The invention relates to the use of monoclonal antibodies that only recognise the O-acetylated form of the GD2 ganglioside, or fragments of said antibody, for the diagnosis and the treatment of cancers in which the cells express the O-acetylated GD2, said antibody or said fragment recognising the O-acetylated GD2 molecules expressed by the tumoral cells and not recognising the GD2 molecules expressed at the surface of the peripheral nerves, in order to increase the specificity of the diagnosis and reduce the toxicity of the treatments. The invention also relates to artificially modified antibodies advantageously used for treating and diagnosing cancers in which the cells express the O-acetylated GD2.