Ductal Carcinoma In Situ (DCIS) is not cancer, yet it is often described as the earliest form of breast cancer: Stage 0. It’s when abnormal cells are found in the milk ducts but haven’t yet invaded outside the ductal space and spread to the surrounding breast tissue.
DCIS was rarely diagnosed prior to mammography. Now, over 50,000 women in the U.S. are diagnosed with DCIS each year, almost exclusively through routine mammograms. While DCIS itself is not life-threatening, the concern is that it could progress to invasive breast cancer in some women.
The challenge? We don’t always know which cases of DCIS will progress to become cancer and then which will become lethal metastatic breast cancer, and which won’t.
Historically, DCIS has been treated aggressively with surgery, radiation, and sometimes hormone therapy, similar to locally invasive breast cancer. But many experts and patients have questioned whether such intense treatment is always necessary. Could it be that women with asymptomatic DCIS are being overtreated? And what happens if we take a less aggressive approach?
NBCC has long questioned the current one-size-fits-all aggressive approach to treating DCIS and called for high quality evidence from randomized trials to guide less invasive approaches for appropriate patients.
The COMET trial (“Comparison of Operative versus Monitoring and Endocrine Therapy”) is one of the first major studies to tackle this question head-on in a low-risk DCIS population.
The COMET trial tested two different approaches for managing low-risk DCIS. In this study, low risk was defined as DCIS that is low or intermediate-grade, hormone receptor-positive, HER2-negative, with no signs of invasive cancer, and at least two pathologists had to agree on the diagnosis. Only women aged 40 years or older who had their DCIS detected through a screening mammogram were eligible to participate. Participants were randomly assigned to one of the following management approaches:
These results were presented for the first time at the 2024 San Antonio Breast Cancer Symposium on December 12, 2024, and were simultaneously published in JAMA. The research was also supported by a team of advocates who participated in the study design, trial monitoring, and reporting.
The trial followed 957 women with low-risk DCIS for 2 years. Here’s what they found:
The higher rate of invasive breast cancer in the guideline-concordant care group is likely due to upstaging of the DCIS at the time of surgery to invasive breast cancer. Though not common, some cases of DCIS may actually harbor small amounts of locally invasive cancer that are only detected after surgery and a more detailed pathological examination.
Interestingly, nearly 44% of women randomized to the guideline-concordant care group chose to switch to active monitoring instead of proceeding with surgery. In contrast, a much smaller percentage (14%) of individuals in the active monitoring group chose to switch to surgery. The investigators anticipated that some participants might want to switch between treatment options and accounted for this in their statistical analysis plan. This flexibility reflects the importance of patient preference and shared decision-making in managing DCIS.
In simpler terms, for women with low-risk DCIS, choosing to monitor the condition instead of rushing into surgery did not lead to a higher risk of invasive breast cancer in the short term.
The COMET trial gives us the first real evidence that we don’t need a “one-size-fits-all” approach to treating DCIS. Not every case of DCIS will turn into invasive cancer, and of those that will, not every case will progress to lethal metastatic disease, and not every woman may need surgery right away, or at all.
This doesn’t mean that active monitoring is right for everyone. Some women may prefer the peace of mind that comes with surgery. Others may want to avoid aggressive treatment unless it becomes absolutely necessary. What’s most important is that patients and their doctors now have evidence to support a choice that aligns with their values and priorities.
While the COMET trial results are exciting, the study followed women for only 2 years. Longer-term follow-up is still needed to confirm that active monitoring remains safe over 5, 7, or even 10 years. Additional studies, like the LORD and LORETTA trials, are also underway and will add to what we know about managing low-risk DCIS.
In the meantime, the COMET trial is a major step toward smarter, more patient-centered care. It challenges us to rethink the way we treat DCIS and to focus on strategies that may be considered “standard of care” but do not benefit women.
