How would you catch five shadowy operatives among the population of North Carolina, South Carolina and Florida? The presence of these agents could reveal an incoming invasion, so the stakes are high.
If doctors could find tumor cells in a patient’s blood, they could analyze those cells to figure out whether the cancer will spread and what drugs could treat it. In a study published this month in Small, Duke researchers demonstrated a new device that uses sound waves to separate these rogue cancer cells from blood cells.
Like the sound waves used for ultrasounds, these waves have too high a frequency for us to hear, said study lead author Mengxi Wu. As the blood cells pass through the sound wave field, the bigger ones fall into a separate stream.
The study first mixed cancer cells in with healthy blood to try the device, and captured over 86 percent of the rogue cells, which are generally larger than normal cells. They gave it a test drive with samples from prostate cancer patients and successfully isolated some tumor cells.
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Doctors could one day use this technology to perform “liquid biopsies” instead of surgery to find and cut out bits of tumors. Other techniques shake the cells or tack on identifying molecules to them, which change the cells and make analysis harder. The sound waves leave the rogue cells intact.
“Taking a biopsy of a tumor is more invasive, while getting blood is fairly straightforward,” said Zena Werb, a professor at University of California, San Francisco who was not involved with the study. “When you’re doing a biopsy, you’re tearing tumor cells out. You might end up with a lot of dead cells, which may decrease the viability of the other cells.”
Not every tumor sheds cells into the bloodstream, Werb said. And when a tumor does send these rogue cells out, you could count on one hand how many show up in a tube of blood. In contrast, 7.5 milliliters of blood contain around 37.5 million red blood cells and tens of thousands of white blood cells.
“Knowing if you have them is not a bad thing,” Werb said. “If you don’t have any cells in your circulation, then you don’t have cells on a walkabout trying to find homes in your peripheral tissue. If you do have them, getting them in a healthy state is a good thing.”
Researchers can culture, or grow, a handful of intact, healthy tumor cells into a larger sample. Once they have enough, in theory they can test different chemotherapy drugs on the tumor cells to predict the best treatment for a patient.
The device could also find clusters of tumor cells. These indicate a high chance that a tumor will mestastasize, or spread and form new tumors, Werb said.
Previous acoustic devices took hours to separate rogue cells from healthy blood, which decreased the chances of a successful culture. This new device can filter a vial of blood in one hour.
The study authors, who come from six universities in the U.S. and Singapore, will test samples of different types of cancer and further develop the device for clinical applications.
“Our aim is to develop a new technology,” Wu said. “But at this stage, we still have a long way until we can get it to market.”
Added Werb, "With ultrasound 40 years ago, you could see a blob, but now you can see a baby with some detail. As this develops, it will become more and more efficient and effective. Time will tell."