RESUMO
BACKGROUND: Tumor invasion occurs following enzymatic degradation of components of the extracellular matrix. The proteolysis-resistant domains of matrix components are likely to appear in the blood plasma during invasion, and could be used as markers of malignancy. Cellular fibronectin (cFN), a major ECM component, possesses 3 alternately spliced principal protease resistant domains; two of which, extra domain A (EDA) and III connecting segment (IIICS), were selected for this study of the nature of the plasma cFN molecules and its levels in normal subjects (n=51), and patients with gastrointestinal (G-I, n=145) or head and neck (H-N, n=127) cancers. METHODS: ELISA was used to measure the cFN levels in plasma and Western blotting to analyze its fragmented nature in plasma samples from normal individuals and patients with G-I or H-N cancers. RESULTS: cFN in blood plasma, as probed by anti-EDA and anti-IIICS antibodies on Western blots, is found to exist entirely in a fragmented form in normal subjects and G-I and H-N cancer patients. The cFN polypeptides in plasma have Mr of 160 and 100. The levels of plasma cFN, determined by ELISA using the 2 antibodies, are found to be increased in G-I and H-N cancers. In a significant number of stomach (43%), gall bladder (35%) and colon (17%) cancer cases an additional anti-EDA-reactive 30 kD peptide is seen in the plasma. CONCLUSIONS: The mean rise for all sites is statistically significant, and 65% of all patients show cFN levels >80th percentile of normal values. The characterization of the 30 kD peptide showed that it does not contain the IIICS domain and also lacks the central cell- and heparin-binding sites.