Loss of the long arm of chromosome 18 (18q) is one of the most common genetic changes in colorectal cancer. This chapter describes the method to determine chromosome 18q status using microsatellite markers. Specifically, tumor and normal tissue are separated by microdissection of routine formalinfixed paraffin embedded tissues obtained from surgical resection. Total genomic DNA are isolated and subjected to polymerase chain reaction (PCR) using polymorphic microsatellite markers located on the long arm of chromosome 18 (1 ).
