CLINICAL SYMPOSIUM 18 November 2022 10.30–12.00: Questions for Innovations in Radiotherapy| Volume 175, SUPPLEMENT 1, S1-S2, November 2022

Randomised controlled trial of breast conserving therapy: 30 year analysis of the Scottish breast conservation trial

      Background: The standard of care for most early breast cancer patients is breast conserving surgery (BCS), adjuvant radiotherapy (RT) and systemic therapy. Several trials have confirmed that RT reduces local recurrence, but there are few reports of trials with longterm follow up assessing the impact of omission of RT on overall survival. The Scottish Conservation trial of BCS & systemic therapy appropriate to ER status ± postoperative whole breast RT (Forrest et al. Lancet 1996;348:708–13) showed ipsilateral breast tumour recurrence (IBTR) of 24.5% in the no RT arm and 5.8% in the RT arm but no difference in overall survival at 6 years after randomisation. We report the long-term impact within this study of postoperative loco-regional RT or its omission on IBTR, overall survival, regional recurrence, metastases and breast cancer deaths.
      Methods: 585 patients aged ≤70 years with early breast cancer ≤4cm (T0, T1a, T2a, N0, N1a, N1b, M0) underwent local excision with a 1 cm margin, axillary node sampling or axillary node clearance. Adjuvant systemic therapy of tamoxifen or CMF was given dependent on ER status. Patients were stratified by menopausal and ER status (≥20,<20, unknown) then randomised to RT (291) versus noRT (294). Clinical outcomes were compared by Log-Rank test. Point estimates for actuarial rates at 10, 20 and 30 years are given in the table. Hazard ratios (HR) are reported with no RT as the reference. Failures of the proportional hazards (PH) assumption are reported if significant.
      Results: The two arms were well balanced for age, menopausal status, adjuvant systemic therapy, type of axillary surgery, laterality, tumour size, grade, histological type, nodal status and ER status. IBTR was significantly lower in the RT arm: HR = 0.39 (95%CI 0.27–0.55), although there was evidence of a failure of the PH assumption (p < 0.0001). The Log Rank test was similarly statistically significant (p < 0.0001). Exploration of the hazard rate suggests that there are differences in the first 10 years after treatment, but beyond that the risk is similar in both arms. There was no difference in overall survival, HR = 1.08 (95% CI 0.89, 1.30), p = 0.43, with survival rates similar to 30 years (table 1).
      Tabled 1
      Rate (95% CI)10 years20 years30 years
      LR8.8% (5.3, 12.2%)31% (25.5, 36.5%)15.2% (10.2, 20.2%)37.6% (31.6, 43.7%)27.8% (19.0, 36.5%)42.7% (35.8, 49.6%)
      OS72.5% (67.3, 77.6%)70.8% (65.5, 76.0%)48.6% (42.7, 54.4%)48.4% (42.5, 54.2%)23.7% (18.3, 29.0%)27.5% (22.0, 32.9%)
      Conclusions: Adjuvant loco-regional RT with systemic therapy appropriate to ER status reduces the risk of IBTR in the first 10 years of follow up but has no impact thereafter on IBTR nor on overall survival up to 30 years.
      No conflict of interest.