The management of ductal carcinoma in situ (DCIS) is entering a period of increasing treatment de-escalation. Historically, DCIS has largely been managed with surgical excision, followed in selected patients by radiation therapy and/or endocrine therapy.

But growing recognition of the biological heterogeneity of DCIS — coupled with prospective clinical trial data — is challenging the assumption that all patients require immediate surgery.

The emerging question is not whether DCIS carries a risk of progression to invasive breast cancer. It does. Rather, it is whether clinicians can reliably identify a subset of patients whose short-term risk is sufficiently low to permit active monitoring while reserving intervention for evidence of progression.

“Previously, all DCIS was treated the same and the presumption was that it progressed to invasive cancer,” says Anastasia Tousimis, M.D., breast surgical oncologist, deputy director of Baptist Health Cancer Care and chief of breast surgery at Baptist Health Cancer Care. “Research has shown that it is not all the same and some low-risk DCIS does not progress.”

COMET Adds Prospective Evidence to the De-Escalation Discussion

The randomized COMET trial has provided some of the most consequential prospective evidence supporting this discussion. The study compared guideline-concordant care — surgery with or without radiation — with active monitoring in women age 40 and older with hormone receptor-positive, grade 1 or 2 DCIS without invasive disease.

Among 957 participants included in the primary analysis, the two-year cumulative rate of ipsilateral invasive cancer was 4.2 percent in the active-monitoring group compared with 5.9 percent in the guideline-concordant care group, meeting the trial's prespecified criterion for noninferiority.

Those findings are provocative but require appropriate context. Median follow-up was approximately three years, and the COMET investigators explicitly noted that additional invasive events are expected with longer follow-up. Analyses at five, seven and 10 years are planned.

For clinicians, therefore, the current evidence does not support abandoning established DCIS treatment paradigms broadly. It does, however, strengthen the rationale for risk-adapted management and shared decision-making in appropriately selected patients.

“Most cases will not become life-threatening and should not be overtreated,” Dr. Tousimis says. “By identifying low-risk DCIS, we can offer active monitoring and de-escalate care.”

Defining ‘Low Risk’ Remains the Central Challenge

DCIS encompasses a biologically heterogeneous group of preinvasive lesions. That heterogeneity makes risk stratification central to any active-monitoring strategy.

“The pathologic factors we use to stratify risk include nuclear grade, hormone status and the absence of invasive disease,” Dr. Tousimis explains. “The clinical factors include age, whether DCIS was diagnosed on screening mammogram without evidence of a palpable mass and localized disease.”

The distinction is critical because active monitoring is not intended to substitute for surgery across the DCIS spectrum. The COMET population, for example, was restricted to hormone receptor-positive, grade 1 or 2 disease without invasive cancer.

Imaging phenotype and disease distribution provide additional information when considering surveillance.

Gladys Giron, M.D., a breast surgical oncologist at Baptist Health Miami Cancer Institute, notes that DCIS is seldom diagnosed as a palpable mass and is typically detected through screening or diagnostic mammography.

“Imaging can identify patients suitable for active monitoring, including those with one area of DCIS and fatty breast tissue favorable for mammographic monitoring,” Dr. Giron says.

Conversely, extensive DCIS relative to breast size, multiple areas separated by normal tissue or disease involving different quadrants can make active monitoring inappropriate. Histologic grade, estrogen receptor status and, increasingly, molecular testing can further inform risk assessment.

Surveillance Requires a Defined Escalation Pathway

Active monitoring is not synonymous with passive observation. It requires structured surveillance and predefined triggers for diagnostic escalation.

In COMET, diagnostic mammography was required every six months for the affected breast and annually for the contralateral breast. New clinical or imaging abnormalities — including a new mass, architectural distortion or increasing calcifications — could trigger core needle biopsy.

That closely parallels how Dr. Giron describes surveillance in clinical practice.

“Typically, the patient will have a mammogram of the breast with DCIS every six months,” she says. “An increase in the number of microcalcifications, new suspicious microcalcifications, or the development of a suspicious mass or distortion would prompt additional testing and discussion of surgical treatment and radiation.”

The limitation, of course, is that mammographic stability is not equivalent to biological certainty.

“Mammography is the gold standard study for detection and subsequent follow-up or active surveillance of DCIS,” Dr. Giron says. “It cannot predict which patients are more likely to experience progression of DCIS itself or progression to invasive disease.”

This underscores one of the central unresolved issues in DCIS management: improving discrimination between lesions likely to remain indolent and those with clinically meaningful invasive potential.

Surgery Remains Integral — But Timing May Become More Individualized

Surgical excision remains a cornerstone of DCIS management and provides both local control and complete pathologic assessment. The active-monitoring paradigm, however, raises the possibility that timing of surgery may become more individualized for a carefully defined low-risk population.

This requires nuanced counseling, particularly because the term “carcinoma” can create a strong expectation for immediate intervention.

“It is important as clinicians that we explain to patients that DCIS is not an invasive cancer which would harm them, but contained cancer cells which have not spread,” Dr. Tousimis says. “Most patients are reassured that they will be followed closely and not need an invasive surgery.”

For specialists, that discussion should also include what is not yet known: the durability of short-term active-monitoring outcomes, the possibility of occult invasive disease at diagnosis and the need for subsequent intervention if clinical, radiographic or pathologic findings change.

Radiation Decisions Are Also Becoming More Risk-Adapted

De-escalation in DCIS is not limited to surgery. Radiation oncologists have long faced a related question after breast-conserving surgery: Which patients derive sufficient absolute benefit from adjuvant radiation to warrant treatment?

“Patients undergoing lumpectomy for DCIS are recommended to have a discussion with an expert radiation oncologist in order to discuss the risk-benefit ratio of adjuvant radiation therapy,” says Youssef Zeidan, M.D., radiation oncologist at Eugene M. & Christine E. Lynn Cancer Institute at Boca Raton Regional Hospital, part of Baptist Health.

That discussion incorporates DCIS size and grade, margin status, patient age, hormone-receptor status and willingness to receive endocrine therapy, among other considerations.

Active monitoring potentially shifts the radiation decision further downstream. For patients who defer surgery, radiation is likewise deferred, but it remains available should subsequent disease evolution warrant local therapy.

“Early results from randomized trials suggest that a subgroup of patients might be eligible for an active monitoring approach; however, the follow-up remains short,” Dr. Zeidan says. “For patients choosing active monitoring, the decision for radiation therapy is deferred rather than declined forever.”

Biomarkers May Further Refine DCIS Management

The next phase of DCIS de-escalation is likely to depend on improving risk stratification beyond conventional clinical, radiographic and histopathologic variables.

Molecular assays are already being investigated as tools to estimate recurrence risk and potential benefit from radiation. Their ultimate role may be particularly relevant in the intermediate clinical scenarios where traditional variables do not produce a clear treatment recommendation.

“There is no one size that fits all for management of DCIS,” Dr. Zeidan says. “Molecular tests for DCIS continue to prove helpful for risk stratification and estimation of the benefit of adjuvant radiation therapy.”

According to Dr. Zeidan, the NRG-CC0116 clinical trial is anticipated to open across Baptist Health Cancer Care centers and will evaluate whether the DCISionRT biosignature test can help guide adjuvant radiation therapy decisions for DCIS.

Moving From Uniform Treatment Toward Risk-Adapted Care

The emerging active-monitoring literature does not resolve the DCIS treatment debate. It reframes it.

The COMET findings provide randomized evidence that, over the short term, carefully selected patients with low-risk DCIS undergoing active monitoring did not experience a higher rate of ipsilateral invasive cancer than patients assigned to guideline-concordant care. Longer follow-up will be essential before clinicians can determine whether that relationship persists over time.

For multidisciplinary breast cancer teams, the immediate implication may be less about replacing surgery than expanding the quality of the conversation surrounding it.

Patient age, imaging characteristics, extent of disease, grade, hormone-receptor status, pathology, molecular information, comorbidities and patient preferences can all contribute to a more individualized assessment. Active monitoring also requires patients who understand the uncertainties and are willing and able to adhere to longitudinal surveillance.

“Ongoing surveillance is important in expanding our knowledge so we may more accurately determine which patients can be safely monitored,” Dr. Giron says. “This continued imaging will allow early detection of changes that could indicate worsening of the DCIS.”

For cancer specialists, the evolving paradigm represents a familiar direction in precision oncology: moving away from treating a diagnostic label uniformly and toward matching the intensity and timing of therapy to the biology and clinical risk of the individual disease.