Abstract: Biomarkers for prognosis of tumours, in hepatocellular carcinoma and other cancers. Measurement of biomarkers for prescription of anticancer immunotherapy targeted against ICOS+ regulatory T cells (TReg), e.g., selecting patients for treatment with an anti-ICOS antibody. Biomarkers comprising: (i) ratio of the number of ICOS FOXP3 double positive cells within a defined radius of influence around ICOS single positive cells to the total number of ICOS single positive cells, (ii) mean distance between each ICOS positive FOXP3 negative cell and its nearest ICOS FOXP3 double positive cell, (iii) proportion of FOXP3 positive cells which are ICOS positive, and (iv) density of ICOS positive cells.