Background: TAS-102 is an orally administered combination of the thymidine-based nucleic acid analogue, trifluridine and the thymidine phosphorylase inhibitor, tipiracil hydrochloride. Following the phase III RECOURSE study, it received approval as third line treatment for metastatic colorectal cancer showing significant improvement in overall and progression free survival and an acceptable toxicity profile. Methods: We performed a multicenter retrospective observational study of patients with metastatic colorectal cancer receiving TAS-102 as third line treatment between 2016 and 2018 in Cancer centers across the UK. Results: A total of 143 patients were included (94 men, 49 women). Median age was 68 years (35-82). All patients had received at least 2 lines of fluoropyrimidine-based chemotherapy doublet with oxaliplatin or irinotecan. About 90% of patients had ECOG ≥ 1. Median duration of treatment was 2.9 months (0.5-22.9), with a response rate of 1.6% and stable disease achieved in 24%. Median OS was 7 months (95% CI 5.84-8.15) and median PFS 2.6 months (95% CI 2.2-3.36). A dose reduction was required in 28% of patients, while 8% discontinued treatment due to toxicity. AEs reported included fatigue 81.3% (G3 16.8%), nausea 34.5% (G3 4.5%) and diarrhoea 25.5% (G3 1.8%). Neutropenia was common 50.4%, (≥ G3: 25.4%) with 4.2% cases of neutropenic fever while thrombocytopenia was less frequent 8.7% (≥ G3 1.8%). Conclusions: The OS, PFS and ORR observed in our real-world experience were consistent with the RECOURSE trial, though we noted a lower disease control rate. Overall, TAS-102 was well tolerated and the most prevalent adverse events seen in our patients were in keeping with those reported in the trial. Although severe toxicities were less frequent than the trial, we experienced higher rates of toxicity induced dose reductions and treatment cessations, which could reflect the differences between trial and real world populations. Further validation is warranted.