Partial breast radiotherapy after breast conservation: 5 year outcomes from the IMPORT LOW (CRUK/06/003) phase III trial (2017)

Type of publication:
Conference abstract

Coles C.; Griffin C.; Bhattacharya I.; Emson M.; Haviland J.; Hopwood P.; Kaggwa R.; Bliss J.; Kirby A.; Donovan E.; *Agrawal R.; Alhasso A.; Brunt A.M.; Ciurlionis L.; Chan H.; Harnett A.; Sawyer E.; Sybdikus I.; Tsang Y.; Wheatley D.; Wilcox M.; Yarnold J.; Jefford M.

Radiotherapy and Oncology; May 2017; vol. 123

Background: Local cancer relapse rates after breast conservation surgery followed by radiotherapy have fallen sharply in many countries with risk influenced by patient age and clinico-pathological factors. In women at lower than average risk of local relapse, partial breast radiotherapy restricted to the vicinity of the original tumour is hypothesised to improve the balance of beneficial versus adverse effects compared with whole breast radiotherapy. Methods: The IMPORT LOW trial (ISRCTN12852634) recruited women aged >=50 years after breast conserving surgery for invasive ductal adenocarcinoma pT<=3cm, pN0- 3, G1-3 and >=2mm resection margins. Using 15 daily treatments, patients were randomly allocated (1:1:1) to 40 Gy whole breast radiotherapy (control), 36 Gy whole breast plus 40 Gy to partial breast (reduced dose) or 40 Gy partial breast only (partial breast). Primary endpoint was ipsilateral local relapse rate (80% power to exclude a +2.5% noninferiority margin at 5 years for each test group). Findings: Between May 2007 and October 2010, 2018 women were recruited (control n=675, reduced dose: n=674, partial breast: n=669). With a 72.2 month median followup (IQR 61.7-83.2), 5-year local relapse rates were 1.1% (95%CI 0.5-2.3), 0.2% (0.02-1.2) and 0.5% (0.2-1.4) in control, reduced dose and partial breast groups. Absolute differences in local relapse rate compared with the control group were -0.73% (-0.99, 0.22) for the reduced dose and -0.38% (-0.84, 0.90) for the partial breast groups, demonstrating non-inferiority for both test groups. Photographs, patients and clinicians reported similar or lower levels of adverse effects after reduced dose or partial breast radiotherapy compared with whole breast radiotherapy (see Table 1). (Table presented) Interpretation: At 5 years, partial breast and reduced
dose radiotherapy showed local relapse rates non-inferior to that observed following whole breast radiotherapy and produced equivalent or milder late normal tissue side effects. This simple radiotherapy technique is implementable in radiotherapy centres worldwide.