The PCR-based microsatellite analysis (A) and the genetic classification of gastric cancers (B). Representative autoradiographs of the samples that were examined by PCR-based microsatellite analysis (A) and the genetic classification of the intestinal-type and diffuse-type gastric cancers based on loss of heterozygosity (LOH) and microsatellite instability (MSI) (B). (A) The left gel electrophoresis shows high-frequency MSI at more than 40% of the 15 homozygous markers. The right gel electrophoresis shows high-level LOH involving chromosomes 3p, 4p, 5q, 9p, 13q, 17p and 18q. The normal (N) and corresponding tumor (T) DNAs are indicated above each allelic band. The asterisk indicates MSI and LOH. The genomic DNA microdissected from formalin-embedded paraffin-fixed tissue was amplified and labeled by [α-32P]dCTP in the hot start condition of multiplex PCR. A total of 80 microsatellite amplicons from each specimen were run simultaneously on two sequencing gels. (B) Using a panel of 40 microsatellite markers on eight cancer-associated chromosomes, LOH was interpreted at the heterozygous markers if 40% or less of the homozygous markers exhibited MSI. The extent of the chromosomal losses, as scored according to the number of LOH-positive chromosomes, was divided into high-level (LOH-H) and low-level (LOH-L) losses for both the intestinal-and diffuse-types. In cases of diffuse type gastric cancers, zero or one chromosomal loss was classified into the baseline-level (LOH-B).