We postulated that locoregional recurrence after limited surgery and radiotherapy for breast cancer might be associated with an additional survival hazard, similar to that of a second primary tumor with the same extent of local and regional disease. Using this hypothesis we examined the likely resultant effect on survival. Our calculations indicated that no statistically significant survival deficit due to such recurrence would be detectable until a randomized controlled trial comparing breast conservation with mastectomy had monitored more than 10,000 patients for more than 10 years. A simple mathematical model predicted 5-year survival rates in a cohort of patients treated with breast conservation of 75%, compared to 83% in those without locoregional recurrence. From the date of locoregional recurrence, a 61% 5-year survival rate was predicted, compared to 83% if no hazard was associated with locoregional recurrence. These predictions were compared with the actuarial survival rates of 499 patients with unilateral breast cancer, 49 of whom had developed locoregional recurrence. From the date of initial treatment, the 5-year survival rate of those whose disease recurred was 79%, compared to 88% for those without locoregional recurrence (p = 0.19). The actuarial 5-year survival rate from the date of locoregional recurrence was 63%. The similarity between the patient data and the predictions of the mathematical model indicates that locoregional failure after breast conservation therapy may result in reduced survival. The lack of a significant survival deficit in our cohort or in controlled trials comparing breast conservation therapy with mastectomy is compatible to th small size of the overall effect.
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