Ectopic expression of band 3 anion transport protein in colorectal cancer revealed in an autoimmune hemolytic anemia patient.

Cancer patients occasionally have anemia with high mean corpuscular volume in addition to iron deficiency anemia. Secondary autoimmune hemolytic anemia (AIHA) following cancer is also observed with low frequency. To date, no causal mechanisms for these disease states have been reported. Here, we present the case of an 80-year-old woman with AIHA that was resistant to prednisolone. Further examinations revealed primary adenocarcinoma of the sigmoid colon and primary squamous cell carcinoma in the right lung. After resections of these tumors, her anemia partially improved until a colon cancer–derived metastatic tumor was detected in the left lung. Immunoprecipitation of erythrocyte membrane proteins with an autoantibody followed by mass spectrometry/Western blotting identified band 3 as the target of the autoantibody. Immunohistochemical analysis revealed ectopic expression of band 3 in the colon adenocarcinoma. To our knowledge, this is the first report that identifies the cause in a case of anemia without bleeding in a cancer patient and that defines a mechanism underlying secondary AIHA following cancer progression.