Fluorescent Tumors - Cutting on the Glowing Line

For decades cancer surgeons have had two tools with which to guide their scalpel: their hands and their eyes. Surgical tumor removal is the cornerstone of many cancer therapies, but in 20-50% of patients, microscopic scraps of cancerous tissue are accidentally left behind, and eventually, the tumors return. During surgery, it’s been virtually impossible to know if the entire tumor has been removed — until now.

Recent clinical research at the University of Pennsylvania is zeroing in on a technique that allows surgeons to more precisely define the boundary between cancerous and noncancerous tissue by making tumors fluoresce.

Before surgery, doctors inject a dye into the bloodstream, known as indocyanine green, or ICG, and wait about 24 hours for the dye to accumulate within the tumor. Because tumors grow so quickly, they stretch and develop “leaky walls,” allowing ICG to infiltrate and collect in the tumor. After the dye seeps into the tumors, doctors use a near infrared, or NIR, imaging system to image the cancerous tissue, which glows green on the surgeon’s computer screen. This fluorescence allows surgeons to remove tumors more accurately and helps limit the traces of post-surgery cancer.

The study, led by Dr. Sunil Singhal and David Holt, and surgical professor at UPENN, was published in PLOS ONE.

After researching the fluorescence methods in mice and dogs, five patients in a clinical trial were treated using ICG and the NIR imaging system. In all five cases, the tumors fluoresced onscreen, showing the efficacy of this technique in humans. In one of the four patients, the tumor seemed to be located clearly in one part of the lung; the rest of the lung looked and felt normal according to doctors and pre-surgical tumor scans. But under NIR light, parts of the lung still fluoresced.

“We initially thought there was a problem with our machine,” said Holt. “But it turns out, that patient had diffuse microscopic cancer.” Confirmed by biopsy, the patient received proper treatment and survived.

But there are still a few issues to work out. The ICG-NIR imaging technique was unable to distinguish between noncancerous inflamed tissue and cancerous tumors. If normal tissues are inflamed, chances are they also have leaky vessels, allowing dye to collect, just as it collects in tumors. In future research, Holt hopes that tumor-specific dyes can be used to differentiate and avoid confusion between noncancerous inflamed tissue and cancer.