Serum proteome analysis for profiling protein markers associated with lymph node metastasis in colorectal carcinoma.

Colorectal cancer (CRC) is the second leading cause of cancer death in the human population worldwide. In China, CRC ranks fifth among cancer deaths, with a continuous increase in the incidence. Most CRC patients have lymph node metastasis (LNM) when first diagnosed. Two-dimensional (2D) serum proteome analysis may be useful in discovering new biomarkers that may aid in the diagnosis and therapy of CRC patients. To determine the tumour metastasis-specific antigen markers of CRC metastasis, sera from 32 patients with non-LNM CRC and 40 patients with LNM CRC were selected for screening using 2D serum proteome analysis combined with mass spectrometry (MS). Pretreatment strategies, including sonication and depletion of albumin and immunoglobulin (Ig) G, were adopted for screening differentially expressed proteins of low abundance in serum. By 2D image analysis and Matrix-assisted laser desorption/ionisation-time of flight (MALDI-TOF)-MS identification, eight protein spots were differentially expressed and successfully identified. The molecule transthyretin (TTR) was further studied in these sera by enzyme-linked immunosorbent assay. TTR appears to be a potential CRC metastasis-specific serum biomarker, which may be of value in the clinical detection and management of CRC.