He says the next step is to find the best micro RNAs for identifying each type of cancer and see how early they can be detected.
"We haven't developed a final blood test for detecting prostate cancer, especially not at an early stage," says Tewari. "But what we are very excited about is that it's proved the concept, it's proved the idea that not only are micro RNAs present in the blood and stable there, but micro RNAs arising from tumors can get into the bloodstream… and actually do get into the blood stream at levels high enough that we can detect them, and it—in our minds—opens up the possibility that this concept or this approach might be applied not to just prostate cancer but other types of cancer."
The technology for detecting micro RNAs very sensitively is already well-established, such as amplifying—making many copies—of small amounts of genetic material, commonly done in DNA fingerprinting in criminal cases.
Tewari says that's a big advantage over strategies that seek to use proteins as early signals of cancer. "Although that's an important line of investigation, it has some limitations, and one of the limitations is that proteins are quite difficult to identify and to detect. It's of course very possible to do that, but it's a lot of work to figure out a way to even detect one protein in a very accurate manner," he says.
The team's further studies will not only screen for more and better micro RNAs to signal cancer, but also study their functions.
"It's very possible that the kinds of micro RNAs that are circulating in the blood might reflect something about the tumor which might tell us which treatments might work better than others," Tewari says.
And "the blood tests that we would love to find are... ones in which we're not only detecting the cancer, but also finding those micro RNAs which are involved in actually causing the cancer because those RNAs—it might... be possible to manipulate them in some way or treat the cancer even in some way, by treating the micro RNAs," he adds.
In addition, the researchers want to know what is making micro RNAs so stable in blood and tissues, and whether that is related to their role in cancer.
Tewari now believes that there will be cancer blood tests in his lifetime. "I don't know when that's going to be, and there's a lot of work ahead and a lot of challenges," he says. "But absolutely, that's the goal, and that's why we do what we do."
This research was published in PNAS www.pnas.org Online Early Edition the week of July 28 - August 1, 2008, and was funded by: Pacific Ovarian Cancer Research Consortium, National Cancer Institute, Pacific Northwest Prostate Cancer SPORE, Core Center of Excellence in Hematology and the Paul Allen Foundation for Medical Research.