Purpose: To determine if more patients (pts) with painful liver cancer have improved pain 1 month following radiation therapy (RT), compared to best supportive care (BSC). Methods: This multi-centre, phase III trial randomized pts with painful hepatocellular carcinoma (HCC) or liver metastases (LM) 1:1 to BSC alone or with single fraction RT (8 Gy). Eligible pts had end-stage disease unsuitable for local, regional or systemic therapies, > 4 weeks since chemotherapy or TACE, > 2 weeks since targeted therapy or immunotherapy, and no planned systemic therapy. The primary objective was to determine if the proportion of pts with improved liver cancer pain "intensity at worst" on Brief Pain Inventory (BPI) by ≥2 points from baseline to 1 month was higher following RT vs. BSC alone. Secondary endpoints included proportion of pts 1) alive at 3 months, 2) with improvement ≥2 points in BPI at 1 and 3 months, 3) with a 25% reduction in opioids at 1 month and 4) with improved quality of life (QOL): Functional Assessment of Cancer Therapy-Hepatobiliary (FACT-Hep) hepatobiliary subscale (HBS) change score ≥5 and Trial Outcome Index ≥7 at 1 month. Results: Sixty-six pts were randomized, 43 with LM (12 colorectal, 5 breast, 4 pancreas, 3 lung, 19 other), 23 with HCC. 59% had ECOG performance status 2 or 3, 64% Child Pugh (CP) score A vs. 36% CP B or C. The clinical target volume irradiated was the whole liver or near whole liver (median 2013 cc). Forty-two pts (24 on RT and 18 on BSC) completed baseline and 1-month assessments. The average baseline pain at worst score was 7/10. A significant improvement in the primary endpoint, ‘worst’ pain score on BPI, from baseline to 1 month was seen in 67% of pts on RT and 22% on BSC (p = 0.004). The proportion of pts with improved ‘worst’ pain at 1 month, with no increase in opioid use was 21% on RT vs 0% with BSC (p = 0.07). From baseline to 1 month, the proportion of pts with a significant improvement in BPI “pain at its least” was higher for pts on RT vs. BSC (63% vs. 28%, p = 0.03), as was BPI “percentage relief in pain by treatment” (59% vs. 25%, p = 0.04). A sensitivity analysis of all pts, treating those with no 1 month assessment as having ‘no improvement’, found improvements in BPI ‘worst’ pain in 49% of pts on RT and 12% for BSC alone (p = 0.002). Eleven patients on the BSC arm crossed over to receive RT at 1 month. A trend to improvement in FACT HBS post RT vs BSC was seen at 1 month (p = 0.07), with no statistically significant difference in other FACT-Hep subscales. The proportion of pts with grade ≥2 AE (CTCAEv4.0) at day 30 was 58% on RT vs 33% on BSC (p = 0.05). Grade ≥3 AE were uncommon. There was a trend for improved 3 month survival with RT (51% vs. 33% for BSC alone, p = 0.07). Conclusions: Single fraction RT (8 Gy) improves hepatic pain in the majority of patients with end-stage HCC or liver metastases, with a trend to improved survival. This research is funded by the Canadian Cancer Society (Grant #703547). Clinical trial information: NCT02511522.