To determine whether elevated circulating Hsp70 and Hsp90 are responsible for the catabolic activity of tumor cells, we treated primary rat and C2C12 myotubes with conditioned medium of LLC (LCM) or C26 (CCM) cells with or without the inclusion of neutralizing antibody against Hsp70 and/or Hsp90, and monitored levels of E3 ligases atrogin1 and UBR2. This evidence concerns the gene HSP90AB1 and neoplasm.