Radiotherapy after mastectomy for screen-detected ductal carcinoma in situ

Background A role for radiotherapy after mastectomy for ductal carcinoma in situ (DCIS) is unclear. Using a prospective audit of DCIS detected through the NHS Breast Screening Programme we sought to determine a rationale for the use of post mastectomy radiotherapy for DCIS. Methods Over a nine year period, from 9972 patients with screen-detected DCIS and complete surgical, pathology, radiotherapy and follow up data, 2944 women underwent mastectomy for DCIS of whom 33 (1.1%) received radiotherapy. Results Use of post mastectomy radiotherapy was significantly associated with a close (<1 mm) pathology margin (χ²(1) 95.81; p < 0.00001), DCIS size (χ² (3) 16.96; p < 0.001) and the presence of microinvasion (χ²(1) 3.92; p < 0.05). At a median follow up 61 months, no woman who received radiotherapy had an ipsilateral further event, and only 1/33 women (3.0%) had a contralateral event. Of the women known not to have had radiotherapy post mastectomy, 45/2894 (1.6%) had an ipsilateral further event and 83 (2.9%) had a contralateral event. Conclusion Recurrence following mastectomy for DCIS is rare. A close (<1 mm) margin, large tumour size and microinvasion, may merit radiotherapy to reduce ipsilateral recurrence.