Identification of melanoma cells by formaldehyde-induced fluorescence

We have employed the formaldehyde-induced fluorescence technique to establish the identity of cells derived from malignant melanoma and grown in tissue culture. Following exposure to formaldehyde vapor, melanoma cells exhibited specific, localized, green-yellow fluorescence which diminished in intensity with prolonged exposure to ultraviolet light. Melanoma cells which had not been exposed to formaldehyde vapor, and non-melanoma control cell lines which had been exposed to the vapor showed a faint green autofluorescence which was stable following prolonged exposure to UV light. Maintenance of melanoma cells in medium supplemented with tyrosine increased the intensity and number of cells demonstrating fluorescence. Both melanoma and non-melanoma cells grown in medium containing dopamine showed brilliant fluorescence with no apparent specificity. Although melanoma cells grown in cysteine showed decreased fluorescence, this may have been related to their impaired growth in medium containing this compound. The formaldehyde-induced fluorescence technique appears to be a simple accurate means for confirming the identity of cells which are derived from malignant melanoma and propagated in tissue culture.