All tumor samples will be reassessed for confirmation of diagnosis by a pathologist. For each patient, paraffin blocks with both tumor tissue and normal mucosa will be selected for DNA extraction and polymerase chain reaction at microsatellite targets. The tissues were routinely collected from the operating room, fixed in buffered formalin, embedded in paraffin, and stored for a variable number of months prior to selection for analysis. Paraffin-embedded blocks will be cut with a microtome into 20-µm thick sections. Using a sterile scalpel blade, areas of normal (non-tumor) and cancer tissue will be microdissected under a dissecting microscope utilizing a haematoxylin and eosin-stained section as a guide. The specimens will be deparaffinised in toluol, purified with absolute ethanol, and centrifuged at 14,000 rpm. Previous experience in Dr Hutter's laboratory has demonstrated that it is indeed technically possible to perform this type of molecular analysis in paraffin-embedded tumour specimen.