Evaluation of soluble CD44v6 as a potential serum marker for head and necksquamous cell carcinoma

In recent years, the measurement of soluble CD44 Levels in the circulation of patients with malignant diseases has been introduced as a new and simple diagnostic tool for the detection of human cancer. The high CD44v6 express ion in head and neck squamous cell carcinoma (HNSCC) would enable the use o f soluble CD44v6 proteins present in the circulation of HNSCC patients as a marker of disease, In the present study, we determined CD44v6 plasma level s using a domain-specific ELISA in healthy volunteers, non-cancer patients, and HNSCC patients before and after surgical removal of the tumor, A diffe rence between the CD44v6 plasma levels of HNSCC patients and controls could not be observed, Moreover, surgical removal of the tumor did not result in a reduction of the CD44v6 plasma level in the HNSCC patients. In addition, the spectrum of soluble v6-containing CD44 proteins present in the plasma of HNSCC patients and controls was determined by immunoprecipitation experi ments, but again, tumor-related isoforms could not be distinguished in pati ent samples. Additional experiments to unravel the biological source of these circulatin g proteins indicated surprisingly that the v6-containing proteins present i n the circulation of healthy individuals are only released in part, if at a ll, by activated lymphocytes or other nucleated blood cells. Most circulati ng CD44v6 proteins seem to be derived from the normal epithelial cell compa rtments, including breast cells, colon cells, and squamous cells. Taken tog ether, these data do not support the use of soluble CD44v6 as a tumor marke r in HNSCC or any Ether tumor type that has developed from tissues producin g soluble isoforms.