Cancer-related chromosomal aberrations

Visible changes in the structure of chromosomes in cancer cells provide direct evidence for the genetic basis of cancer. Rearrangements at many definite positions have been observed repeatedly in many types of cancers . At the molecular level are found miscoding changes, including substitutions, deletions, duplications, and rearrangements of DNA building blocks. For example, in a recent study of breast and colon cancers, 189 genes (average 11 per tumor) were frequently found to be mutated. In several cancers, mutations change the functioning of genes located at their positions. DNA is often altered in human chromosome 6 at position p21, where the cancer-related K-ras oncogene, a gene that may modify cell growth aberrantly and lead to cancer, is located. Additional copies of a particular gene make a cell resistant to the anticancer drug methotrexate. Rare cancers are produced by virus infection; for example, introduction of genetic material by the human papilloma virus causes cervical cancers. This provides further evidence for the genetic basis of cancer.