Radiotherapy or tamoxifen after conserving surgery for breast cancers of excellent prognosis: British Association of Surgical Oncology (BASO) II trial

Background. The incidence of local recurrence (LR) after conservative surgery for early breast cancer without adjuvant therapy is unacceptably high even with favourable tumours. The aim of this study was to examine the effect of adjuvant therapies in tumours with excellent prognostic features.

Methods. Patients with primary invasive breast cancer <2cm diameter, grade 1 or good prognosis special type, and node negative, treated by wide local excision (WLE) with clear margins were randomised into a 2X2 clinical trial of factorial design with or without radiotherapy and with or without tamoxifen. Trial entry was allowed to either comparison or both.

Findings. The actuarial breast cancer specific survival in 1135 randomised patients at 10 years was 96%. Randomisation by intention to treat showed that LR after WLE alone was 1.9% per annum vs 0.7% with radiotherapy alone (p<0.001, HR 0.37, CI 0.22-0.61) and 0.8% with tamoxifen alone (p<0.004, HR 0.33, CI 0.15-0.70). No patient randomised to both adjuvant treatments developed LR. Analysis by treatment received showed LR at 2.2% pa. for surgery alone vs 0.8% for either adjuvant radiotherapy or tamoxifen and 0.2% for both treatments.

Conclusions. Even in these patients with tumours of excellent prognosis, LR after conservative surgery without adjuvant therapy was still very high. This was reduced to a similar extent by either radiotherapy or tamoxifen but to a greater extent by the receipt of both treatments.