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Although the laser is still far from becoming a commercial diagnostic tool, it is up to 1000 times more sensitive than current methods of detecting tumor cells in the blood, researchers said in the journal Science Translational Medicine, LiveScience.
To test the spread of cancer, doctors usually take blood samples, but tests often fail to detect tumor cells, even if they are present in a single sample, especially if the patient has an early form of cancer, said senior author Vladimir Zharov, director of the nanomedicine center of the University of Arkansas for medical sciences.
If the tests are positive, it usually means that the blood contains a high concentration of circulating tumor cells. At this point, the cancer has probably spread to other organs and is often "too late to effectively treat patients," Zharov added. [Top 10 Cancer-Fighting Foods]
Years ago, Zharov and his team had the idea of a non-invasive alternative method for testing larger amounts of blood with greater sensitivity. Taking the usual route, they tested it in the laboratory, then on animals and recently conducted it in human clinical trials.
The new technology, dubbed the Cytophone, uses pulses of laser light on the outside of the skin to heat the cells in the blood. But the laser only warms melanoma cells, not healthy cells, because they contain a dark pigment called melanin, which absorbs light. The Cytophone then uses an ultrasound technique to detect the very small waves emitted by this heating effect.
They tested the technology on 28 clear skin patients with melanoma and 19 healthy volunteers with no melanoma. They projected the laser onto the patients' hands and found that in the space of 10 seconds to 60 minutes, the technology could identify circulating tumor cells in 27 of the 28 volunteers.
Find and kill tumor cells
The device gave no false positive results on healthy volunteers and did not cause safety problems or side effects, they said. Melanin is a pigment normally found in the skin, but skin cells are not damaged, Zharov said. Even though the skin naturally produces melanin, this laser technique does not harm these cells. This is because the laser light is scattered over a large area of the skin (so it is not focused enough on the skin cells to damage them).
Unexpectedly, the team also found that after treatment, cancer patients had fewer circulating tumor cells. "We used relatively low energy" for the main purpose of diagnosing cancer rather than treating it, Zharov said. Yet even at this low energy, the laser beam seemed to destroy the cancer cells.
Here's how it works: As melanin absorbs heat, the water around the melanin in the cells begins to evaporate, producing a bubble that expands and collapses, mechanically destroying the cell, Zharov explained.
"Our goal is to kill these cells, we can help prevent the spread of metastatic cancer," he said. But he hopes to conduct more research to optimize the device to kill more tumor cells, while remaining harmless to other cells.
In addition, they have not yet tested the device on people with darker skin and higher levels of melanin. Nevertheless, only a very small percentage of African-Americans contract melanoma.
The team hopes to extend its technology in search of circulating tumor cells, released by cancers other than melanoma. These cancer cells do not carry melanin. To detect them, researchers must first inject patients with markers or specific molecules that bind to these cells so that they can be targeted by the laser. They have so far shown that this technique can work on human bad cancer cells in the laboratory.
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