One of the tenets of cancer surgery is obtained clear margins around a tumor. In other words, removing enough tissue to make sure you “got it all.” Currently, surgeons rely on a combination of imaging and pathology examinations to determine if the margins of a tumor are clear. A clear margin means that the edge of the tumor can be seen and there is normal tissue beyond the tumor edge. Relying on these detection methods during an operation is time-consuming, costly, and often imprecise. Now, imagine that you could simply look at the tissue and know where the tumor boundaries are. Wouldn’t that be easier, faster, and more reliable? It certainly would be, and researchers Aaron Mohs, Michael Mancini, and Shuming Nie may have found a clever way to achieve this using lasers and injectable dyes to identify the boundaries of tumors.
A 21st Century Wood’s Lamp
The methodology is familiar to many surgeons. The dye injected into the body is known as indocyanine green. Indocyanine green (ICG) is a cyanine dye with low toxicity and side effects. When injected into the vascular system, it binds with plasma proteins and is confined to the vascular system. The dye is cleared by the liver and has a half-life of ~3 minutes. When the dye is exposed to a laser, it emits a fluorescence which can be captured via a camera system and displayed on a monitor. Thus, this dye gives you a way to visualize blood supply in tissues in both presence and intensity. In plastic surgery, I commonly use a system (the SPY imaging system by Lifecell) to identify the blood supply in skin and tissue flaps. This is beneficial when performing reconstruction to know whether the mastectomy skin is going to live or not. Essentially, wherever you see the fluorescence, you have blood supply. The more intense the fluorescence, the greater the blood supply.
So what’s this got to do with Tumors?
The idea of using this technology to identify tumors is a clever adaptation of this technology. Many tumors have a significant increase in vascularity due to angiogenesis and high metabolic rates within the tumor. By using the dye and its corresponding fluorescence, in theory one can identify the borders of the tumor based on this increase in vascularity seen by injecting ICG and using a camera system to detect the fluorescence. In the study by Mohs, Mancini, and Nie, they used a handheld laser with a three-camera capturing system to create a composite image of the tumor in both mice and dogs. They found that in both settings, the dye accumulated preferentially in the tumor tissue over the normal tissue.
The Future is LASERS!
The future of this technology is to improve localization of the dye to the cancerous tissue. Rather than using variations in blood flow and vascularity, a large leap forward would be to identify ways to have tumor cell receptors capture and concentrate the dye. Thus tumor cells could be identified with higher precision and tumor margins accurately delineated. Recently, Mohs was awarded a $1.37 million dollar research grant from the National Institute of Biomedical Imaging and Bioengineering to optimize the system and test in mice. This is a pretty exciting idea and a much better use for lasers than reducing wrinkles!