VIENNA, Austria-Clear guidelines for omitting adjuvant radiotherapy (RT) after breast conserving therapy (BCT) for patients with ductal carcinoma in situ (DCIS) were reported at the 2017 St. Gallen International Breast Cancer Conference from a 20-year follow-up of the Randomized SweDCIS trial of 1,046 Swedish women randomly assigned to RT or not after BCT for primary DCIS (Journal of Clinical Oncology 2014;32(32):3613-3618).
"For post-menopausal patients with low- or intermediate-grade DCIS-less than 15 mm and with clear margins-there is an option not to give radiotherapy," said Per Karlsson, MD, PhD, Medical and Radiation Oncologist and Professor of Oncology at Sahlgrenska University Hospital in Gothenburg, Sweden.
Radiotherapy Comparison
The SweDCIS trial found a 12 percent absolute benefit overall between patients having RT compared with those who did not. "After 20 years, 32 percent [had] local failure in comparison to 20 percent [of] those having radiation. So, in absolute terms, this difference was 12 percent," he stated. For in situ events, the benefit from radiation was 10 percent, while for invasive events, it was only 2 percent.
Karlsson noted the SweDCIS study had found no mortality benefit from adding RT to BCT, and the same was true in the other big trials looking at RT in patients with DCIS: the NSABP B-17, EORTC 10853, UK/ANZ DCIS, and the RTOG 9804 studies.
"In all the randomized trials, no breast cancer specific mortality benefit has been seen-just a reduction of local failures and new invasive cancers," he said.
And making the decision of whether or not to add RT to surgical excision required balanced appraisal of the pros and cons to be made jointly by the doctor in close consultation with each patient.
"We discuss other cardiovascular risk factors, other diseases, and also the patient's own thoughts about having a modest increased risk of a recurrence [or even] an invasive breast cancer," Karlsson explained. And he emphasized attitudes differed "a lot" from one patient to another.
If overall survival were the only thing that mattered, he said, RT could be omitted. But for a patient who wanted to do whatever she could to avoid local recurrence of DCIS or invasive breast cancer in the same breast, it was proven that RT halved this risk.
"From the randomized trials, the relative risk reduction is 50 percent," he said. "But in many groups, this comes down to absolute benefits of [only] 3, 4, or 5 percent improvement and a reduction of local failure rate. And that is quite a low value to [justify] the possible risk for radiation."
In some patients, the decision is easier. "Younger patients, and [those with] high-risk DCIS are treated."
Patients who were younger than 50 or had high-grade tumors or necrosis and did not have co-morbidities were more likely to choose RT, Karlsson stated. But those with low or intermediate tumor grade, who were older, had cardiovascular disease or diabetes, were smokers, and were willing to accept a higher rate of local recurrence could consider omitting RT.
Treatment Disadvantages
Although he acknowledged there was a greater risk of invasive breast cancer among patients with DCIS as compared with the general population (1.8 times higher in the SEER database), Karlsson said there was a lack of evidence about how much difference radiation could make to this. "[It] has not been shown that we can impact that."
But there were known disadvantages to using radiation. "There are problems with about 10 percent [of patients] reporting pain from the breast more than 10 years after irradiation," he noted. "And there may be problems with cardiovascular risk factors-but using modern radiotherapy can reduce the dose to the heart in left-sided breast cancers. [When] choosing radiation therapy for these patients, it is very important to have modern radiotherapy techniques and restrict the dose to the heart."
Karlsson's advice to doctors is to engage in "very open-minded communication" with patients about the pros and cons of RT. "All the facts that we know should be considered and all possible side effects. Then make a decision together with the patient [on] how to treat the DCIS."
He also noted that, while some women were guided mostly by the fact that mortality was not being impacted, other women took a different view. "For a lot of patients with relatives having had breast cancer, it's very important not to get invasive breast cancer. But all these aspects must be discussed with patients. And what they think about these aspects is very different between different women," he concluded.
Peter M. Goodwin is a contributing writer.