Sounding out cancer

Researchers at the University of Missouri-Columbia can now detect the spread of skin cancer cells through the blood by literally listening to their sound. The minimally invasive technique causes melanoma cells to emit noise, and could let oncologists spot early signs of metastases before they settle in other organs.

The team's method, called photoacoustic detection, uses a laser to make cells vibrate and then uses acoustic techniques to pick up the characteristic sound of melanoma cells.

Doctors take a patient's blood sample and separate the red blood cells and the plasma. The remaining white blood cells could also contain cancer cells in a melanoma patient. The doctors then put the sample in saline solution and expose it to rapid-fire sequences of brief but intense blue-laser pulses, each lasting five billionths of a second.

In lab tests, the team was able to detect melanoma cells obtained from actual patients, showing that the method can spot as few as ten cells in saline solution. The dark, microscopic granules of melanin contained in the cancer cells absorb the energy bursts from the blue laser light, going through rapid cycles of expanding as they heat up and shrinking as they cool down. These sudden changes generate relatively loud cracks which can be detected.