This study is designed to gain an understanding of how a single intravenous infusion of LV affects the folate concentration in blood, tumor and adjacent mucosa tissue. By using the LC/MS method which was recently developed and it is now possible to quantitate the different metabolites of LV in small tissue samples as well as in blood. It is further now possible to measure by quantitative Polymerase Chain Reaction techniques (PCR) the most important genes involved in the folate transport and metabolism ((SHMT1), SerineHydroxyMethylTransferase1 and (ABCC3) ATP-binding cassette, sub-family C, (CFTR/MRP), member 3)).