Delaying radiation therapy too long after surgery significantly increases the risk of recurrent tumours in women treated for very early, or what is referred to as "stage 0," breast cancer, according to new research at Washington University School of Medicine in St. Louis.

Stage 0 breast cancer - or ductal carcinoma in situ (DCIS) - is diagnosed based on the presence of abnormal cells in the milk ducts of the breast.

Every year, more than 60,000 U.S. women are diagnosed with DCIS, and experts often debate how best to treat it because the abnormal cells don't always develop into full-blown, or invasive, breast cancer.

Standard therapies include lumpectomy, lumpectomy plus radiation, or total mastectomy.

The researchers found that women were much more likely to experience a recurrence of DCIS or higher-stage cancer in the same breast if they received radiation therapy eight or more weeks after a lumpectomy or did not receive radiation therapy after surgery.

The data was presented at the American Association for Cancer Research (AACR) Annual Meeting 2016 in New Orleans.

"This study indicates not only that radiation therapy is an important component in the treatment of DCIS but also that it must be received in a timely manner," said Ying Liu, MD, PhD, the study's lead author.

She is an instructor in surgery at the School of Medicine and a research member at Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine.

Delays in radiation therapy were more common among women who were black; unmarried; on Medicaid; diagnosed during the later years of the study; diagnosed with larger tumours; or whose cancer wasn't entirely removed during surgery.

"These groups, especially, may benefit from undergoing radiation therapy sooner," Liu said.

The researchers studied data from 5,916 women in the Missouri Cancer Registry diagnosed with DCIS from 1996 to 2011 and treated with lumpectomy.

Of those women, 1,053 (17.8 percent) received radiation therapy more than eight weeks after surgery, and 1,702 (28.8 percent) did not receive any radiation therapy as part of their initial treatment.

The other 53.4 percent of the patients all received radiation without delay, within the eight-week time frame.

During the average six years of follow-up, 3.1 percent of women developed a recurrence of DCIS or an invasive tumour in the same breast.

For women who received radiation within eight weeks, the rate of recurrence was 2.5 percent.

After adjusting for age, race, pathological factors, surgical margin status and hormone therapy, the risk of breast cancer recurrence was 26 percent higher for women who had delayed radiation therapy and 35 percent higher for women who did not initially receive radiation.

Liu is calling for more extensive research involving a larger group of patients.

"What we've found suggests the need for more studies," she said. "Our hope is to provide clear-cut guidelines that will help more women reduce their risk of recurrence."

The Missouri Department of Health and Senior Services and the University of Missouri oversee the Missouri Cancer Registry.

Source: Washington University School Of Medicine