COMET (Comparison of Operative versus Monitoring and Endocrine Therapy)

Most ductal carcinoma in situ is treated with surgery and often radiotherapy although only a fraction would ever become invasive. COMET, run by the Alliance Foundation Trials group, was a pragmatic randomised non-inferiority trial of 997 women aged 40 or over with low-risk (grade 1 or 2, hormone receptor-positive, HER2-negative) DCIS, comparing active monitoring with mammography every six months, with endocrine therapy offered, against standard surgery with or without radiotherapy. The primary endpoint was the rate of ipsilateral invasive cancer at two years.

At two years the invasive cancer rate in the monitoring arm was not inferior to that in the surgery arm, and quality of life was similar. The follow-up is short and many monitored women's cancers were found at planned surgery, so longer results and the parallel LORD and LORIS trials are awaited, but COMET is the first randomised evidence that active monitoring of low-risk DCIS is safe in the short term.