The Impact of Boost Dose and Margins on the Local Recurrence Rate in Breast Conserving Therapy: Results From the EORTC Boost-No Boost Trial

Article Outline

• Purpose/Objective(s)
• Materials/Methods
• Results
• Conclusions
• Copyright

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Purpose/Objective(s) 

To investigate the long term impact of a boost dose and margins of tumorectomy on local control, who underwent lumpectomy and whole breast irradiation as part of their breast conserving therapy (BCT) for stage I and II breast cancer.

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Materials/Methods 

All patients underwent tumorectomy followed by whole breast irradiation of 50 Gy. Patients having a microscopically complete excision (N = 5318) received no boost or a 16-Gy boost, while patients with a microscopically incomplete excision received a boost dose of 10 or 26 Gy (N = 251).In a subgroup of 1725 patients with central pathology review clinical and pathologic characteristics were evaluated in relation to final margin status (FMS) including age, tumor size, volume of excision, receptor status, histology, and use of adjuvant systemic therapy. In the study population, the FMS was negative in 73% (n = 1162), positive in 6% (n = 102), and close (<2 mm) in 21% (N = 332) of the patients respectively.

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Results 

Local recurrence was reported as the first failure in 278 patients with no boost vs. 165 patients with boost; at 10 years, the cumulative incidence of local recurrence was 10.2% vs. 6.2% for the no boost and the boost group, respectively (p < 0.0001). The hazard ratio of local recurrence was 0.59 (0.46–0.76) in favour of the boost, with no statistically significant interaction per age group. The absolute risk reduction at 10 year per age group was the largest in patients 40 years or less: 23.9% to 13.5% (p = 0.0014). At 10 years, the cumulative incidence of local recurrence in the incomplete resected patients was 17.5% vs. 10.8% for the 10 Gy boost and for the 26 Gy boost respectively (p > 0.1).

In the subgroup with margin evaluation by the central pathologist the local failure rate for patients with negative margins at 10-years was 9.4% compared with 11.1% for patients with positive margins. Age, receptor status, systemic treatment, boost, grade of the invasive tumor, EIC and DCIS were involved as confounding factors. In the multivariable analysis of local control, the boost (p = 0.001), higher age (p < 0.0001) were associated with a lower local recurrence rate. In the multivariable analysis of local failure, the margin of the invasive tumor was not statistically significant (p = 0.39, HR 0.98 (0.94; 1.03)). In addition, the effect of the margin status on local control was not found to be dependent on age, systemic or boost treatment.

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Conclusions 

A boost dose of 16 Gy significantly improved local control in patients with complete excision; the largest absolute benefit was seen in young patients. In the subgroup of patients with central pathology review margin status was not associated with increased risk of local recurrence, while age and boost were independent factors associated with local control.