Patients with low-risk ductal carcinoma in situ (DCIS) are unlikely to experience recurrence following breast conservation surgery, but radiation therapy can reduce that small risk even further.

New findings at the American Society for Radiation Oncology (ASTRO) 2018 showed that whole-breast radiation therapy (WBRT) reduced recurrence by half compared to observation. The reduction in recurrence rate was much larger than the study authors had anticipated.

"The larger than expected reduction has yielded meaningful results in spite of the accrual ," explained lead author Beryl McCormick, MD, chief of the External Beam Radiotherapy Service at Memorial Sloan Kettering Cancer Center and professor of radiation oncology at Cornell University in New York City

The study included 629 patients, with a medium follow-up of 12.4 years. The cumulative incidence of local recurrence was 2.8% in the WBRT arm vs 11.4% in the observation arm (hazard ratio [HR], 0.26,  = .0001). The cumulative incidence of invasive local recurrence was 1.5% in the WBRT arm vs. 5.8 for the conservation arm (HR, 0.34,  = 016).

"Findings should inform meaningful patient-doctor discussions about risks, benefits, and the patient's degree of comfort – which varies greatly – about local control with or without radiation ," said McCormick.

DCIS is considered to be a preinvasive or precancerous lesion that does not metastasize to other parts of the body. Before the advent of screening mammography , DCIS was rarely diagnosed. There has been discussion as to how aggressively DCIS should be treated.

A recent study using data from the SEER database from 1998 to 2014 found that lumpectomy plus radiation therapy was associated with a statistically significant reduction in risk for breast cancer-related death with either lumpectomy or mastectomy alone in women with DCIS. However, the clinical benefit is small, and routine radiation therapy is not advised.

Good Risk Disease Can Benefit

Although DCIS is generally noninvasive, it has been unclear which cases are most likely to progress. "DCIS used to be considered one entity, and we were convinced that DCIS is not all alike," said McCormick. "And we were the first to define 'good risk' and 'high risk,'" she said.

In this study, the authors evaluated the impact of WBRT in comparison with observation in women with good-risk DCIS following breast conservation surgery . For this trial, good-risk DCIS was defined as clinically occult DCIS that was detected either through mammography or incidentally. Furthermore, the tumor had to be 2.5 cm or smaller; margins had to be 3 mm or less, and the tumor had to be of low or intermediate nuclear grade.