Blog | Monday, April 25, 2011

Breast cancer complexity in personalized medicine

Scientists at Washington University School of Medicine in St. Louis have conducted the single largest cancer genomics investigation to date by sequencing the entire genomes of tumor from 50 breast cancer patients. They compared the cancer DNA to healthy cells in the same patient and found mutations that only occurred in the cancer cells. They uncovered incredible complexity in the cancer genomes of these tumors that had more than 1,700 mutations, most of which were unique to the individual.

To undertake this study, the oncologists and pathologists worked with the University's Genome Institute to sequence more than 10 trillion chemical bases of DNA, repeating the sequencing of each patient's tumor and healthy DNA about 30 times to ensure accurate data. Huge computing facilities were required to analyze this amount of data. All patients in the trial had estrogen receptor positive breast cancer.

The researchers found that two mutations were relatively common in many of the patient's cancers. One is present in about 40% of estrogen positive breast cancer and the other present in about 20%. They found a third mutation that controls programmed cell death and is disabled in about 10% of estrogen-receptor-positive cancers. This mutated gene allows cells that should die to continue living. Only two other genes had mutations that recurred at the 10% level.

They found 21 genes that also significantly mutated, but at much lower rates. Even though these mutations were relatively rare, they still involve thousands of women and are very important to understand.

These highly detailed genome maps are an important first step to designing therapy that is personalized to the patient. We do not know why treatment works for some women and not others. It may also help us understand aggressive types of breast cancer that are difficult to treat and occur in young women and African-American women.

Individual and personalized medicine is only possible when the cancer's genetics are known in advance. We are getting closer each day.

This post originally appeared at Everything Health. Toni Brayer, FACP, is an ACP Internist editorial board member who blogs at EverythingHealth, designed to address the rapid changes in science, medicine, health and healing in the 21st Century.