Use of pretreatment serum CA9 (carbonic anhydrase 9) to predict PFS and survival in trastuzumab-treated metastatic breast cancer

11092 Background: Approximately half of HER2-positive breast cancer patients will respond to first-line trastuzumab-containing therapy. However, in those patients with an initial trastuzumab response, most will progress within a year with acquired resistance. Since trastuzumab treatment is also now used in the HER2-positive adjuvant breast cancer setting, trastuzumab resistance will continue to be a vexing clinical problem, and better predictive and prognostic biomarkers are urgently needed. Methods: Serum HER2, tissue inhibitor of metalloproteinase-1 (TIMP-1), urokinase-type plasminogen activator (uPA), CA9, VEGF-165, and endoglin were measured using ELISA assays in 66 metastatic breast cancer patients before starting first-line trastuzumab-containing therapy. The HER2, TIMP-1, uPA, CA9, and VEGF-165 ELISAs were from Oncogene Science/Siemens Healthcare Diagnostics, Cambridge, MA; and the endoglin ELISA was from R&D Systems, Minneapolis, MN. Progression-free (PFS) and overall survival (OS) were analyzed u...