AIMS: Over 30% of patients with non-small cell lung cancer (NSCLC) develop brain metastases. If inoperable, optimal supportive care (OSC), including steroids, and whole brain radiotherapy (WBRT) are generally considered to be standard care, although there is no randomised evidence demonstrating that the addition of WBRT to OSC improves survival or quality of life. MATERIALS AND METHODS: QUARTZ is a randomised, non-inferiority, phase III trial comparing OSC + WBRT versus OSC in patients with inoperable brain metastases from NSCLC. The primary outcome measure is quality-adjusted life years (QALYs). QUARTZ was threatened with both loss of funding and early closure due to poor accrual. A lack of preliminary randomised data supporting the trial's hypotheses was thought to underlie the poor accrual, so, with no knowledge of the data, the independent trial steering committee agreed to the unusual step of releasing interim data. RESULTS: Between March 2007 and April 2010, 151 (of the planned 534) patients were randomised (75 OSC + WBRT, 76 OSC). Participants' baseline demographics included median age 67 years (interquartile range 62-73), 60% male, 50% with a Karnofsky performance status <70; steroid usage was similar in the two groups; 64/75 (85%) received WBRT (20 Gy in five fractions). Median survival was: OSC + WBRT 49 days (95% confidence interval 39-61), OSC 51 days (95% confidence interval 27-57) - hazard ratio 1.11 (95% confidence interval 0.80-1.53) in favour of WBRT. Quality of life assessed using EQ-5D showed no evidence of a difference. The estimated mean QALYs was: OSC + WBRT 31 days and OSC 30 days, difference -1 day (95% confidence interval -12.0 to +13.2 days). CONCLUSION: These interim data indicate no early evidence of detriment to quality of life, overall survival or QALYs for patients allocated to OSC alone. They provide key information for discussing the trial with patients and strengthen the argument for continuing QUARTZ to definitively answer this important clinical question.