The animal is in what is called a “mouse hospital,” a new way of using mice to study cancer. Although mice have been studied in regular labs for years, the results often have been disappointing. Usually, the cancers were implanted under their skin, not in the organs where they originated. And drugs that seemed to work in mice often proved useless in humans.

The mouse hospital at Beth Israel Deaconess and a few similar ones elsewhere are at the forefront of a new approach to studying human cancers. The mice are given genes that make them develop tumors in the same organs as humans, which means the researchers need scanners to watch the tumors’ growth inside the animals’ bodies. So the mouse hospitals have tiny ultrasound machines, CT and PET scanners, and magnetic resonance imaging machines with little stretchers to slide the mice into the machines. They also have mouse pharmacies to formulate medicines in mouse-size doses and mouse clinical laboratories specially designed to do analyses on minute drops of mouse blood and vanishingly small quantities of mouse urine. That lets them follow cancers’ growth and responses to treatments.

“We’ve been obsessively focusing our attention on 2 percent of the genome,” said Dr. Pier Paolo Pandolfi, a professor of medicine and pathology at Harvard Medical School. This spring, at the annual meeting of the American Association for Cancer Research in Orlando, Fla., he described a new “biological dimension” in which signals coming from both regions of the genome participate in the delicate balance between normal cellular behavior and malignancy.