Formaldehyde-induced fluorescence in melanomas and other lesions. Diagnostic significance and mechanism of fluorescence.

We have investigated 40 cases of malignant melanoma (MM) and 81 other lesions including benign melanocytic neoplasms, other malignancies with a potential for confusion with MM, and tissues with biogenic amine-synthesizing apparatus for induction of formaldehyde-induced fluorescence (FIF). Unstained sections were examined with an ultraviolet light source for yellowish fluorescence. Twenty-four of 27 primary cutaneous MMs and 11 of 13 metastatic MMs were positive. Formaldehyde-induced fluorescence was quenched by prior sodium borohydride treatment, suggesting monoamine origin. None of the ten intradermal, five junctional, or three blue nevi showed FIF, but two of eight compound nevi and two of six spindle cell nevi were positive for FIF. One of six large-cell undifferentiated carcinomas was positive; none of six mesenchymal sarcomas were positive; one of seven histiocytic lymphomas showed weak, granular, cytoplasmic fluorescence. Two of five carcinoid tumors and one case of medullary carcinoma of thyroid showed FIF. We conclude that FIF is a simple, reproducible, technique for aiding in the diagnosis of amelanotic melanomas.