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Monday, April 25, 2011

Sequencing breast cancer


Matthew Ellis from the Washington University School of Medicine led a team of geneticists and oncologists in sequencing the entire genomes of 50 different breast cancer tumors. The new data will allow doctors to not only categorize types of breast cancer, but also perhaps to personalize treatment.

In order to specifically identify the gene changes that were unique to the cancers, the scientists compared the DNA in the tumors to the DNA of the same patients’ healthy cells. That way, exact genetic comparisons could be made between healthy tissue and cancerous tissue within each person. Considering that each genome was sequenced 30 times to ensure accuracy, the entire project required the sequencing of over 10 trillion base pairs.

In all there were over 1700 mutations in the tumor genomes, though many may not have been specifically related to the cancer. Only five mutations were each found in over 10% of the tumors, and one of them was present in 40% of the tumors (some tumors had more than one of these common mutations). Of course, a gene disruption that is only found in one woman out of 50 may still be responsible for thousands of cases of breast cancer in the general public, or may be more common in other types of cancer.

Only women with estrogen-receptor-positive breast cancer were recruited for this study. Although all were given estrogen-lowering drugs in an attempt to slow their tumor growth, only about half the women responded to this treatment. The scientists are hopeful that among other things, this study will help doctors figure out when to offer specific treatment regiments like estrogen suppression.

Caption: The above Circos plot is a visual representation of the genomic disruptions in one of the breast cancers studied.

Credit: Matthew J. Ellis, MD, PhD