A booster dose of radiotherapy added to regular treatment may help stop young women with very early breast cancer from progressing to a more serious form of the disease, researchers said on Thursday.

Ductal carcinoma in situ (DCIS) is contained within the cells lining the milk ducts of the breast that has not yet spread to the surrounding breast tissue. Surgery is usually performed to remove the cells and prevent recurrence. If the DCIS is extensive, a mastectomy may be necessary. Radiotherapy can also be used to kill any remaining cancer cells.

Scientists who compared different treatments for DCIS said their findings show radiotherapy plus a boost dose improves the patients’ chances.

“First, not using radiotherapy in young patients with DCIS resulted in an unacceptable number of women having their cancer return and second, these patients benefit from an additional boost dose,” said Guenther Gruber of the Kantonsspital in Aarau, Switzerland.

He and a team of researchers analyzed the outcomes of 373 women 45 years old or younger who had been treated at 18 different institutions throughout the world for DCIS.

One sixth had surgery to remove the DCIS. Nearly half had surgery plus radiotherapy, and the remainder had surgery, radiotherapy and a boost dose.

The risk of a recurrence of DCIS or invasive breast cancer decreased with each additional treatment.

“Our findings clearly suggest that the radiation dose is very important for local tumor control for patients with DCIS aged 45 years or younger,” Gruber said in a report in The Lancet Oncology journal.

Advances in breast screening have led to an increase in the number of women diagnosed with DCIS. If it is not treated, DCIS can develop into invasive cancer.

Although more research is needed, the scientists said radiotherapy of the whole breast followed by a boost dose should be considered for breast-conserving treatment in young patients with DCIS.