Cancer is usually identified based on where in the body it is found — tumors in the breast are called breast cancer; those in the colon, colon cancer. In most patients, this approach works. However, a new study suggests that for one in 10 patients these current identification methods classify cancer types incorrectly.

Why is this important? Because proper classification is critical to the decision as to which types of treatment options will be most effective.

The study confirmed known differences between subtypes of breast cancer, and it also revealed a new and surprising finding about triple-negative breast cancer.

“It's only ten percent that were classified differently, but it matters a lot if you're one of those patients,” Josh Stuart, one of the authors and a professor of biomolecular engineering at UC Santa Cruz said in a statement.

Since certain types of cancer have more genetic variations, the actual rates of reclassification based on genetic signatures may be far higher.

Stuart and his colleagues have released a classification method based on molecular analysis of cancers rather their tissue-of-origin. The multi-institute research team compared samples from 12 different cancers across thousands of patients and was able to identify distinct genetic signatures. Cancer types were characterized using six different “platforms” or methods of molecular analysis.

In many cases, the identification of cancers using these platforms exactly matches the IDs based on tissue-of-origin. In some cases, there were differences.

Cancers originating in the bladder were particularly interesting. According to the findings, these cancers could be broken down into three main subtypes. One of these was bladder cancer only, but some samples had the signature of lung cancers, and others had a signature of “squamous-like” that may be associated with certain bladder, lung, or head-and-neck cancers.

“If you look at survival rates, the bladder cancers that clustered with other tumor types had a worse prognosis. So this is not just an academic exercise,” Stuart said.

The study confirmed known differences among subtypes of breast cancer, and it revealed a new and surprising finding about triple-negative breast cancer. These “basal-like” breast cancers actually are their own cancer type. They are especially aggressive and more prevalent among African-American and younger women.

“Even though these basal-like cancers arise in the breast, on the molecular level they have more in common with ovarian cancers and cancers of squamous cell origin than to other subtypes of breast cancer,” Christina Yau, co-lead author of the study explained.

The new approach to cancer classification stands to advance drug development and clinical trials of cancer drugs. Reclassification of cancer types would allow patients to benefit from therapies that are more tailored to their specific needs — a major step towards improving outcomes for cancer patients.

The researchers say that although follow-up studies are needed to validate and refine this newly-proposed classification system, the goal is that it will ultimately provide the foundation for a better kind of personalized cancer treatment.

The study is published in the journal Cell.