An epoxytigliane compound or a pharmaceutically acceptable salt thereof and an immune checkpoint inhibitor for use in treating a tumour; wherein the epoxytigliane compound is a compound of formula (I): or a geometric isomer or stereoisomer or a pharmaceutically acceptable salt thereof; wherein R 1 is hydrogen or C 1-6 alkyl; R 2 is -OH or -OR 9 ; R 3 is -OH or -OR 9 ; R 4 and R 5 are independently selected from hydrogen and C 1-6 alkyl; R 6 is hydrogen or -R 10 ; R 7 is hydroxy or OR 10 ; R 8 is hydrogen or C 1-6 alkyl; R 9 is -C 1-20 alkyl, -C 2-20 alkenyl, -C 2-20 alkynyl, -C(O)C 1-20 alkyl, -C(O)C 2-20 alkenyl, -C(O)C 2-20 alkynyl, -C(O)cycloalkyl, -C(O)C 1-10 alkylcycloalkyl; -C(O)C 2-10 alkenylcycloalkyl, -C(O)C 2-10 alkynylcycloalkyl, -C(O)aryl, -C(O)C 1-10 alkylaryl, -C(O)C 2-10 alkenylaryl, -C(O)C 2-10 alkynylaryl, -C(O)C 1-10 alkylC(O)R 11 , -C(O)C 2-10 alkenylC(O)R 11 , -C(O)C 2-10 alkynylC(O)R 11 , -C(O)C 1-10 alkylCH(OR 11 )(OR 11 ), -C(O)C 2-10 alkenylCH(OR 11 )(OR 11 ), -C(O)C 2-10 alkynylCH(OR 11 )(OR 11 ), -C(O)C 1-10 alkylSR 11 , -C(O)C 2-10 alkenylSR 11 , -C(O)C 2-10 alkynylSR 11 , -C(O)C 1-10 alkylC(O)OR 11 , -C(O)C 2-10 alkenylC(O)OR 11 , -C(O)C 2-10 alkynylC(O)OR 11 , -C(O)C 1-10 alkylC(O)SR 11 , -C(O)C 2-10 alkenylC(O)SR 11 , -C(O)C 2-10 alkynylC(O)SR 11 , or R 10 is -C 1-6 alkyl, -C 2-6 alkenyl, -C 2-6 alkynyl, -C(O)C 1-6 alkyl, -C(O)C 2-6 alkenyl, -C(O)C 2-6 alkynyl, -C(O)aryl, -C(O)C 1-6 alkylaryl, -C(O)C 2-6 alkenylaryl, or -C(O)C 2-6 alkynylaryl; and R 11 is hydrogen, -C 1-10 alkyl, -C 2-10 alkenyl, -C 2-10 alkynyl, cycloalkyl or aryl; wherein each alkyl, alkenyl, alkynyl, cycloalkyl or aryl group is optionally substituted; and wherein the immune checkpoint inhibitor is an antagonist of one of the following Programmed Death 1 (PD-1) receptor, its ligand PD-L1 and Cytotoxic T-Lymphocyte-Associated protein 4 (CTLA-4). R 1 is hydrogen or C 1-6 alkyl; R 2 is -OH or -OR 9 ; R 3 is -OH or -OR 9 ; R 4 and R 5 are independently selected from hydrogen and C 1-6 alkyl; R 6 is hydrogen or -R 10 ; R 7 is hydroxy or OR 10 ; R 8 is hydrogen or C 1-6 alkyl; R 9 is -C 1-20 alkyl, -C 2-20 alkenyl, -C 2-20 alkynyl, -C(O)C 1-20 alkyl, -C(O)C 2-20 alkenyl, -C(O)C 2-20 alkynyl, -C(O)cycloalkyl, -C(O)C 1-10 alkylcycloalkyl; -C(O)C 2-10 alkenylcycloalkyl, -C(O)C 2-10 alkynylcycloalkyl, -C(O)aryl, -C(O)C 1-10 alkylaryl, -C(O)C 2-10 alkenylaryl, -C(O)C 2-10 alkynylaryl, -C(O)C 1-10 alkylC(O)R 11 , -C(O)C 2-10 alkenylC(O)R 11 , -C(O)C 2-10 alkynylC(O)R 11 , -C(O)C 1-10 alkylCH(OR 11 )(OR 11 ), -C(O)C 2-10 alkenylCH(OR 11 )(OR 11 ), -C(O)C 2-10 alkynylCH(OR 11 )(OR 11 ), -C(O)C 1-10 alkylSR 11 , -C(O)C 2-10 alkenylSR 11 , -C(O)C 2-10 alkynylSR 11 , -C(O)C 1-10 alkylC(O)OR 11 , -C(O)C 2-10 alkenylC(O)OR 11 , -C(O)C 2-10 alkynylC(O)OR 11 , -C(O)C 1-10 alkylC(O)SR 11 , -C(O)C 2-10 alkenylC(O)SR 11 , -C(O)C 2-10 alkynylC(O)SR 11 , or R 10 is -C 1-6 alkyl, -C 2-6 alkenyl, -C 2-6 alkynyl, -C(O)C 1-6 alkyl, -C(O)C 2-6 alkenyl, -C(O)C 2-6 alkynyl, -C(O)aryl, -C(O)C 1-6 alkylaryl, -C(O)C 2-6 alkenylaryl, or -C(O)C 2-6 alkynylaryl; and R 11 is hydrogen, -C 1-10 alkyl, -C 2-10 alkenyl, -C 2-10 alkynyl, cycloalkyl or aryl; wherein each alkyl, alkenyl, alkynyl, cycloalkyl or aryl group is optionally substituted; and wherein the immune checkpoint inhibitor is an antagonist of one of the following Programmed Death 1 (PD-1) receptor, its ligand PD-L1 and Cytotoxic T-Lymphocyte-Associated protein 4 (CTLA-4). <EOS>