Drawing blood no longer necessary

A technology for cancer detection that eliminates the need for drawing blood has been developed by researchers at Purdue University, West Lafayette, Ind. In addition to being less invasive, the new detection method is able to evaluate a much larger volume of blood than what can be drawn from a patient for analysis, notes Philip Low, professor of chemistry.

"In the initial stages of cancer, there are very few circulating tumor cells--cells that indicate the spread of cancer and initiate secondary tumor formation," Low explains. "By increasing the volume of blood analyzed, we improve the sensitivity of the test and allow for earlier diagnosis. If there are two cancer cells in every 50 milliliters of blood, odds are the cells would not be found in a 10-milliliter blood sample. However, the cells would be found in the 100 milliliters of blood that flow through large veins each minute."

Optical imaging provides high resolution and chemical specificity for cancer detection, but it usually suffers from limited penetration depth, making it hard to reach tumors inside the body, points out Ji-Xin Cheng, assistant professor of chemistry and biomedical engineering. "In vivo detection of circulating tumor cells in surface veins provides an excellent way to overcome this problem," Cheng reports.

"Circulating tumor cells provide a benchmark for disease progression and precise monitoring of their levels could lead to personalized treatment," Low declares. "This technique allows us to quantify the amount of circulating tumor cells present, as opposed to tests that provide a 'positive' or 'negative' result. Through this type of precise monitoring, a physician could evaluate the response to chemotherapy and adjust the dosage regularly so that only the exact amount needed would be administered. This could reduce the time a patient is treated and the serious side effects that occur."

The technique could provide doctors and patients results in a matter of minutes and save the medical industry millions of dollars in testing equipment. By directly labeling tumor cells while they are in the bloodstream, some of the costs and problems associated with testing drawn blood samples can be avoided.

"One sample can require five to 10 test tubes during the course of sampling, processing, and analysis--such as handling, labeling, and washing," states Cheng. "In addition, large hospitals can have more than 300 cancer patients in one day. Such a large influx can cause delays in sample processing and delays can affect the result of analysis."

The technique uses a fluorescent tumor-specific probe that labels tumor cells in circulation. When hit by a laser, which scans across the diameter of the blood vessel 1,000 times per second, the tumor cells glow and become visible. The researchers compared several methods and found two-photon fluorescence provides the best signal-to-background ratio. The technology is able to scan every cell that is pumped through the vessel.

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