Among women with low-risk ductal carcinoma in situ, the incidence of invasive cancer in the same breast does not appear to be different between those who have undergone active monitoring and those who have received a surgical procedure, according to the results of COMET trial.

In the intention-to-treat analysis, the 2-year cumulative risk of ipsilateral invasive cancer was 4.2 percent in the active monitoring arm vs 5.9 percent in the guideline-concordant care arm (surgery with or without radiation therapy). The difference of ?1.7 percent (upper limit of the 95 percent confidence interval [CI], 0.95) established the noninferiority of active monitoring to guideline-concordant care. [JAMA 2024;doi:10.1001/jama.2024.26698]

Likewise, the invasive tumour characteristics did not significantly differ between patients in the active monitoring and guideline-concordant care arms. These included the size and number of the largest target lesion (p=0.33 and p=0.29, respectively), estrogen and progesterone receptor status (p=0.51 and p=0.09, respectively), and highest invasive cancer grade (p=0.34), among others.

Similar results were obtained in the per-protocol analysis. The 2-year cumulative rate of ipsilateral invasive cancer was 3.1 percent (95 percent CI, 2.31?6.00) with active monitoring vs 8.7 percent (95 percent CI, 5.06?12.21) with guideline-concordant care (difference, ?5.6 percent; upper limit of the 95 percent CI, ?2.07).

“The findings are novel, as all current treatments for DCIS require surgical excision, despite a growing body of evidence that supports that not all DCIS is destined to progress to invasive cancer,” the authors said.

“For women with a low risk of invasive progression, guideline-concordant care may offer little clinical benefit, resulting in potential for overtreatment… However, omission of surgery for DCIS remains a highly controversial challenge to dogma, with both patients and clinicians fearing that the absence of excision might result in an unacceptably high rate of invasive cancer,” they added.

The data from COMET may help patients and their clinicians make informed decisions about DCIS treatment, according to lead author Dr E Shelley Hwang from Duke University in Durham, North Carolina, US, who presented the results at SABCS 2024.

“Our findings are reassuring, and longer-term follow-up will have important implications for the future inclusion of active monitoring as a treatment option for low-risk DCIS,” Hwang said.

In COMET, the intention-to-treat population included 957 women (75.0 percent White) at least 40 years of age with a new diagnosis of hormone receptor?positive grade 1 or grade 2 DCIS without invasive cancer. These women were randomly assigned to undergo active monitoring (n=484, median age 63.7 years) or guideline-concordant care (n=473, median age 63.6 years). The per-protocol population comprised 673 patients who received their assigned treatment.

“Longer follow-up will help determine whether active monitoring offers durable safety and acceptability for patients in the management of this low-risk disease,” Hwang and colleagues said.