What is a circulating tumor cell chip?

Finding just one type of blood cell amidst all these cells can be like finding a needle in a haystack.  See more blood pictures.
Finding just one type of blood cell amidst all these cells can be like finding a needle in a haystack.  See more blood pictures.
Purestock/Getty Images

On the second season of the Discovery Channel's popular television program "MythBusters," Adam and Jamie tried to determine whether modern technology could make finding a needle in a haystack easy, thus rendering that old cliché outdated. The two men used fire, water, magnets and agitators to construct elaborate machines for finding the needles, but what they expected to take only an hour or so turned into an all-day event. Even with the best technology and ideas, it seemed that finding a needle in a haystack would still be a tough task.

When it comes to cancer, the needle in the haystack is the circulating tumor cell, or CTC. This blood cell breaks free from cancerous tumors and travels through the bloodstream to other parts of the body, a process known as metastasizing, or the spreading of cancer. Many cancer deaths are attributed to this blood-based distribution of cancerous cells. But despite the damage these cells do, they're very hard to find; for every 1 billion blood cells, there may be only one circulating tumor cell [source: Anthes].


Doctors have long known that these tiny cells could determine the effectiveness of a cancer treatment -- a decrease in CTC count would indicate that the cancer was responding to the therapy, while an increase or unchanged would reveal it was time to try something else. Yet, despite the impressive bounds that medical technology has made, doctors have lacked the proper means to count these cells. Previous devices used to track CTCs were only effective in about 20 to 60 percent of patients with advanced cancer [source: Anthes]. Since these devices were only able to locate the cells in advanced patients, it may have been too late to try another means of treatment. Additionally, the devices required pre-processing that sometimes destroyed the few available circulating tumor cells, making it difficult to search for other clues about the nature of the cancer.

But at the end of 2007 came some news that we might be on the way to finding these needles in our bloodstream, with a device far more simple and straightforward than anything Adam or Jamie could whip up. The invention of the circulating tumor cell chip holds the promise of giving doctors immediate feedback on how cancer treatments are working, even in the earliest stages, allowing them to try another method if necessary. Find out more about how this invention nabs those hard-to-find circulating tumor cells on the next page.


Finding Circulating Tumor Cells

­The CTC chip can find tiny cells within tiny blood samples.
­The CTC chip can find tiny cells within tiny blood samples.
Tom Grill/Iconica/Getty Images

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].

For more on cancer-related topics, see the links on the next page.


Lots More Information

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More Great Links

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  • Dolan, Kerry A. "Scanning for Cancer." Forbes. Aug. 15, 2005.
  • Gardner, Amanda. "Circulating Tumor Cells Reveal Insights into Lung Cancers." HealthDay Consumer News Service. July 2, 2008.
  • Geggel, Laura. "Microchip Detects Rare Circulating Cancer Cells." Focus Online. Jan. 11, 2008. (Nov. 24, 2008)http://focus.hms.harvard.edu/2008/011108/research_briefs.shtml#Toner
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