A new study of the protein-coding genes in 100 breast cancer tumors revealed vast differences among the cancers and highlights how complicated the disease really is, researchers said Wednesday.

A sobering perspective on the complexity and diversity of the disease is emerging, they wrote in the online edition of the journal Nature (subscription required), which is publishing a series of studies of the genetic changes in breast cancer.

The scientists, led by Michael Stratton at the Wellcome Trust Sanger Institute in Hinxton, England, found 73 different combinations of disease-causing mutations in the tumors, each involving up to six different genes from a set of 40 driver genes.

Seven of the 40 individual driver genes were mutated in more than 10% of cases, but 33 others that were less common also contributed to the development of the cancers, the team reported. In 28 cases, a single mutation was enough to cause disease.

The researchers identified nine new genes that caused the cancers, and also found mutations in genes that were already known to cause breast and other cancers.

Discovering that a single disease breast cancer can appear in so many different guises means that developing targeted therapies tailored to a patients tumor type will remain a tall order in the near future.

The situation is more complex than anyone would like to see, said Christina Curtis, an assistant professor of preventive medicine at the Keck School of Medicine at USC and first author of another paper in Nature, released in April, that detailed several new breast cancer subcategories.

But it seems were getting closer, Curtis added. With each study were getting a new vantage point.

Curtis said that finding new driver genes and new combinations of driver genes could still eventually pave the way to new treatment options, once researchers dig further and figure out exactly how the different combinations of mutations change cellular function, causing cancer.

Her team at USC is working on techniques to examine mutations in single cells, which will let scientists study genetic variation within tumors as well as between then.

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Breast cancer study reveals 'substantial genetic diversity'