Surgical Probe Distinguishes Between Tumor Margins and Healthy Tissue

A new surgical tool that uses light to ensure surgeons removed all of a cancerous tumor was found to correlate well with traditional pathologists' diagnoses, according to a clinical study showing that the tool could soon enable reliable, real-time surgical guidance.

The interdisciplinary research team was led by Stephen Boppart, MD, a medical doctor and a professor of electrical and computer engineering and of bioengineering at the University of Illinois. The team conducted the study using 35 patients with breast cancer at the Carle Foundation Hospital in Urbana, Illinois. The results appear in Cancer Research (2015; doi: 10.1158/0008-5472.CAN-15-0464).

One difficult but crucial determination for surgeons and tissue pathologists is figuring out where a tumor ends. A solid tumor may be easily identifiable, but the tissue around the main body of the tumor, known as the margin, may contain cancerous cells as well. Because of this, excess tissue surrounding the tumor is typically removed, but the question lingers of whether any cancer cells remain to re-emerge later as tumors.

"In almost all solid-tumor surgeries, there's a question of margins," said Boppart. "Typically, surgeons will remove the tissue mass that contains the tumor and will send it to the lab. The pathologist will process, section, and stain the tissue, then examine the thin sections on microscope slides. They look at the structure of the cells and other features of the tissue. The diagnosis is made based on subjective interpretation and often other pathologists are consulted. This is what we call the gold standard for diagnosis."

The new device is a hand-held probe based on optical coherence tomography (OCT), a technology that uses light to image tissue in real time. Cancer cells and normal tissue scatter light differently because they have different microstructural and molecular features, Boppart explained; so OCT gives physicians a way to quantitatively measure the cellular feature of a tumor. Surgeons can pass the OCT wand over a section of tissue and see a video on a screen, with no special chemical stains or lengthy tissue processing required.

"In many cases, you can't tell the difference between cancer cells and normal tissue with the naked eye, but with OCT they're very different," said Boppart.

In the clinical study, surgeons treated patients according to the standard surgical procedure, but OCT data were collected from the margins of the tumor cavity and the resected tissue mass during surgery so the results could be compared later.

The study found that the OCT device analysis identified the differences between normal and cancerous tissue with 92% sensitivity and 92% specificity. They also found that the way that OCT spotted cancer in the removed tissue was closely correlated with the results from the postoperative pathology reports, which often came days later.

"For the first time, this study demonstrates the use of OCT for imaging tumor margins within the tumor cavity, in the patient, during surgery," Boppart said. "It is likely better to check to see if any residual tumor cells might be left behind, rather than checking the tissue mass that was taken out. Then, the surgeon can intervene immediately."

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