The immunological screening of breast cancer was performed with IgG autoantibodies by the serological analysis of recombinant cDNA expression library methods to explore novel tumor associated antigens. We have focused on a small zinc finger protein metallopanstimulin-1 (MPS-1). MPS-1 mRNA was ubiquitously expressed in normal human tissues except the brain and the placenta. In Western blot analysis, MPS-1 was easily detected strongly in actively proliferating cells and three breast cancer cell lines. In the tissue the protein of MPS-1 in cancer cells was more abundant than that of surrounding normal cells. Screening of tissue specimens by immunohistochemistry revealed 50.4% positive for MPS-1 in 125 cancer patients. These data suggest that MPS-1 could be applicable to the immunotherapy of breast cancer.