The present invention relates to a composition comprising a first gRNA bound to an RNA-guided endonuclease forming a first ribonucleoprotein complex, said first gRNA comprises a first targeting sequence being complementary for a first target sequence in an intron in the 5′ upstream part of a fusion gene; and a second gRNA bound to an RNA-guided endonuclease forming a second ribonucleoprotein complex, said second gRNA comprises a second targeting sequence being complementary for second target sequence in an intron in the 3′ downstream part of the fusion gene. Such compositions may find use in the treatment of fusion gene related cancers.