Quantum sentinels.

Quantum physics may soon help physicians track whether a cancer has spread. In experiments in mice and pigs, a team of chemists and surgeons has used quantum dots--nanometer-scale crystals that emit light--to refine lymph node biopsies.

The first lymph node into which fluids from a tumor drain is called the sentinel node. If the cancer is spreading, it typically moves to this node before reaching other organs. In an increasingly popular diagnostic procedure for breast cancer and melanoma patients, surgeons remove sentinel nodes in search of cancer cells.

But sentinel nodes aren't always easy to spot during a biopsy. To find them, surgeons inject patients with a radioactive tracer that indicates the general region and a blue dye that stains the sentinel nodes. However, from outside a patient's body, surgeons can detect only the tracer, so they must probe surgically under skin and other tissues to find dyed nodes. The procedure can't be used for cancers deep inside the body, including lung and gastrointestinal cancers.

To try to circumvent that limitation, chemist Moungi Bawendi of the Massachusetts Institute of Technology and physician John Frangioni of Beth Israel Deaconess Medical Center in Boston have developed an imaging system using quantum dots that emit infrared light. Those wavelengths can penetrate several centimeters of tissue. When the dots were injected into pigs' lungs and gastrointestinal tracts, they traveled to the sentinel nodes associated with those organs, and glowed strongly enough to be sensed with an infrared detector through intact skin.

Bawendi reported the findings in Seattle on Feb. 13 at the annual meeting of the American Association for the Advancement of Science.--.E.K.