SAN FRANCISCO, Dec. 19 (Xinhua) -- A new study led by researchers at the Stanford University School of Medicine indicates that profiling the genes of lung-tumor cells from patient blood samples may be a cheap, noninvasive way to help doctors choose the right treatments.
The researchers created a system for isolating circulating tumor cells from the blood of cancer patients and reading a handful of genes from inside each tumor cell, enabling them to obtain genetic information about the original cancer tumor that resides deep in the lungs without doing a biopsy, which can be dangerous for the patient.
It is common for cancer therapies to fail after a few months, often because the cancer evolves resistance to the treatment. At that point, "without a biopsy and genetic profiling, we are flying blind, trying to select a second or third option for therapy and hoping it works," said radiology instructor Seung-min Park, a lead author of the study published online in the Proceedings of the National Academy of Sciences. But repeated lung biopsies are too hard on patients.
Finding a way to look at circulating tumor cells, or CTCs, in the blood has been a goal of oncologists for years. When people die of cancer, it is usually from metastasis, the spread of tumors throughout the body. Part of metastasis is the entry of tumor cells into the bloodstream, where they circulate along with normal blood cells, eventually landing in other organs and initiating tumors there.
"This work fits well into our bigger vision of using blood-based diagnostics to detect and manage disease, including cancer," said Sanjiv "Sam" Gambhir, professor and chair of radiology. "By being able to characterize single CTCs, we believe cancer management, including predicting response to therapy, will be much better optimized."
The blood typically contains very few CTCs, so one of the challenges has been to separate them from ordinary blood cells. The new technique involves taking blood from lung cancer patients and then attaching antibodies to circulating tumor cells. Once the cancer cells are labeled, the team introduces magnetic nanoparticles designed to attach to the antibodies labeling the cancer cells.
With each individual cancer cell labeled with a magnetic nanoparticle, the researchers can then use a device called a magnetic sifter, or MagSifter, previously developed by Shan Wang, Stanford professor of materials science and engineering and of electrical engineering.
When the MagSifter is on, it pulls the nanoparticle-labeled CTCs from the blood sample and allows the rest of the blood to flow through the sifter. The CTCs pulled from the blood are then deposited into a flat array of tiny wells, each large enough for only one cell. Now the tumor cells are ready for genetic analysis.
In principle, the technique should work just as well with other kinds of cancers, said former Stanford graduate students Dawson Wong. "We validated our device on lung cancer because of the difficulties of doing lung biopsies," he was quoted as saying in a news release. "But the technology is not limited to profiling lung cancer. We could swap out markers and adapt the technique to other types of cancers."
The approach could be used to look at mutations in three or four genes, and it requires no more than 2 milliliters of blood, or about half a teaspoon. The test can be completed in about five hours, the researcher said, and costs less than 30 U.S. dollars.