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Bob Roehr is a medical writer based in Washinton, D.C.
Columbia, Mo. - Imagine that metastasizing melanoma cells in circulating blood can be identified by the sound that they make.
That is exactly what John Viator, Ph.D., did in combining laser, optic and ultrasound techniques to create a unique diagnostic for the deadly cancer.
His technique uses a centrifuge to separate lymphocytes and any possible circulating melanoma cells from a blood sample. That mixture is forced through a flow chamber where it is zapped with quick pulses from a blue laser.
But the laser waves affect melanoma cells very differently; the pigment expands and contracts with each pulse of energy, generating tiny shock waves of high-frequency ultrasound within the sample.
"We can detect that difference with a very small, sensitive acoustic sensor in the flow chamber," he tells Dermatology Times.
More cells, more 'noise'
Dr. Viator is developing the diagnostic with colleagues at the University of Missouri, Columbia.
The work to date has been with cultures of human melanoma cells mixed with various ratios of white blood cells. The results appear in the Oct. 15 issue of the journal Optics Letters.
Dr. Viator has found a dose-response curve, in which - as expected - a greater number of melanoma cells correlates with a greater volume of generated noise.
"The acoustic wave strength tells you if there is zero, a few or a lot of melanoma cells present; it will give you the relative number," though the full meaning of those numbers is not yet known, he says.
Sensitivity has been pushed down to as few as 10 cells in the solution, and researchers are working to push it lower, down to detection of a single cell. Dr. Viator says the screening test can work with as little as 10 cc to 20 cc of blood. But, as always when trying to measure a substance present as only a very tiny fraction of the whole, a larger sample increases the likelihood of identifying the target.
"The whole science of circulating tumor cells is still unclear," he says. "How many there are? Are they always there if you are metastatic?"
He says that presumably is less of an issue in patients with advanced metastasized disease, who likely are shedding relatively larger numbers of cells, than in patients in earlier stages of disease, who likely are shedding fewer cells. That is where researchers will begin the clinical work.
Pilot study planned
Dr. Viator hopes to conduct a pilot study this year to determine "the incidence of circulating tumor cells for any given metastatic patient," and to use that information to plan a full-scale clinical trial in advanced metastatic patients that would begin in 2007.
He says the advantages of the photoacoustic approach are its simplicity - a marketed product would require no expertise other than in drawing blood - and its speed. It can be done in 30 minutes or less.
"With this screening, you may be able to do fairly regular monitoring of a patient with melanoma, every week or every month," he says. "If you don't see any circulating cells, it may be a good indication that the therapy has worked. Or if we do find circulating cells, it may be an indication that the treatment should be modified."
Dr. Viator says the mechanical components that would be used to put together this type of photoacoustic device for sale would not be tremendously expensive.
"It definitely would be cheaper than a really nice ultrasound machine," he says.
He hopes such a device would be affordable enough for an oncology clinic, eliminating the need for samples to be sent to a regional or national lab for processing.