Does delay in breast irradiation following conservative breast surgery in node-negative breast cancer patients have an impact on risk of recurrence?

PURPOSE: This retrospective review was conducted to determine if delay in the start of radiotherapy after definitive breast surgery had any detrimental effect on local recurrence or disease-free survival in node-negative breast cancer patients. METHODS AND MATERIALS: A total of 568 patients with T1-T2, N0 breast cancer were treated with breast-conserving surgery and breast irradiation, without adjuvant systemic therapy between January 1, 1985 and December 31, 1992, at the London Regional Cancer Centre. Adjuvant breast irradiation consisted either of 50 Gy in 25 fractions or 40 Gy in 15 or 16 fractions, followed by a boost of 10 Gy or 12.5 Gy to the lumpectomy site. The time intervals from definitive breast surgery to breast irradiation used for analysis were 0-8 weeks (201 patients), > 8-12 weeks (235 patients), > 1216 weeks (91 patients), and > 16 weeks (41 patients). The time intervals of 0-12 weeks (436 patients) and > 12 weeks (132 patients) were also analyzed. Kaplan-Meier estimates of time to local recurrence and disease-free survival rates were calculated. The association between surgery-radiotherapy interval, age (< or = 40, > 40 years), tumor size (< or = 2, > 2cm), Scharf-Bloom-Richardson (SBR) grade, resection margins, lymphatic vessel invasion, extensive intraductal component, and local recurrence and disease-free survival were investigated using Cox regression techniques.
RESULTS: Median follow-up was 63.5 months. Patients in all 4 time intervals were similar in terms of age and pathologic features. There was no statistically significant difference between the 4 groups in local recurrence or disease-free survival with surgery-radiotherapy interval (p = 0.189 and p = 0.413, respectively). The 5-year freedom from local relapse was 95.4%. The crude local recurrence rate was 6.9% (7.8% for 436 patients treated within 12 weeks (median follow-up 67 months) and 3.8% for 132 patients treated > 12 weeks from surgery (median follow-up 52 months). In a stepwise multivariable Cox regression model for disease-free survival, allowing for entry of known risk factors, tumour size (p < 0.001), grade (p < 0.001), and age (p = 0.048) entered the model, but the surgery-radiotherapy interval did not enter the model.
CONCLUSION: This retrospective study suggests that delay in start of breast irradiation beyond 12 and up to 16 weeks does not increase the risk of recurrence in node-negative breast cancer patients. The certainty of these results are limited by the retrospective nature of this analysis and the lack of information concerning the late local failure rate.