Laser technique offers optical biopsy

Scientists have developed a new tool that could significantly improve the sensitivity of melanoma screening techniques.

Currently, the majority of melanoma diagnoses are made clinically by eye, but even visualisation by a skilled dermatologist can miss up to 15% of lesions. Moreover, studies have also found that pathologists can fail to agree on a diagnosis in 14% of biopsy samples. As a result, doctors tend to act cautiously and "when in doubt, cut it out", leading to a high false-positive rate and over-treatment of benign lesions.

Now clinicians could soon have a new weapon with which to combat the problem. Writing in Science Translational Medicine, Duke University researcher Thomas Matthews and his colleagues have found that a laser technique called "pump-probing" can be used to detect the quantities of different forms of melanin in a skin sample. Using 42 biopsy specimens, which included a mixture of benign and melanoma lesions, the team exposed the tissue to two brief bursts of laser light of two slightly different wavelengths (colours).

The first burst of light (the pump) sensitises one form of melanin - called eumelanin, which is darker and increases in concentration proportionally in malignant cells - to the second short laser blast (the probe) delivered shortly afterwards. This enabled the team to quantitate the relative concentrations of eumelanin and its lighter phaeomelanin relative in their samples. Comparing the levels of each enabled the researchers to correctly identify all of the genuinely-malignant specimens amongst the samples studied, although the team acknowledge that they have not tested their system against the subset of non-pigmented melanomas that don't make melanin.

However, for the majority of malignant melanomas, which are pigmented, the team point out that, apart from having the potential to dramatically improve current clinical protocols, at the laser powers they have been using, the system could readily be adapted to do diagnoses in-situ on a patient without needing to take a biopsy first.