Should We Treat DCIS?
"I am frustrated with DCIS. Not with the women who have it — never that. I am frustrated with the way we talk about it, the way we name it, and in some cases, the way we treat it. Because the evidence tells a more complicated story than the treatment protocols often reflect."
Most women diagnosed with DCIS are told they need treatment — surgery, often followed by radiation, sometimes followed by years of endocrine therapy. And for many women, that is entirely the right recommendation.
But here is what often goes unsaid: not all DCIS behaves the same way. The grade of your DCIS — low, intermediate, or high — changes the biological story so significantly that the same three-letter diagnosis can mean two very different clinical situations. And the question of whether all DCIS requires immediate intervention is one of the most actively debated questions in breast surgery right now.
This post is not an argument against treatment. It is an argument for precision — for understanding what the evidence actually shows, and for asking the right questions before you decide.
The Problem with the Name
DCIS stands for ductal carcinoma in situ. Carcinoma is in the name — and that word carries enormous psychological weight. It says cancer. It activates every alarm in the body.
But "in situ" means something important: in place. The cells have not left the duct. They have not invaded the surrounding breast tissue. They have not entered the lymphatic system or the bloodstream. By the strict biological definition of cancer — a disease characterised by invasion and the ability to spread — DCIS is not yet there.
This does not mean DCIS is nothing. Some DCIS will progress to invasive breast cancer if left untreated. The question — and it is a genuinely difficult one — is which DCIS, in which women, over what timeframe.
THE CENTRAL PROBLEM
We treat all DCIS because we cannot yet reliably tell which cases will progress and which will not. That means some women receive treatment — with real side effects and real costs — for a condition that may never have harmed them. This is the overtreatment problem, and it is not a fringe concern. It is the subject of multiple large international clinical trials.
Grade — The Single Most Important Variable
If there is one thing to understand about DCIS, it is this: grade changes everything. Grade describes how abnormal the cells look under the microscope — how far they have drifted from normal breast duct cells — and it is the strongest predictor of biological behaviour we have.
These are untreated invasion risk figures — meaning the risk if no surgery were performed. For low-grade DCIS, a 9% invasion risk over ten years means that 91 out of 100 women with untreated low-grade DCIS would not develop invasive cancer in that period. And because the progression timeline is so extended, the question becomes: would that progression occur within a woman's expected lifespan at all?
For high-grade DCIS, the picture is different. A 36% ten-year invasion risk, with half of those progressions occurring within five years, makes a much stronger biological case for prompt surgical intervention.
The grade of your DCIS is not a detail — it is the foundation of the entire treatment conversation. If your surgeon has not discussed grade with you, ask directly: what grade is my DCIS?
The Mortality Question — The Number That Changes Everything
Here is a figure that rarely makes it into the first surgical appointment: the ten-year breast cancer-specific survival rate for DCIS exceeds 98%.
This is not a reason to dismiss the diagnosis. It is context that must sit alongside every treatment discussion. When the baseline mortality risk is already this low, the question of whether a given treatment meaningfully reduces it further — and at what cost in side effects and quality of life — becomes important.
>99%
Ten-year breast cancer-specific survival for DCIS — regardless of whether treatment is lumpectomy, mastectomy, or in selected cases, active surveillance. Long-term outcomes are equivalent across surgical approaches.
What this tells us: we are very good at treating DCIS. What it also tells us: the disease itself, even without optimal treatment, rarely kills within ten years. That context matters when weighing the burden of treatment against its benefit.
The Van Nuys Prognostic Index — A Framework for Decision-Making
Most breast surgeons in New Zealand and Australia use a tool called the Van Nuys Prognostic Index (VNPI) to help guide treatment recommendations. Developed by Melvin Silverstein at the University of Southern California and updated in 2003, it combines four variables — tumour size, margin width, nuclear grade with or without comedo necrosis, and patient age — each scored 1 to 3, giving a total range of 4 to 12.
In New Zealand and Australia, the VNPI is used in over 70% of DCIS cases — compared to less than 16% in the UK, where clinicians tend to rely more on individual clinical judgement. Asking your surgeon for your VNPI score is entirely appropriate. It is a useful framework for structuring the conversation — though it is not a fixed formula, and it does not incorporate biological markers such as hormone receptor status that we now know carry prognostic significance.
🇳🇿🇦🇺 Ask your surgeon directly: "What is my VNPI score, and how is it influencing your recommendation?" If they are not using the VNPI, ask what framework they are using to weigh size, grade, margins, and age — and how each is factoring into their advice.
Active Surveillance — What the Evidence Shows
For decades, the standard approach to DCIS has been surgery — lumpectomy or mastectomy — for virtually all cases. But a growing body of evidence is challenging whether this is necessary for all grades and presentations, and several large clinical trials are now directly testing active surveillance as an alternative for carefully selected low-risk DCIS.
THE COMET TRIAL
COMET TRIAL (COMPARISON OF OPERATIVE VS MONITORING AND ENDOCRINE THERAPY)
The largest active surveillance trial for DCIS to date. Enrolled women aged 40 and over with low or intermediate grade, hormone receptor-positive DCIS. Participants were randomised to either standard guideline-recommended surgery (lumpectomy ± radiation) or active surveillance with endocrine therapy (tamoxifen or an aromatase inhibitor) and regular monitoring. Two-year data published in 2024 showed no significant difference in invasive cancer-free survival between the two groups. The trial is ongoing — longer follow-up is needed before active surveillance can be considered standard practice, but the early data is encouraging and has not shown the harm that some predicted.
THE LORIS AND LORD TRIALS
LORIS (UK) AND LORD (NETHERLANDS/BELGIUM) TRIALS
Two European trials similarly testing active surveillance for low-grade DCIS in selected patients. Both are ongoing. Preliminary data has not shown alarming rates of progression in the surveillance arms, reinforcing the signal from COMET that active surveillance for carefully selected low-grade DCIS may be a safe option — though the evidence base is not yet mature enough to make this a routine recommendation outside clinical trial settings.
WHAT THIS MEANS RIGHT NOW
Active surveillance for DCIS is not yet standard practice outside clinical trials. The evidence is promising but incomplete. What it does mean is that if you have low or intermediate grade DCIS, it is entirely reasonable to ask your surgeon whether active surveillance has been considered for your case — and if not, why not. You are not asking an unreasonable question. You are asking a question that is being asked at the highest levels of international breast surgery.
🇳🇿🇦🇺 Active surveillance trials are not currently running in New Zealand or Australia. If you are interested in this approach and you have low-grade DCIS, ask your surgeon whether there are any clinical trial enrolment pathways or whether your case might be managed under a watchful waiting protocol at a centre with relevant expertise.
The Overtreatment Problem — Naming It Honestly
The rise of mammographic screening has dramatically increased DCIS detection. In New Zealand, 350 to 500 women are diagnosed with DCIS every year — the vast majority through BreastScreen Aotearoa. Most of these cases were not causing any symptoms. They were found because we looked.
This is both a success of screening and a clinical challenge. We are finding more DCIS than we would ever have found before mammography — and we are treating most of it. But the mortality rate from DCIS has not fallen in proportion to the dramatic rise in cases detected and treated. That is the signal that makes researchers ask: are some of the cases we are finding and treating ones that would never have harmed the woman in her lifetime?
The honest answer is: almost certainly yes, for a proportion of low-grade cases. We do not yet have a reliable way to identify which specific women those are — which is why surgery remains the standard recommendation. But it is the scientific reason that active surveillance trials are being run, and it is the reason this conversation belongs in every DCIS clinic.
WHAT I AM NOT SAYING
I am not saying DCIS should not be treated. For high-grade disease, for younger women, for larger lesions with involved margins, the case for prompt treatment is strong and the recommendation is clear. What I am saying is that the treatment conversation — particularly for low and intermediate grade DCIS — should be genuinely individualised, evidence-based, and inclusive of the full picture. That includes the absolute numbers, the overtreatment signal, and the emerging trial data on active surveillance.
Questions to Ask Before You Decide
Wherever you are in this process — at your first surgical appointment or reconsidering a recommendation — these are the questions that will make the conversation more honest and more useful.
What to Take From This
DCIS is real. In some cases it is a genuine precursor to invasive breast cancer, and treatment is warranted and important. But the diagnosis is not uniform — and neither should the treatment be.
Grade matters. The absolute numbers matter. The overtreatment signal is real and is being taken seriously at the highest levels of breast surgery research. And the question of whether your specific DCIS requires immediate intervention — or whether carefully monitored surveillance might be an appropriate conversation — is not a fringe idea. It is the subject of multiple large international clinical trials.
What I want you to leave with is not anxiety, and not complacency. I want you to leave with precision — the ability to ask the right questions, understand the actual numbers, and make a decision that is genuinely yours.