By scanning the DNA of tumor cells, researchers have found evidence of far more gene mutations than previously suspected. In one family of genes taken from 200 samples of breast, stomach, colorectal and other common tumors, the researchers found more than 1,000 different mutations.

Of those mutations, 120 are believed to be "driver" mutations that directly contribute to cancer development. These mutations "drive" a cell to stop behaving normally and to behave like cancer cells.

The family of genes studied are called kinases, which are the basis of some of the targeted therapies that have shown promising results in a small number of cancer patients. The reasons for the mutations are largely unclear, though lung cancer mutations, for instance, result from years of smoking damage. Lung cancers had the most mutations, followed by gastric cancers, ovarian cancers and colorectal cancers. Testicular cancer tumors and most breast cancers had few mutations.