A group of scientists has uncovered a startling truth about an especially deadly form of breast cancer: turns out, it's actually a lot of different kinds of breast cancer.

Triple-negative breast cancer accounts for 16 percent of breast cancer diagnoses and about 25 percent of breast cancer deaths. To date, it has been defined solely by what it lacks: the surfaces of its cells do not have receptors for the hormone estrogen or the steroid progesterone, which are linked to breast cancer. Triple-negative breast cancer cells also do not have HER2 receptors, which are targeted by the breast cancer medicine herceptin.

That means that triple-negative breast cancer can evade all sorts of modern treatments that target various cell surface receptors, and patients often have to run the gamut of other therapies - surgery, chemotherapy, and radiation - to stand a fighting chance.

In a study published in the journal Nature on Wednesday, researchers led by a team from the University of British Columbia conducted a genetic analysis of cancer cells taken from 104 patients with triple-negative breast cancer. They found that no two genomes were similar.

At the moment, we're treating all of these like they're the same cancer, but clearly that's not the case, says UBC researcher Samuel Aparicio, the senior author of the study.

Aparicio drew a parallel between the different triple-negative breast cancer types and the variety of species found within an ecosystem: some cancers have one or two kinds of malignant cells, while others have many different kinds. Whatever therapies are given to patients can't just target one species and allow the others to flourish.

He compares the situation to the one facing researchers racing to find treatments for HIV, which did not have a successful treatment for many years. Then, around the turn of the century, researchers realized that they could combine three kinds of therapies to prevent the virus from mutating.

More effective treatments will come as scientists are better able to identify the genetic features of a patient's tumor, the researchers say.

In a statement, Aparicio said the findings present a unique opportunity to design clinical trials for patients with triple negative breast cancer.

We can explore patient responses to treatment at the genetic level and look at ways to improve therapies and outcomes for patients, he said.

Clarification: An earlier version of this story said that herceptin was merely linked to breast cancer. The story has been modified to reflect that it is a medicine that targets HER2 receptors.

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