Color-enhanced image of prostate cancer cells. Annie Cavanagh, Wellcome Images

In the past, cancer drugs have been indiscriminate killing machines—they would kill the cancerous cells, but take healthy cells too, sometimes making the patient even sicker. Precision medicine, or personalized medicine, is changing all that. Now oncologists can sequence the genome of the cancer cells and used drugs to target the specific mutations. All of this is advancing very quickly, but oncologists are wary about combining these specialized drugs. Each patient might need a different drug cocktail, but researchers need to understand how these drugs interact with one another and how they affect the patient as a result. Though drug companies have been doing tests on tumor samples outside the body, these experiments can’t account for how the cells interact with one another, changing how the treatment would work.

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Now researchers at MIT think they has found a way to test the efficacy and interactions of cancer drugs in the patient’s actual tumor, thanks to a gadget the size of a grain of rice. The device, according to a study published today in Science Translational Medicine, can hold tiny doses of up to 16 different drugs; once the device is implanted into the patient’s tumor (it is designed for tumors close to the surface of the skin), the doses seep out into the surrounding tumor. After about a day, the researchers remove the device and the parts of the tumor around it to see which drugs worked best to kill the cells. After a few on skin, prostate and breast cancer cells that were implanted in mice, the researchers tried the device on a particularly aggressive kind of breast cancer. The patients experienced very few side effects.

The researchers are planning to launch a clinical trial of their device next year. In the meantime, they are working on finding a more way to check the drugs’ efficacy while the device is still implanted,.