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Defined: Avatar

Mice have become even more valuable stand-ins in cancer research.

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avatar [av-ə-tär] n: a term appropriated from virtual role-playing games (and the eponymous movie) to describe laboratory mice that replicate cancerous cells from specific patients to test potential treatments.

As doctors race against the clock to find a cancer drug or combination of drugs that works for a particular patient, mice are becoming valuable stand-ins, so much so that Manuel Hidalgo, head of the Gastrointestinal Cancer Clinical Research Unit at the Spanish National Cancer Research Centre in Madrid, co-opted the term “avatar” for them.

After doctors excise cancerous tissue from a patient, researchers graft it beneath the skin of a genetically engineered mouse whose immune deficiencies hasten the cancer’s spread. The resulting tumor growth becomes a closely functioning model of the patient’s cancer.

One mouse is rarely enough. To diversify the possibilities for treatments, doctors remove the tumor after it has had time to grow inside the first mouse, divide it and repeat the process with other mice. This doesn’t happen swiftly—creating enough avatars for testing can take two to eight months—and that raises the risk that patients won’t survive to see the results. In a 2011 study, Hidalgo and other researchers tested 63 drugs in 232 treatment combinations for avatars containing tumors from 14 patients with advanced cancers. One patient died before the testing was complete, and for two others, no effective treatments were found. For the remaining patients, however, 17 possible treatments were identified.

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