An antitumor formulation comprising a biphenyl compound represented by Formula or a salt thereof and one or more other antitumor agents for use in combination in a method of treating and/or preventing a tumor: wherein ring A represents a monocyclic, bridged cyclic, or spirocyclic 4- to 14-membered nitrogen-containing saturated heterocyclic group having 1 to 3 nitrogen atoms, 0 to 1 sulfur atoms, and 0 to 2 oxygen atoms as heteroatoms; ring B represents monocyclic or bicyclic 5- to 14-membered unsaturated hydrocarbon or a monocyclic or bicyclic 5- to 14-membered unsaturated heterocyclic group that may be substituted with oxo, that has 0 to 4 nitrogen atoms, 0 to 2 sulfur atoms, and 0 to 3 oxygen atoms as heteroatoms, and that has at least one of nitrogen, sulfur, and oxygen; R1 represents nitro or cyano; R2 represents halogen; R3 represents amino, mono- or di(C1-C6 alkyl)amino, (C3-C7 cycloalkyl)amino, or C1-C6 alkyl; R4 represents halogen, nitro, cyano, carboxy, substituted or unsubstituted C1-C8 alkyl, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C3-C7 cycloalkyl, mono- or di(C1-C6 alkyl)amino, or substituted or unsubstituted carbamoyl; when at least one R4 represents substituted C1-C8 alkyl, substituted C2-C6 alkenyl, substituted C1-C6 alkoxy, substituted C3-C7 cycloalkyl, or substituted carbamoyl, the substituent is halogen, carboxy, C1-C6 alkoxy, hydroxy, C1-C6 alkyl that may be substituted with hydroxy, monocyclic 5- to 10-membered unsaturated hydrocarbon, carbamoyl that may be substituted with C1-C6 alkyl or monocyclic 5- to 10-membered unsaturated hydrocarbon, (C2-C7 acyl)oxy, amino that may be substituted with C1-C6 alkyl or C2-C7 acyl, C3-C7 cycloalkyl that may be substituted with hydroxy, or (C1-C6 alkoxy)(C1-C6 alkyl); when two or more of the substituents are present, the substituents may be identical or different; R5 and R6 may be identical or different, and each represent hydrogen or C1-C6 alkyl; R5 and R6 may otherwise form oxo or thioxo together; when R5 and R6 are identical or different, and each represent hydrogen or C1-C6 alkyl, at least one of R5 and R6 is hydrogen; l represents an integer of 0 to 2; m represents an integer of 0 to 2; n represents an integer of 0 to 5; when l is 2, two R2s may be identical or different; when m is 2, two R3s may be identical or different; when n is 2 to 5, two to five R4s may be identical or different. ring A represents a monocyclic, bridged cyclic, or spirocyclic 4- to 14-membered nitrogen-containing saturated heterocyclic group having 1 to 3 nitrogen atoms, 0 to 1 sulfur atoms, and 0 to 2 oxygen atoms as heteroatoms; ring B represents monocyclic or bicyclic 5- to 14-membered unsaturated hydrocarbon or a monocyclic or bicyclic 5- to 14-membered unsaturated heterocyclic group that may be substituted with oxo, that has 0 to 4 nitrogen atoms, 0 to 2 sulfur atoms, and 0 to 3 oxygen atoms as heteroatoms, and that has at least one of nitrogen, sulfur, and oxygen; R1 represents nitro or cyano; R2 represents halogen; R3 represents amino, mono- or di(C1-C6 alkyl)amino, (C3-C7 cycloalkyl)amino, or C1-C6 alkyl; R4 represents halogen, nitro, cyano, carboxy, substituted or unsubstituted C1-C8 alkyl, substituted or unsubstituted C2-C6 alkenyl, substituted or unsubstituted C1-C6 alkoxy, substituted or unsubstituted C3-C7 cycloalkyl, mono- or di(C1-C6 alkyl)amino, or substituted or unsubstituted carbamoyl; when at least one R4 represents substituted C1-C8 alkyl, substituted C2-C6 alkenyl, substituted C1-C6 alkoxy, substituted C3-C7 cycloalkyl, or substituted carbamoyl, the substituent is halogen, carboxy, C1-C6 alkoxy, hydroxy, C1-C6 alkyl that may be substituted with hydroxy, monocyclic 5- to 10-membered unsaturated hydrocarbon, carbamoyl that may be substituted with C1-C6 alkyl or monocyclic 5- to 10-membered unsaturated hydrocarbon, (C2-C7 acyl)oxy, amino that may be substituted with C1-C6 alkyl or C2-C7 acyl, C3-C7 cycloalkyl that may be substituted with hydroxy, or (C1-C6 alkoxy)(C1-C6 alkyl); when two or more of the substituents are present, the substituents may be identical or different; R5 and R6 may be identical or different, and each represent hydrogen or C1-C6 alkyl; R5 and R6 may otherwise form oxo or thioxo together; when R5 and R6 are identical or different, and each represent hydrogen or C1-C6 alkyl, at least one of R5 and R6 is hydrogen; l represents an integer of 0 to 2; m represents an integer of 0 to 2; n represents an integer of 0 to 5; when l is 2, two R2s may be identical or different; when m is 2, two R3s may be identical or different; when n is 2 to 5, two to five R4s may be identical or different.