First published June 30, 2019.
File photo of a laser medical procedure, not the Cytophone device. (Capifrutta/iStock)
In 2019 a team at the University of Arkansas for Medical Sciences (UAMS) reported a device that shines laser light through the skin to find melanoma cells travelling in the blood, and that appeared to destroy some of those cells at the same time. Called the Cytophone, it was tested on people rather than only in the lab, which is what made headlines. It is not a cancer cure: it is an experimental detection tool with a promising side effect, and it so far works mainly for melanoma.
Here is what the researchers did, how the device works, what the numbers really mean, and why the work matters for the future of cancer monitoring.
What the researchers actually did
The study, led by Ekaterina Galanzha with senior investigator Vladimir Zharov and funded by the US National Cancer Institute (NCI), was published on 12 June 2019 in Science Translational Medicine. Participants placed a hand in a custom holder while the device scanned blood vessels just under the skin.
First, 18 people with melanoma and 10 without it helped set baselines and train the computer program that reads the signals. Then another 10 people with melanoma were tested to check that the method worked. Across the people with melanoma, the device detected circulating cancer cells in 27 of 28. No one reported pain or changes to their skin.
Why cancer cells in the blood matter
Most cancer deaths are caused not by the original tumour but by metastasis: the spread of cancer to other organs. To spread, cells break away from a tumour and travel through the blood or lymph. These are called circulating tumour cells, or CTCs.
CTCs are extremely rare. Even in people with metastatic disease there may be only one to ten in a millilitre of blood, a sample that also holds millions of white blood cells and around a billion red ones. Finding them is like looking for a few specific grains of sand on a beach. Today's tests, known as liquid biopsies, usually work on a blood sample drawn with a needle; the CellSearch system, for example, is cleared by the US Food and Drug Administration for counting CTCs in some cancers. A small sample can easily miss cells that are present elsewhere in the body's roughly five litres of blood.
A tool that could check much more blood, without needles, could in principle spot spreading cancer earlier, show whether treatment is working and track people at risk of relapse.
How the Cytophone works
The device uses a technique called photoacoustics: turning light into sound. Short laser pulses are aimed at a blood vessel under the skin of the hand. Melanoma cells usually contain melanin, the dark pigment that colours skin and moles. When a pigmented cancer cell passes through the beam, the melanin absorbs the light, heats up in an instant and produces a tiny pressure wave. An ultrasound sensor on the skin picks up that wave as a signal.
Ordinary blood cells absorb much less of the light in the way that melanin does, so the cancer cells stand out. According to the NCI, the system could pick up a single cancer cell in a litre of blood, about 1,000 times more sensitive than existing methods, with specificity estimated at 95%. Because blood keeps flowing past the sensor, the device can, over a period of hours, examine a person's entire blood volume. Media reports at the time described it scanning about a litre an hour.
Detecting and destroying: the "96%" claim explained
The surprise came during testing. The researchers noticed that the CTC signals in patients dropped over time while the device was running. The explanation is that the rapid heating can make vapour nanobubbles form around the melanin, which expand and collapse and tear the cell apart. Red blood cells also contain pigment but, the team reports, do not form these bubbles, so they appear to be spared.
Zharov told IEEE Spectrum that "in one patient, we destroyed 96 percent of the tumor cells," adding that the laser was not even at full power. That figure needs context. It describes the share of circulating cells measured in one participant's blood during the test, not the removal of all cancer from that person's body. In separate lab tests on patients' blood samples, one hour of laser exposure markedly reduced tumour cells, by as much as 11-fold in one case, but the effect varied from patient to patient and probably depends on how much pigment each cell carries.
Zharov's group had been working on laser-based cancer tools for years; in 2017 UAMS announced their nanobubble "spaser," billed as the world's smallest laser, designed to target cancer cells at the cellular level.
The limits: what this study did not show
Headlines in 2019 said scientists had "a laser that kills cancer in the blood." That framing goes further than the evidence. Several important limits apply:
- It is melanoma-specific for now. The method relies on the pigment in melanoma cells. Other cancers would need a different label, such as gold nanoparticles that attach to cancer cells; the team has tried that approach for breast cancer in mice and in patient samples.
- The study was small. It was a feasibility study with a few dozen participants, designed to test detection rather than treatment.
- The main tumour is untouched. Destroying some cells in circulation does not remove a primary tumour or metastases already growing in organs.
- No survival benefit has been shown. Nobody yet knows whether removing CTCs this way would slow the spread of cancer or help people live longer.
Kelly Nelson of the MD Anderson Cancer Center, who was not involved, told the NCI that much more research is needed before the device could be used widely.
Where the Cytophone fits among other devices
Zharov has described the Cytophone as the first device of its kind demonstrated in humans. Many other teams have tried to capture or count CTCs, and reviews of the field list dozens of approaches. One example is a wrist-worn device from University of Michigan researchers, designed to collect CTCs from blood over several hours. What made the Arkansas work stand out was the combination of no needles, a very large volume of blood examined, and the hint of a treatment effect.
The researchers' next steps were to build more devices for larger melanoma studies and to test whether the Cytophone could serve as an early screening and monitoring tool. In the 2019 study, all three participants with stage II melanoma had circulating cells detected, which suggests cancer cells may enter the blood earlier than many assumed.
What this means for patients today
The Cytophone is a research device, not a treatment you can request at a clinic. For now, the most effective protection against melanoma remains prevention and early detection: sun protection, avoiding sunbeds and checking your skin for new or changing moles. Anyone worried about a mole, or living with a melanoma diagnosis, should talk to a doctor about the tests and treatments that are available and proven today.
Even with its limits, the study is a good example of how cancer research moves: a tool built to see something rare turned out to affect it too, and that opens a new question for careful, larger trials to answer.
Sources: National Cancer Institute: Cytophone detects melanoma cells in blood; Galanzha et al., Science Translational Medicine (2019); ScienceAlert; Wikipedia: Circulating tumor cell.
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