PHILADELPHIA - An experimental imaging tool that uses a targeted fluorescent dye successfully lit up the benign brain tumors of patients during removal surgery, allowing surgeons to identify tumor tissue, a new study from researchers at the Perelman School of Medicine at the University of Pennsylvania shows. The tumors, known as pituitary adenomas, are the third most common brain tumor, and very rarely turn cancerous, but can cause blindness, hormonal disorders, and in some cases, gigantism.

Findings from the pilot study of 15 patients, published this week in the Journal of Neurosurgery, build upon previous clinical studies showing intraoperative molecular imaging developed by researchers at Penn's Center for Precision Surgery can improve tumor surgeries. According to first author John Y.K. Lee, MD, MSCE, an associate professor of Neurosurgery in the Perelman School of Medicine at the University of Pennsylvania and co-director of the Center for Precision Surgery, this study describes the first targeted, near infrared dye to be employed in brain tumor surgery. Other dyes are limited either by their fluorescent range being in the busy visible spectrum or by lack of specificity.

"This study heralds a new era in personalized tumor surgery. Surgeons are now able to see molecular characteristics of patient's tumors; not just light absorption or reflectance," Lee said. "In real time in the operating room, we are seeing the unique cell surface properties of the tumor and not just color. This is the start of a revolution."
Non-specific dyes have been used to visualize and precisely cut out brain tumors during resection surgery, but this dye is believed to be the first targeted, near infrared dye to be used in neurosurgery. The fluorescent dye, known as OTL38, consists of two parts: vitamin B9 (a necessary ingredient for cell growth), and a near infrared glowing dye. As tumors try to grow and proliferate, they overexpress folate receptors. Pituitary tumors can overexpress folate receptors more than 20 times above the level of the normal pituitary gland in some cases. This dye binds to these receptors and thus allows us to identify tumors.

"Pituitary adenomas are rarely cancerous, but they can cause other serious problems for patients by pushing up against parts of their brain, which can lead to Cushing's disease, gigantism, blindness and death," Lee explained. "The study shows that this novel, targeted, near infrared fluorescent dye technique is a safe, and we believe this technique will improve surgery."

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