The main difficulty of description of particle excess in cosmic rays  with
unstable dark matter is the restriction given by isotropic gamma-ray background
(IGRB) [2-4]. The final-state radiation (FSR) from the DM decay or annihilation
process makes major contribution to the gamma-ray flux in these models. There are models where decay goes through cascades with some intermediate particles. In this work we study the FSR output from such cascade in dependence of the mass of intermediate particle in the search for its possible suppression.