[Identification of the target molecule of autoantibodies in acquired autoimmune hemolytic anemia]

The incidence of autoimmune hemolytic anemia (AIHA) after a solid tumor is commonly lower than that of AIHA secondary to collagen and lymphoproliferative diseases. In addition, a solid tumor has not been considered a cause of macrocytic anemia. However, recent studies in Japan have reported that several solid cancers are complicated by these conditions. Previously, we have reported a case of AIHA complicated by colorectal cancer ectopically expressing band 3, an anion transporter protein that is restrictedly expressed in erythrocytes and renal cells. Subsequently, a prospective study was performed to analyze the frequency of band 3 expression in the colorectal cancer cells of 50 patients and the level of IgG binding on erythrocytes relative to that in healthy controls. Results showed that an increase in antiband 3 antibody in the serum and erythrocyte membranes could cause normocytic anemia. The current study evaluated the mechanism that induces the ectopic expression of band 3 and that increases the antigenicity on erythrocytes, leading to a shorter erythrocyte life span in cancer patients, based on previous reports about band 3 and our own clinical and laboratory studies. The current study indicates that this phenomenon can be a major cause of cancer-related anemia.