Effect of time interval between breast-conserving surgery and radiation therapy on ipsilateral breast recurrence

Purpose: To examine the effect of the time interval (interval) between brea st-conserving surgery (BCS) and the start of radiation therapy (RT) on the subsequent risk of ipsilateral breast cancer recurrence (IBR), Methods and Materials: We reviewed interval and a number of prognostic and treatment factors among 1,962 women treated with BCS and RT for invasive br east cancer diagnosed between January 1, 1989 and December 31, 1993 in Brit ish Columbia, Canada. Subjects were female, less than 90 years old at diagn osis, not treated with chemotherapy, not stage T4 or M1, and had survived m ore than 30 days from diagnosis. The cumulative incidence of IBR was estima ted in four interval groups: 0-5, 6-8, 9-12, and 13+ weeks. Only 23 women h ad an interval of greater than 20 weeks between BCS and start of RT, To ass ess whether an imbalance of prognostic and treatment factors could be obscu ring real differences between the interval groups, Cox proportional hazards regression analyses were conducted, Results: Median follow-up was 71 months. The crude incidence of IBR for the entire sample was 3.9%. The cumulative incidence of IBR in the 6-8, 9-12, and 13+ week groups was not statistically significantly different from the cumulative incidence of IBR in the 0-5 week group. Multivariate analyses de monstrated that patients not using tamoxifen (p = 0.027) and those with gra de 3 histology (p = 0.003) were more likely to recur in the breast. Interva l between BCS and RT was not a statistically significant predictor of breas t recurrence when entered into a model incorporating tamoxifen use and tumo r grade (0-5 vs, 6-8 weeks, p = 0.872; 0-5 vs. 9-12 weeks, p = 0.665; 0-5 v s. 13+ weeks, p = 0.573). Conclusions: We found no univariate or multivariate difference in ipsilater al breast cancer recurrence between intervals of 0 to 20 weeks from breast conserving surgery to start of radiation therapy, in a population-based, lo w risk group of women not receiving adjuvant chemotherapy, after controllin g for other factors important in predicting ipsilateral breast cancer recur rence. (C) 2000 Elsevier Science Inc.