Distinguishing between benign and malignant melanocytic nevi by in vivo multiphoton microscopy

Authors:  M. Balu, K. M. Kelly, C. B. Zachary, R. M. Harris, T. B. Krasieva, K. König, A. J. Durkin and B. J. Tromberg

Journal:  Cancer Research 74: 2688-2697 (2014) 

Laser-scanning multiphoton microscopy (MPM) “sees” through the skin surface by generating 3D images with sub-micron resolution.  It provides real-time, label-free images of epidermal cells and elastin fibers via two photon excited fluorescence (TPEF) and collagen fibers via second harmonic generation (SHG).  The microscope used in this study is a novel clinical instrument, the “MPT-flex”, developed by JenLab, Inc., Germany.  This system is currently the only one of its kind in the U.S. 

The goal of the study was to evaluate the ability of MPM to distinguish among pigmented lesions in three groups:  common nevi, dysplastic nevi and melanoma.  Fifteen pigmented lesions were imaged in vivo (5 for each group) in 14 patients. After the lesions were imaged, biopsies were performed and standard histopathological slides were prepared. The MPM and histologic images were compared and 3 unique optical imaging biomarkers related to TPEF and SHG signals were used to quantify key histopathologic features. These imaging markers were combined to obtain a numerical “multi-photon melanoma index (MMI).”  The MMI scale ranged from 0-9, where 0 and 9 represent the lowest and highest probability of melanoma, respectively.  Indices corresponding to common nevi (0–1), atypical nevi (1-4) and melanoma (5-8) were significantly different (p<0.05), suggesting the potential of the method to distinguish between melanocytic nevi in vivo.  This study was performed according to an approved IRB protocol (Principal Investigator:  Dr. Kristen Kelly).

Malignant melanoma is the most deadly form of skin cancer and responsible for the vast majority of skin cancer-related deaths. The current approach for diagnosing melanoma is based on biopsy and histopathological examination, the same method used 100 years ago.  This procedure is invasive and the selection of a biopsy site is highly dependent upon the physician’s experience.  MPM is a new approach for bedside, non-invasive diagnosis of melanoma.  This was the first clinical translational study of MPM tomography in the U.S. for characterization and diagnosis of benign pigmented lesions and suspected melanoma.  A more comprehensive study with a larger number of patients is necessary in order to validate the proposed scoring algorithm and evaluate how well MPM technology can distinguish dysplastic nevi from common nevi and melanoma.  This could help dermatologists increase the accuracy of their diagnosis for pigmented lesions that fall into the borderline area and minimize the need for invasive biopsies.