When removing a malignant tumor, a surgeon can’t see a single cancer cell left behind with the naked eye — or even 10,000 cancer cells. That’s a microscopic amount, which is why excised tumors currently get sent to pathologists. They can look at a few small sections of an excised tumor under the microscope and get an idea of whether the cancer was removed in its entirety. But what if a way were developed that allowed cancer surgeons to see right in the operating room, before the patient was closed back up, whether any cancer cells remained?
Your Dog editor-in-chief John Berg, DVM, is involved in cutting-edge research that will allow surgeons to do just that. In an investigation he conducted with fellow scientists at Duke University and MIT, he injected cancer-ridden dogs with a probe prior to their surgeries. The probe is a protein with one or more fluorescent molecules attached to it — it’s delivered intravenously anywhere from several hours to a day or two before the operation.
Once the probe is inside the body, cancer cells, to a much greater degree than normal cells, release enzymes that split the fluorescent molecules from the protein to which they’re attached. That activates them, so when a fluorescent light is shined on the tumor bed, where the surgeon may have left stray cancer cells behind, those molecules fluoresce at a particularly high level, and a special imaging device displays them on a computer monitor. The surgeon, in turn, can see what he missed, potentially even down to a single cancer cell, and remove it.
To date, a number of different protein-fluorescent probes have been investigated by researchers at different institutions, along with a number of imaging devices. “While it is really exciting, it’s not quite ready for prime time,” says Dr. Berg. “The imaging devices need some refinement to make them easier to use in the operating room. And we also need to understand better the specificity and sensitivity of the technology for detecting cancer cells not visible to the naked eye.”
But in the next five to 10 years, as the technology is perfected, whether the margins are clean or incomplete — as determined by examination of the tumor under a microscope after the surgery — will become less relevant. The cancer surgeon will have better assurance that he “got it all” before the dog even wakes up from the anesthesia.
