This invention relates to α1-microglobulin (A1M) for use in the diagnosis or treatment of malignancies requiring radionuclide diagnostics (RD), radionuclide therapy (RNT) or radioimmunotherapy (RIT), respectively, wherein A1M is used as a co-treatment to RD, RNT or RIT.本發明是有關分別用於診斷或治療需要放射性核種診斷法(RD)、放射性核種治療(RTN)或放射性免疫治療(RIT)的惡性病中之α1-微球蛋白(A1M),其中A1M用作為RD、RNT或RIT的共同治療。