Mike Lewis and Don Buck both have prostate cancer. Doctors told Lewis to watch his tumor, but wait on treatment.

"He said that in the meantime I’m looking at this as something that [I'll] probably die with, and not of," Lewis said.

Buck's cancer, however, became aggressive.

"I had my prostate removed," he said.

Dr. Eric Klein said these kinds of patients are difficult to identify at diagnosis, however, there's now a new way called genomics. First, patients have a biopsy. Then, the test measures which genes are in the tumor.

"We can tell from that little amount of cancer how aggressive the cancer is," said Klein, urologist, Cleveland Clinic, Ohio.

As many as half of all prostate cancers in the United States are low-risk. About 100,000 men in this category undergo treatment, even though there's only a three-percent chance their disease will progress or become life-threatening.

"We now have the capacity to more accurately look someone in the eye and say, 'Yeah, you do have a cancer, but it isn't anything to worry about,'" Klein explained.

It's a simple test that could save a life or spare a patient from harsh therapies.

This same method has been used for years to help predict if chemotherapy is necessary for breast cancer patients who undergo surgery. Klein said he believes there will one day be a similar test for all types of cancer.

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