Seeing the stretch. The optical stretcher spots cancer cells by testing for unusual elasticity.

Physicists Develop Super-Sensitive Cancer Test

A pair of physicists has developed a laser scanner that they claim can detect cancer cells with far greater sensitivity than current lab methods. Clinicians are eyeing the device with cautious optimism.

Clinicians often want to know if a tissue sample contains cancerous cells. Such diagnosis is tricky because there are few molecular markers that set cancer cells apart from normal cells, and the results are often subjective. One major difference is a breakdown of the cell's internal cytoskeleton after it becomes cancerous. As a result, cancer cells are more elastic and amorphous than their healthy neighbors. But because these qualities are difficult to spot under a microscope, clinicians have to rely on other signs, such as tumor growth or changes in gene expression. The lack of sensitivity of these tests means that cancers are often treated late in their development.

Hoping to arm clinicians with a cytoskeleton test for cancer cells, physicists Jochen Guck and Josef Käs at the University of Leipzig, Germany, have developed a device they call the optical stretcher. The device takes advantage of the fact that when a cell is struck by an unfocused beam from an infrared laser, the light's momentum stretches the membrane ever so slightly. If the cytoskeleton has been broken down, or "fluidized", as it is in cancer cells, then the cell stretches dramatically. The optical stretcher measures this elastic response of cells within droplets as they pass through a pair of laser beams.

Sharing the first results from their optical stretcher, Käs caused a stir yesterday at the Physics2005 conference in Warwick, U.K. Using mixtures of healthy and cancerous cells from culture, the device correctly diagnosed cancer with a sample of just 50 cells, making it about 10,000 times more sensitive than the standard method of tagging cells with molecular markers. More important, says Käs, the stretchiness of cancer cells should allow doctors to predict how aggressive a cancer will be. Once cancer cells reach a critical degree of stretchiness, they can slip out of tissues and spread throughout the body. The earlier such cells can be spotted, the better the chance of successful treatment.

"The idea is ingenious and novel," says Michael Trendelenburg, a cancer biologist at the German Cancer Research Center in Heidelberg, Germany, "but what they need now are real clinical partners to see if it can work." Molly Brewer, a cancer biologist and clinician at the M.D. Anderson Cancer Center in Houston, Texas, adds that "there's a huge difference between cancer cells in culture and in the patient, so this needs much wider testing."

Related sites
Käs's site
About the cytoskeleton and cancer