Near Infra-Red Navigation (NAVI) System for Mohs Tumor Mapping

The incidence of non-melanoma skin cancers, i.e. basal cell and squamous cell carcinoma (BCC and SCC), in the US is over 5.4 million. Of these, BCC represents the majority, with an incidence of over 4 million. Recent guidelines published on the treatment of BCC and SCC establish Mohs micrographic surgery (MMS) as the treatment of choice for high-risk SCCs and BCCs and for those in cosmetically sensitive locations.

MMS involves the step-wise removal and subsequent histological examination of thin layers of cancer containing skin until only cancer-free tissue remains. At the initial layer, only clinically involved skin is excised. The excised tumor is oriented using purposeful marks on the tissue and color-coding. Using this orientation, a "Mohs map" is drawn to indicate where malignancy is seen histologically. For each following layer, orientation is maintained, and only margins with remaining malignant tissue are removed as indicated on the map. As the goal is to spare as much normal tissue as possible, Mohs layers are only a few millimeters thin. The average number of layers needed to remove an entire tumor per Mohs case is cited as 1.74. However, outlier providers - that take a fewer or higher number of layers to clear a cancer- do exist. While this could represent providers who see more complicated cases, and skin tumors are often more extensive than initially clinically apparent, the need to balance efficiency with the width of a layer likely also plays a role.

Fluorescence image guided surgery using Indocyanine green (ICG), an FDA approved near-infrared (NIR) dye, has been used for effective visualization of intra-osseous tumoral tissues in real-time, allowing surgeons to make intraoperative decisions for further resection of otherwise clinically-uninvolved tissue. The use of intradermal ICG in a cutaneous tumor during MMS could allow surgeons to directly visualize, and roughly map the extent of a primary skin cancer preoperatively and plan the Mohs procedure (i.e. the initial excision size and subsequent layer widths) accordingly. No current such mapping system exists for use in cutaneous tumors.

Thus, while MMS represents an effective methodology to remove malignant tissue and spare as much normal skin as possible, it is a lengthy process totaling several hours, and given the need for histological processing at each stage, its duration primarily correlates with the number of layers or stages needed. A pre-operative map of the extent of the tumor could allow for: (1) a larger first layer - on the initial excision, only clinically evident tumor is excised, but skin tumors are at times more extensive that clinically apparent; and the Mohs surgeon to take thicker subsequent layers as needed. Effective and accurate pre-operative tumor mapping with ICG therefore has the potential to reduce the total number of Mohs layers taken for a patient. This is effect would improve patient safety and quality of care, and reduce unnecessary financial burden associated with outliers. As a decreased number of layers would directly shorten the total procedure length, preoperative mapping also has the potential to help increase patient access to MMS.