Risk factors in breast-conservation therapy.

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To identify clinical and pathologic factors associated with an increased risk of local recurrence following breast-conservation therapy (BCT) to assess the safety of this procedure for all subgroups of patients. The study population consisted of 1,026 patients with clinical stage I and II breast cancer treated between 1979 and 1988 at the Netherlands Cancer Institute. The BCT regimen consisted of local excision and axillary lymph node dissection (ALND) followed by whole-breast irradiation to a total dose of 50 Gy in 2-Gy fractions and boost irradiation (mostly by iridium implant) of 15 to 25 Gy. With a median follow-up duration of 66 months, the actuarial breast recurrence rate was 4% at 5 years, counting all breast recurrences. Univariate analysis showed seven factors to be associated with an increased risk of local recurrence; age, residual tumor at reexcision, histologic tumor type, presence of any carcinoma-in-situ component, vascular invasion, microscopic margin involvement, and whole-breast radiation dose. Three factors remained independently significant after proportional hazard regression analysis: age, margin involvement, and the presence of vascular invasion. When the analysis was repeated, but counting only those breast recurrences that occurred before regional or distant failures, only young age and vascular invasion were independent predictive factors. In the third analysis, factors predicting the necessity of local salvage treatment were analyzed. In this analysis, the possible bias in the former analysis caused by censoring actuarial methods was avoided. The results were the same as in the second analysis, showing young age and vascular invasion as the only independent predictive factors. Breast recurrence rates were 6% for patients less than 40 years of age and 8% for patients with tumors showing vascular invasion. In the absence of risk factors, the breast recurrence rate is only 1% at 5 years. Slightly higher recurrence rates were found in patients less than 40 years of age and in patients with tumors showing vascular invasion. The role of margin involvement is uncertain.