What is a circulating tumor cell chip?

So what is a circulating tumor cell chip, and how did the researchers at Massachusetts General Hospital develop it? The chip is about the size of a business card, though it handles much more information than a name and e-mail address. Because circulating tumor cells (CTCs) are so rare, the chip needs the ability to handle fairly large blood samples compared with the finger prick amount of blood that previous devices could handle. And within that large sample, the chip had to be able to pick out that elusive needle in the bloodstream, the CTC.

­The chip features 78,000 posts, each only the size of a human hair, for finding the cells. Each post is coated with antibodies that attract CTCs, but not other blood cells. Researchers attach the chip to a processor, and then blood samples pass very slowly over and through the chip; the speed of the blood flow was carefully designed so that all of the blood cells in a sample come in contact with a post. The whole process takes a few hours. As the blood comes in contact with the chip, the CTCs are pulled out of the sample by the antibodies. Then the chip can be examined with computer imaging or with a microscope to determine the cell count.

Researchers at Massachusetts General Hospital published their initial findings about the CTC chip in December 2007, with early testing indicating that the process works quite well. Using the chip, researchers collected CTCs in 115 blood samples from 68 patients with advanced lung, breast, prostate, colon and pancreatic cancer [source: MGH Cancer Center]. The study group included 116 blood samples, which means that CTCs were able to hide in only one blood sample; this sample was much smaller than the others [source: Smith]. And to prove that the chip wouldn't provide false results, 20 healthy blood samples were also examined. The chip, as would be expected, didn't detect any CTCs in those samples.

And it's not just advanced-stage patients who stand to benefit. The chip also found CTCs in 100 percent of the samples provided by patients in the early stages of prostate cancer [source: Smith]. For all patients, the chip holds great promise for tracking the effectiveness of certain cancer treatments. Researchers used the chip with nine patients undergoing cancer treatment, and they were able to measure declines in CTC counts that corresponded with decreases in the size of the tumor [source: MGH Cancer Center]. A decline in the cell count provides more immediate information about the effectiveness of medications or therapies, simply because the changes in the tumor take longer to show up [source: Anthes].

What's more, the chip captures these CTCs intact, which allows future research into the nature of these cells. In a follow-up study published in July 2008, researchers that by using the chip, they were able pull CTCs from 27 blood samples from patients with lung cancer [source: Gardner]. Researchers then used the cells to identify genetic mutations with a 92 percent success rate; this type of genetic mutation indicates whether a certain class of drug is an effective treatment [source: Massachusetts General Hospital]. With the chip, doctors can provide targeted therapy and avoid the secondary search for a needle in a haystack, that of finding the right therapy for a cancer that has more than one treatment.

Though these early successes are promising, larger clinical trials need to be conducted before we'll see the CTC chip in routine cancer examinations. However, the researchers don't believe that the chip should be expensive to produce, and a biotechnology company is already involved in commercial development of the project [source: Anthes].

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