Treatment outcome of breast-conserving therapy in patients with positive or close resection margins: Japanese multi institute survey for radiation dose effect

BACKGROUND: The relationship between a positive resection margin and the risk of ipsilateral breast tumor recurrence (IBTR) is controversial. To evaluate the radiation dose and other factors influencing the ipsilateral breast tumor control (IBTC) in patients with positive or close resection margins after breast conserving surgery (BCS), the Japanese Radiation Oncology Study Group (JROSG) S-99-3 study group conducted a multi-institute survey of these patients. METHODS: The patients with less than 5 mm tumor-free margins after BCS were eligible for this study. A total of 971 patients from 18 institutes were enrolled in the analysis. The final pathological margin status was classified into 3 groups. Radiation doses to the tumor bed were less than 60 Gy in 252 patients, 60 Gy in 456 patients and more than 60 Gy in 233 patients. RESULTS: IBTR was observed in 55 patients (5.8%). The IBTC rates at 5 and 10 years by the Kaplan Meier method were 95.6% and 87.3%, respectively. There was no significant difference in 10-year IBTC rates according to marginal status; 85.9% in positive margin patients, 91.0% in equal or less than 2 mm margin patients and 87.0% in 2.1-5 mm margin patients. Radiation dose to the tumor bed was a marginally significantly associated with the 10-year IBTC rate (> or = 60 Gy 90.8% vs < 60 Gy 84.2%, p = 0.057). In patients with positive margins, IBTC with radiation dose equal to or more than 60 Gy was significantly better (p = 0.039). The other factors influencing the IBTC were age (> or = 35 years vs < 35 years: p < 0.0001), menopausal status (p < 0.0001) and tumor size (p = 0.023). CONCLUSIONS: In patients with positive margins, IBTC with radiation dose equal to or more than 60 Gy was significantly better than the others. We recommend that the tumor bed be irradiated with at least 60 Gy in the patients with positive margins. Further follow-up is necessary to draw final conclusions.