P4-18-04: Hypofractionated Radiotherapy for Breast Ductal Carcinoma In Situ.

Background Conventional radiotherapy at a dose of 50 Gy in 25 fractions after breast conservative surgery is the standard treatment for ductal carcinoma in situ of the breast (DCIS). Hypofractionation is an interesting alternative for the treatment of breast cancer, providing a less intense treatment scheme for the patient. While the hypofractionated regimen of 42.5 Gy in 16 fractions has been shown to be equivalent to 50 Gy in 25 in infiltrating ductal carcinoma, few studies and no prospective study have reported results using hypofractionation in DCIS. Materials and Methods : In this multicenter collaborative effort, we retrospectively reviewed the records of women with a diagnosis of DCIS at two Canadian institutions, treated with conservative surgery followed by hypofractionated radiotherapy (42.5 Gy in 16 fractions) to the whole breast. Tumor, patient and treatment factors were collected. Local control was evaluated using the Kaplan Meier method. Curves were compared using log rank. Results : Between 2003 to 2008, 292 patients with DCIS underwent conservative surgery followed by hypofractionated radiation in 16 fractions for a total dose of 42.5 Gy. Treatment delivery was similar at both institutions. Mean age at diagnosis was 59 years, with 70 % of women being postmenopausal. Nuclear grade was 1–2 in 65 % of patients while 28 % had grade 3 tumors. Complete surgical excision with negative margins was achieved in 92 % of patients. Radiotherapy boost was given to 92 patients (31.5 %) at the discretion of the radiation oncologist. After a mean follow up of 3.35 years (range 1–8 years), 10 patients (3.4 %) had ipsilateral local relapse resulting in a disease-free survival (DFS) of 96 % at 4 years. The histology at recurrence was DCIS for 8 patients; infiltrative disease for one patient and one patient had an unknown histology at recurrence. Age was statistically associated with local relapse (DFS 89 % for patients under 50 years old vs 97 % for those older than 50, p=0.027). Grade was also a significant prognostic factor (DFS 98% for grade 1–2 vs 91 % for grade 3, p = 0.015). Finally, administration of boost did not have an impact on local control (DFS boost 98 % vs 95 % for no boost, p=0.44). Discussion : Hypofractionated radiotherapy (42.5 Gy in 16 fractions) provides excellent local control for patients with DCIS undergoing breast conservative surgery. This regimen is more convenient to both patient and physician since it is less time consuming. Further work needs to be done to determine if this regimen is as effective as conventional radiotherapy in younger women (age less than 50) and those with grade 3 tumors. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-18-04.