Immediate treatment has long been standard for patients with ductal carcinoma in situ (DCIS), but confidence is building that some women don’t need surgery.

With the growing recognition that not all cases of DCIS will do harm, acceptance of active surveillance as an option for patients at low risk for invasive disease is growing, as well.

“We don’t have to subject everybody to surgery, drugs, or radiation,” said Alastair Thompson, MD, a breast cancer surgeon at the Baylor College of Medicine in Houston and an authority on the topic.

Several studies have been investigating active monitoring as an alternative to immediate treatment for women with low-risk DCIS — including the LORD trial in Netherlands, where participants were allowed to choose between those two options. Interim results, reported on March 27 at the European Breast Cancer Conference, were described as “reassuring,” showing that rates of invasive cancer around the 2-year mark were comparable in the active surveillance and standard-treatment groups.

Thompson was a senior investigator on the COMET trial, the only randomized trial to report outcomes so far. It found that active surveillance wasn’t inferior to upfront surgery at 2 years, with rates of progression to invasive breast cancer of 4.2% with surveillance and 5.9% with surgery, mostly due to surgical upstaging.

While the field awaits longer-term data, Thompson shared his thoughts with Medscape Medical News after his presentation on the topic at Miami Breast Cancer Conference 2026. The following interview has been edited for clarity and length.

Who is an appropriate candidate for active surveillance?

The evidence to date supports surveillance in women aged 40 years or older with grade 1 or 2, estrogen-receptor positive DCIS, and no palpable mass.

HER2 protein isn’t routinely tested in DCIS, but if it is and it’s positive, we want to exclude those patients because they have a higher chance of progression.

Calcifications on mammography don’t factor into my decision. There are many different forms, and some are probably less associated with invasive progression than others. What calcifications mean on mammograms will probably evolve over time.

Even if it’s a small risk for progression, some women want intervention immediately. Others — about 1 in 10 in my practice — don’t want surgery. If they meet the criteria, my colleagues and I are happy to monitor them.

What’s the risk of active surveillance in DCIS?

Evidence is coming in from different directions, but it’s probably on the order of a 10% risk of developing invasive cancer over 10 years.

When we monitor someone, we’re going to pick up changes very early, so it will be an invasive cancer of less worrisome features, meaning estrogen-receptor positive and node-negative.

For about 90% of women even a decade and more out, nothing changes. They haven’t needed surgery, and hopefully never will.

How do you do surveillance?

We use the COMET trial methodology of physical exams and mammograms every 6 months for the first 5 years, alternating imaging of the affected breast and both breasts. After that, we dial it back to annual imaging of both sides. If anything changes, we biopsy.

Trials in the UK and Netherlands [LORD] use annual imaging with physical exams. We are being very cautious in COMET during the first 5 years, when the risk for progression is highest, to make sure we pick up changes early on. Women seem fine with the 6-month approach. The added burden compared with annual follow-up is acceptable.

The role of endocrine therapy is unclear at the moment. Any reduction in risk is probably small, and it comes at the cost of side effects, which for some women are not inconsiderable.

If women are willing to try endocrine therapy, I’m happy to work with them on it. Others won’t even consider it, and I respect that. I can point to the fact that in Netherlands, women do not take endocrine therapy for DCIS, and their survival is just as good as in the rest of the world.

What do we still need to know?

I think there are three key questions. First, which women are truly good candidates for surveillance? Second, if invasive cancer develops, does it affect breast cancer-specific mortality? And third, is there an overall survival disadvantage to monitoring? It seems unlikely, but we don’t have overall survival data yet.

In the short term, we need longer follow-up from COMET. I’d like to see the 5-year analysis and also a deeper analysis of the effects of endocrine therapy in women who chose it. We still have quite a lot of information to pull out of COMET. The key thing is going to be the longer-term follow-up.

Thompson reported having no conflicts of interest.

M. Alexander Otto is a physician assistant with a master’s degree in medical science and a journalism degree from Newhouse. He is an award-winning medical journalist who worked for several major news outlets before joining Medscape. Otto is also an MIT Knight Science Journalism fellow. Email: aotto@mdedge.com.