that does not get said enough — is that the majority of DCIS would never have become invasive cancer in that woman's lifetime. And right now, we cannot reliably tell, from any test we currently have, which category yours falls into.
The treatment conversation for DCIS should not be a single standard protocol. It should be a genuine, individualised discussion that starts with your specific grade, size, age, and values. Anyone who gives you a simple yes or no without that discussion is not giving you the full picture.
Why Grade Changes Everything
Not all DCIS is the same. And the single most important variable in this conversation is grade — how abnormal the cells look under the microscope, and how fast they are likely to grow.
Low Grade DCIS (Grade 1)
Low-grade DCIS tends to grow slowly. The cells look mildly abnormal. They are generally oestrogen-driven. Studies suggest that low-grade DCIS can take decades to progress — or may never progress at all.
That 61% overdiagnosis estimate is significant. It means that for the majority of women with low-grade DCIS found on screening, the diagnosis may never have caused clinical harm within their lifetime. This is the number that sits at the heart of why the active surveillance conversation is happening.
High Grade DCIS (Grade 3)
High-grade DCIS is a fundamentally different entity — and the conversation is genuinely not the same.
When high-grade DCIS progresses, it progresses into high-grade invasive cancer — which carries a significantly higher risk of distant metastasis than the invasive cancers that tend to arise from low-grade disease. The overdiagnosis argument is much weaker for high-grade DCIS, particularly in younger women.
There is also a biologically important point worth understanding. Low-grade and high-grade DCIS are not two points on a spectrum. They are distinct disease entities with different chromosomal alteration patterns and different evolutionary trajectories. Low-grade DCIS does not reliably evolve into high-grade DCIS. They follow separate pathways — which is exactly why they require different clinical conversations.
| LOW GRADE | Factor | HIGH GRADE |
|---|---|---|
| ~1% per year | Recurrence rate | ~2% per year |
| 9% at 10 years (untreated) | Invasion risk | 36% at 10 years (untreated) |
| ~61% (age-independent) | Overdiagnosis rate | 21–66% (age-dependent) |
| Potentially decades | Progression timeline | Faster — years not decades |
| Emerging evidence (COMET) | Active surveillance | Not currently supported |
The COMET Trial — The Best Evidence We Have
For the past decade, researchers have been trying to answer a very specific question: for women with low-risk DCIS, is it safe to manage without immediate surgery? Three trials were designed to answer this — LORIS in the UK, LORD in Europe, and COMET in the United States.
LORIS and LORD both closed early, before they could enrol enough women to give definitive answers. The reason is worth noting: women found it psychologically very difficult to accept a watch-and-wait approach when they had been told they had cancer. That tells us something important about how DCIS is communicated — and why the language we use around this diagnosis matters so much.
COMET is the trial that has given us the most useful data so far.
Surgery group
Active monitoring group
Randomised to surgery (guideline-concordant care) vs active monitoring with regular surveillance imaging. At two years, active monitoring did not result in a higher rate of invasive cancer than surgery. The lead investigator noted that two years is too short for a definitive conclusion — five-year data will be decisive. Not yet sufficient to change standard of care outside clinical trials, but the most encouraging signal yet that active surveillance may be safe for carefully selected women with low-grade DCIS.
What Good Shared Decision-Making Looks Like
A good treatment conversation for DCIS is not your surgeon explaining what is going to happen to you. It is a real discussion — one that starts with your specific grade, size, age, other health concerns, values, and preferences — and works outward from there.
Low-grade, small-volume, screen-detected DCIS with other health concerns. The risk of overtreatment — surgery, anaesthetic, radiation, and their side effects — may well outweigh the risk of careful monitoring. A surveillance conversation is clinically reasonable.
High-grade DCIS, extensive disease, decades of life ahead. The evidence supports treating this seriously and promptly. The risks of under-treatment are real. This is not the same conversation as low-grade disease.
Most women sit somewhere between those two poles — which is exactly why the conversation matters as much as the recommendation.
Questions to Ask Before You Decide Anything
Bring These to Your Next Appointment
You are not being difficult by asking these questions. You are doing exactly what informed consent requires of both of you.
High Grade DCIS — The Honest Answer
I want to be direct about this, because I don't want anything in this post to be misread.
The evidence does not currently support active surveillance. The progression risk is meaningfully higher. The consequences of progression are more serious. The overdiagnosis argument is significantly weaker — particularly if you are under 60. High-grade DCIS should be treated. That may change as more trial data emerges, but right now that is where the evidence sits.
If you have high-grade DCIS and you are hoping this post will tell you that you can avoid surgery, I understand that hope. But the honest answer — based on the evidence we currently have — is that for high-grade disease, treatment is the right recommendation.
The Honest Answer
Do you really need treatment for DCIS?
It depends. It depends on your grade. It depends on your size. It depends on your age and your individual circumstances. And it depends on a real, honest, properly-informed conversation that takes all of those things into account.
- If you have low or intermediate grade DCIS, it is completely reasonable to ask about the evidence for active surveillance. Not because surgery is wrong — it isn't, and it remains the standard of care — but because informed consent means understanding all your options.
- If you have high-grade DCIS, the current evidence supports treating it. You deserve an honest explanation of why, not just a protocol handed to you without discussion.
DCIS is not nothing. But it is also not a death sentence, and the treatment decision should not feel like one. You have time. Ask the questions. Push for the conversation.
DCIS is not a medical emergency. You have time to understand your diagnosis fully, seek a second opinion if you want one, and be part of the decision about what happens next. No decision needs to be made this week.
Continue Reading: The DCIS Series
🇳🇿🇦🇺 Note for New Zealand and Australian readers: hormone receptor (ER) testing is not routine for DCIS in NZ and Australia, and endocrine therapy is not standard practice here. Some statistics in this post reflect US and UK clinical practice where ER testing is routine. This is explained in the video above.
Book a consultation: mybreastcarecentre.co.nz