It will examine how clonal dominance and intratumour heterogeneity influence outcomes after treatment, offering a unique opportunity to decipher mechanisms of resistance to immunotherapy with anti-PDL1. These data will help improve future study design by developing greater understanding of patient selection for immunotherapies in patients with NSCLC. The relationship between intratumour heterogeneity and cfDNA/CTCs will also be explored in DARWIN II, which may develop tools for patient selection and monitoring to be examined further in future studies. Results from DARWIN II will help to identify a biomarker for anti-PD-L1 therapy which could be used for patient stratification in future phase III trials of molecules targeting this T-cell inhibitory checkpoint. DARWIN II will also provide preliminary data on efficacy of MPDL3280A, which could be used to design randomised studies.