While we tend to think of cancer as a single illness, it's really many diseases and within specific types of cancer, there are often multiple subtypes. For example, while all breast cancers are due to changes in the DNA of breast tissue, there are several varieties of breast cancer and each generally responds better to a somewhat different treatment program.
By breaking cancer into smaller and smaller subgroups based on patients' DNA profiles, oncologists can better predict which treatment options are likely to be most effective and how well each patient will do. This is the basis of personalized cancer treatment.
DNA
All cancers begin with mutations in the DNA of one cell. Individuals inherit a small percentage of mutations; the rest usually arise from environmental factors. DNA (Deoxyribonucleic Acid) is a molecule inside cells that stores millions of bits of information. Despite its tiny size, DNA carries the entire set of genetic instructions for an individual.
DNA is made of repeating parts called nucleotides, which are arranged in a specific sequence. Mutations can change a single nucleotide or change the DNA sequence. This disrupts the cell's normal life cycle, and, as a result, mutated cells may accumulate and create a tumor mass. Usually, it's the accumulation of mutations that transforms a normal cell into a cancerous one.
Personalized cancer treatments
According to Gordon B. Mills, M.D., Ph.D. at the MD Anderson Cancer Center, oncologists traditionally treated patients based on where their tumor started (breast, prostate, colon). However, patients with the same type of tumors responded differently (or not at all) to the same treatments. Unfortunately, they had no way of knowing beforehand how any individual patient might respond.
Instead, personalized cancer treatments are based on the genetics of each individual. For example, scientists at the Genome Institute have identified distinct signatures in advanced breast cancer that might predict which women are most likely to benefit from estrogen-lowering therapies. This knowledge will hopefully improve the prognosis for some women and spare others for whom estrogen-based treatments will not be effective. In early clinical trials, researchers also found that women who respond to estrogen-lowering therapies tend to have fewer, and less complex, mutations than women who didn't respond.
This growing body of knowledge will make it possible for oncologists to tailor the dose and frequency of chemotherapy drugs for individual patients and understand how toxic a treatment option might be. It also gives cancer researchers specific targets for potential new drugs or alternative ways to use existing drugs.
Sources:
The Genome Institute at Washington University. "Decoding DNA Finds Breast Tumor Signatures That Predict Response." Web. http://genome.wustl.edu/highlights/article/decoding_dna_finds_breast_tumor_signatures_that_predict_treatment_response/
Mills, Gordon, M.D., Ph.D. "Personalized Medicine for Breast and Ovarian Cancer." MD Anderson Cancer Center. Webcast. Web. 17 June 2008. http://www.mdanderson.org/publications/patient-power/episodes/2008/breast-and-ovarian-cancer-treatment-podcast.html
Inside Cancer. "Hallmarks of Cancer." Web.
http://www.insidecancer.org/
DNA Sequencing. "DNA." Web.
http://dnasequencing.com/DNA.html
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Genomics of Breast Cancer
http://genome.wustl.edu/projects/cancer_genomics/genomics_of_breast_cancer
