Several studies have demonstrated that the serum of patients with cancer contains antibodies that react with a group of autoantigens denominated tumor-associated antigens (TAA). TAA can be detected prior to clinical diagnosis; thus, they would be ideal biomarkers for early detection of cancer, using only a few microliters of a patient's serum. In the current study, we used an immune proteomic approach, combining two-dimensional (2D) electrophoresis, Western blot, and matrix-associated laser desorption/ionization-mass spectrometry (MALDI-MS) methods to identify TAA in the sera of patients diagnosed with breast cancer. Sera were obtained from 36 newly diagnosed patients with stage II breast cancer and those from 36 healthy volunteers were evaluated for the presence of the TAA. Alpha 2HS-glycoprotein (AHSG) antibodies were detected in 33 of 36 patients with breast cancer (91.7%) and in only 3 of 36 healthy patients (controls, 8.3%). Sensitivity of detection of autoantibodies against AHSG in patients with breast cancer was 91.7%. AHSG was detected in cancer tissue by immunohistochemistry. Our results strongly suggest that the presence of serum autoantibodies against AHSG protein may be useful as serum biomarkers for early-stage breast cancer screening and minimally invasive diagnosis in Mexican populations. In the present study, 2D immunoblot analysis was used to make a screening in samples of sera from patients with a diagnosis of early-stage breast cancer, in order to identify some autoantibodies that react against TAA. Proteins identified in the present study, particularly alpha 2HS-glycoprotein (AHSG), might be useful as potential biomarkers for breast cancer in early stages for Mexican populations. Copyright © 2014 Elsevier B.V. All rights reserved.