A pharmaceutical composition for use in a method for treating thyroid cancer, comprising: the arylethene derivative represented by the following Chemical Formula 1: wherein L is (C6-C20)arylene, (C3-C20)heteroarylene, or (C3-C20)fused heterocycle; R 1 is (C3-C20)heterocycloalkyl, (C3-C20)heteroaryl, - O-(CH 2) m -R 11, -(CH 2) m -R 12, -NH-(CH 2) m -R 13, -NHCO-(CH 2) n -R 14, or -SiR 16 R 17 -(CH 2) m -R 15; R 11 to R 15 are independently of one another (C3-C20)heterocycloalkyl; R 16 and R 17 are independently of each other (C1-C20)alkyl; m is an integer of 1 to 3; and n is an integer of 0 or 1; Ar is (C6-C20)aryl or (C3-C20)heteroaryl, in which the aryl or heteroaryl of Ar may be further substituted by one or more selected from the group consisting of hydroxy, halogen, (C1-C20)alkyl, halo(C1-C20)alkyl, (C1-C20)alkoxy, nitro, cyano, -NR 21 R 22, (C1-C20) alkylcarbonyloxy, (C1-C20) alkylcarbonylamino, guanidino, -SO 2 -R 23, and -OSO 2 -R 24; R 21 and R 22 are independently of each other hydrogen, (C1-C20)alkylsulfonyl, or (C3-C20)cycloalkylsulfonyl; R 23 and R 24 are independently of each other (C1-C20)alkyl, halo(C1-C20)alkyl, or (C3-C20)cycloalkyl; R 2 is hydroxy, halogen, (C1-C20)alkylcarbonyloxy, or (C1-C20)alkylsulfonyloxy; the heterocycloalkyl or heteroaryl of R 1 and the heterocycloalkyl of R 11 to R 15 may be further substituted by one or more selected from the group consisting of (C1-C20)alkyl, (C3-C20)cycloalkyl, (C2-C20)alkenyl, amidino, (C1-C20)alkoxycarbonyl, hydroxy, hydroxy(C1-C20)alkyl, and di(C1-C20)alkylamino(C1-C20)alkyl; and the heterocycloalkyl and heteroaryl contains one or more heteroatoms selected from the group consisting of N, O and S, and the heterocycloalkyl is a saturated or unsaturated mono-, bi-, or spirocycle having a carbon atom or nitrogen atom in a ring as a binding site, or a solvate, stereoisomer, or pharmaceutically acceptable salt thereof, as an effective component, and a pharmaceutically acceptable carrier, and being used in combination of radioactive iodine. L is (C6-C20)arylene, (C3-C20)heteroarylene, or (C3-C20)fused heterocycle; R 1 is (C3-C20)heterocycloalkyl, (C3-C20)heteroaryl, - O-(CH 2) m -R 11, -(CH 2) m -R 12, -NH-(CH 2) m -R 13, -NHCO-(CH 2) n -R 14, or -SiR 16 R 17 -(CH 2) m -R 15; R 11 to R 15 are independently of one another (C3-C20)heterocycloalkyl; R 16 and R 17 are independently of each other (C1-C20)alkyl; m is an integer of 1 to 3; and n is an integer of 0 or 1; Ar is (C6-C20)aryl or (C3-C20)heteroaryl, in which the aryl or heteroaryl of Ar may be further substituted by one or more selected from the group consisting of hydroxy, halogen, (C1-C20)alkyl, halo(C1-C20)alkyl, (C1-C20)alkoxy, nitro, cyano, -NR 21 R 22, (C1-C20) alkylcarbonyloxy, (C1-C20) alkylcarbonylamino, guanidino, -SO 2 -R 23, and -OSO 2 -R 24; R 21 and R 22 are independently of each other hydrogen, (C1-C20)alkylsulfonyl, or (C3-C20)cycloalkylsulfonyl; R 23 and R 24 are independently of each other (C1-C20)alkyl, halo(C1-C20)alkyl, or (C3-C20)cycloalkyl; R 2 is hydroxy, halogen, (C1-C20)alkylcarbonyloxy, or (C1-C20)alkylsulfonyloxy; the heterocycloalkyl or heteroaryl of R 1 and the heterocycloalkyl of R 11 to R 15 may be further substituted by one or more selected from the group consisting of (C1-C20)alkyl, (C3-C20)cycloalkyl, (C2-C20)alkenyl, amidino, (C1-C20)alkoxycarbonyl, hydroxy, hydroxy(C1-C20)alkyl, and di(C1-C20)alkylamino(C1-C20)alkyl; and the heterocycloalkyl and heteroaryl contains one or more heteroatoms selected from the group consisting of N, O and S, and the heterocycloalkyl is a saturated or unsaturated mono-, bi-, or spirocycle having a carbon atom or nitrogen atom in a ring as a binding site,