Postoperative radiotherapy after DCIS: Useful for whom?

The number of patients with ductal carcinoma in situ (DCIS) increases with more widely used screening mammography programs. DCIS accounts for approximately 20% of all new breast cancer diagnoses in these programs and the natural course of this heterogeneous group of pre-invasive lesions is not fully known. Better definition of subgroups benefitting from radiotherapy and knowledge on the natural course of DCIS are important issues for the future management of DCIS. Four large randomized trials have studied the effects of postoperative radiotherapy after breast conserving surgery in patients with wider spectrum of DCIS and all of them have shown radiotherapy to halve the risk of ipsilateral events, however, without any significant effect on breast cancer mortality. SweDCIS is one of these four randomized trials (n = 1046) and with 20 years follow-up the relative risk reduction for an ipsilateral event was 37.5% and the absolute reduction was 12%. For an in-situ ipsilateral event the absolute reduction was 10% and for an invasive ipsilateral event the reduction was 2%. The reduction of new events in the SweDCIS was most evident during the first decade after treatment. In RTOG 9804 patients in a good-risk subset of DCIS were randomized to radiotherapy or not and with seven years of follow-up the ipsilateral local failure rate was 0.9% and 6.7% in the two arms, respectively. Radiotherapy to the conserved breast may also give long-term side effects in a small proportion of the patients, in which experience of breast pain is the most common, reported in about 10% of the patients. With modern radiotherapy techniques the dose to the heart can be restricted to low levels and meta-analyses from the randomized DCIS trials showed no difference in non-breast cancer mortality. Several factors in different trials have shown to influence the risk for an ipsilateral event: age, size, grade, necrosis, clear margin, and detected on mammography or not. But identification of subgroups without relative efficacy of radiotherapy has been challenging to find. The Van Nuys prognostic index and the nomogram from the Memorial Sloan-Kettering take several of these factors into account. These and genomic assays may help to optimize the treatments of patients with DCIS. Still, radiotherapy after breast conserving surgery is the standard of care for a majority of DCIS patients. For some low risk DCIS patients accepting a slight increased risk of an ipsilateral event it is reasonable to omit radiotherapy after close communication with the patient about pros and cons of radiotherapy.