Chromosomal and enzymatic patterns provide evidence for two types of human colon cancers with abnormal nucleotide...

Correlated chromosomal and enzymatic studies are reported in a series of 13 human colon cancers. Two distinct chromosomal patterns are found: one with many losses, called monosomic type and another with many gains, called trisomic type. Chromosome 18, which carries the gene for thymidylate synthase (TS) is always missing in the monosomic type, in which TS activity is low. On the contrary, TS activity is high in the trisomic type on the average. The long arm of chromosome 17, which carries the gene for thymidine kinase (TK), is frequently duplicated in both monosomic and trisomic types, in which TK activities are high. It is found that most other deletions affect chromosomes carrying genes for enzymes of the de novo pathways whereas most other gains affect chromosomes carrying genes for enzymes of salvage pathways for synthesis of nucleotides. The importance of this finding is discussed.