“…Two variants of this tumor have been previously reported as W256 A and B (Guaitani et al, 1982), which are currently known by their growth capacity and lethality after subcutaneous (sc) injection in Wistar rats. This lethality is associated to the severe homeostatic disturbances induced by the W256 tumor, which includes anorexia (Rettori et al, 1995;Guaitani et al, 1982), anemia (Zucker et al, 1977;Vido et al, 2000), thymus atrophy (Rettori et al, 1995) and hydro electrolyte disturbances with glomerular filtration and tubular function alterations (Toal et al, 1960;Morrison, 1971;Rettori et al, 1995;Guimarães et al, 1999;Rettori et al, 2000). Nevertheless, spontaneous W256 tumor regression can occur.…”