A new study has found that treating ductal carcinoma in situ (DCIS) with surgery and radiotherapy lowers the risk of developing cancer, although the benefits decline over time.

DCIS is a breast condition that can become invasive cancer as cells lining the milk ducts have begun to turn into cancer cells but have not yet spread into other parts of the breast. The condition is often detected during breast screening. Although only a proportion of DCIS cases will progress into invasive cancer and little is known about which cases will progress, the treatments available for DCIS are similar to treatments for invasive breast cancers.

The new study, presented at the 12th European Breast Cancer Conference, followed patients for up to 27 years. It included 10,045 women diagnosed with DCIS in the Netherlands between 1989 and 2004. Investigators gathered data on whether the women were treated with breast-sparing surgery to remove the DCIS, breast-sparing surgery followed by radiotherapy, or mastectomy. They also collected information on whether the women were subsequently diagnosed with DCIS in the same breast again or with an invasive breast cancer in the same breast.

“Most women who are diagnosed with DCIS are offered surgery to remove the abnormal breast tissue and they are often also offered radiotherapy, even though the majority would not go on to develop invasive breast cancer,” said Maartje van Seijen, PhD, of the Netherlands Cancer Institute, in a press release. “We wanted to look at how this group of women get on in the long term, according to which treatment they received.”

In the first 10 years following diagnosis, women who had breast-sparing surgery but not radiotherapy had a 13% risk of being diagnosed with DCIS again and their risk of invasive breast cancer was 13.9%. Women who received breast-sparing surgery and radiotherapy had a 4.6% risk of DCIS in the first 10 years and 5.2% risk of invasive breast cancer.

Although women who had radiotherapy had lower risks in the first 10 years, the authors found that in the following years, their risks were closer to those for women who had surgery alone. After 10 years post-diagnosis, women who had breast-sparing surgery but not radiotherapy had a risk of 1.2% of being diagnosed with DCIS again and their risk of invasive breast cancer was 11.8%.

In women treated with breast-sparing surgery and radiotherapy, there was a 2.8% risk for DCIS and a 13.2% risk for invasive breast cancer.

“The risk of DCIS or invasive cancer recurring in these women will diminish over time, whether they had just the breast-sparing surgery or breast-sparing surgery with radiotherapy,” van Seijen said in a press release. “This study shows that, overall, the addition of radiotherapy gives women the best chances. However, there remains a chance of a new DCIS or invasive cancer developing that is not related to the initial diagnosis and we would expect this risk to be similar between the 2 types of treatment. In a very small number of women, radiotherapy itself might cause a new breast cancer, often many years after the radiotherapy was given.”

van Seijen added that women who had a mastectomy to treat their DCIS had the lowest risks of invasive cancer, although previous research has shown that overall survival in patients who have a mastectomy is the same as in patients who have less aggressive treatments. Mastectomy would be considered over-treatment in the majority of women with DCIS, whose condition will never become invasive according to van Seijen.

“DCIS is a condition that affects thousands of women and a proportion of them go on to develop invasive breast cancer,” said Emiel Rutgers, MD, PhD, FRCS, president of the European Breast Cancer Council, in a press release. “Most of these women will have decades of life ahead of them so it’s vital that we understand the long-term impact of the treatments we offer.”

REFERENCE
Treating DCIS with surgery and radiotherapy lowers cancer risk but benefits drop over time [news release]. EurekAlert; October 3, 2020. https://www.eurekalert.org/pub_releases/2020-10/eofr-tdw100120.php. Accessed January 11, 2021.