May 19, 2009 A new implantable device that monitors a tumor for weeks, or months, could offer a simpler, less intrusive alternative to taking biopsies, which are traditionally used to diagnose the presence of cancer – and one that potentially offers a greater chance of successful treatment.

While biopsies are accurate, they only offer a snapshot of the tumor at a single moment in time. By the time you have test results, it may be too late to take action to prevent a secondary cancer, what's known as metastasis, developing. The ability of the new implant to monitor the tumor over a period of weeks or months offers doctors a lot more hope in being able to track its growth and observe how it responds to treatment. Such implants could one day provide up-to-the-minute information about what a tumor is doing – whether it is growing or shrinking, how it's responding to treatment and whether it has metastasized or is about to.

"What this does is basically take the lab and put it in the patient," says Michael Cima, professor of materials science and engineering at the Massachusetts Institute of Technology, who developed the device along with researchers from MIT. "This is one of the tools we're going to need if we're going to turn cancer from a death sentence to a manageable disease."

The cylindrical, five-millimeter implant contains magnetic nanoparticles coated with antibodies specific to the target molecules. Target molecules enter the implant through a semipermeable membrane, bind to the particles and cause them to clump together so they can be detected by magnetic resonance imaging (MRI).

The device is made of a polymer called polyethylene, which is commonly used in orthopedic implants, while the semipermeable membrane, which allows target molecules to enter but keeps the magnetic nanoparticles trapped inside, is made of polycarbonate, a compound used in many plastics.

Cima and his colleagues recently reported that their device successfully tracked a tumor marker in mice for one month. In the study, researchers transplanted human tumors into the mice, then used the implants to track levels of human chorionic gonadotropin, a hormone produced by human tumor cells.

The devices, which can be implanted at the time a biopsy is taken, can also be tailored to monitor chemotherapy agents, allowing doctors to determine whether cancer drugs are reaching the tumors. They can also be designed to measure pH (acidity) or oxygen levels, which reveal tumor metabolism and how it is responding to therapy. Cima believes an implant to test for pH levels can be commercially available in a few years, followed by devices to test for complex chemicals, such as hormones and drugs.

The implant not only can monitor existing treatments, but also the effectiveness of a range of new treatments that scientists are working on.

The implant is described in a paper published online in Biosensors & Bioelectronics in April.

Darren Quick

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