The Human Genome Project has provided not only information about the human genome, but has been responsible for the refinement of the techniques available to scientists to do genetic study. Many of these techniques are applicable to research into cancers and cancerous cells.

A feature common to many cancers is chromosome rearrangement, in which an "arm" of one chromosome trades places with the arm of another. Another feature is presence of abnormal gene copies. For example, more than 30 different regions of such abnormal copies have been found in breast cancer cells. Some of these abnormalities are common to other cancer types, as well. Within these repetitive areas can be found oncogenes (genes that induce cancers), tumor suppressor genes, and genes that predispose an individual to develop specific cancers. Some of these genes include MYC, AKT2, p53, BRCA1 and BRCA2.

Researchers have observed that as a person's cancer progresses through various stages, the genetic abnormalities also increase. The genetic mutations found in a primary tumor are carried by the metastatic tumors that arise from it. Occasionally, a cancer patient will develop evidence of cancer in a site other than the primary site, and a question arises as to whether that new tumor is a metastasis from the original or a second cancer. Genetic analysis of the second tumor can reveal that information, which may guide physicians in determining the best treatment.

The genes BRCA1 and BRCA2 predispose women to developing breast cancer, but sporadic breast cancer arises in women without either gene. Those women who carry the BRCA mutations have more genetic abnormalities in their breast cancer cells than women with sporadic breast cancer. Prostate cancer in African-American men is more likely to demonstrate certain genetic abnormalities than that found in white men, which might be a contributing factor in the increased incidence of prostate cancer among African-Americans.

A number of studies have shown that certain genetic abnormalities are associated with better or worse prognoses for patients with cancer. Genetic profiling of cancer patients may offer opportunities to tailor treatments, choosing drugs that are most likely to be effective with particular genetic profiles.