Wavelengths effective in induction of malignant melanoma.

TLDR

Sunlight exposure is a recognized cause of malignant melanoma in fair‑skinned people, yet the specific wavelengths responsible remain unidentified, though DNA damage repair deficiencies dramatically increase risk. The study exposed 6‑day‑old Xiphophorus fish to narrow bands at 302, 313, 365, 405, and 436 nm, repeated exposures at each wavelength, and assessed melanoma development four months later to estimate wavelength‑dependent sensitivity. Melanoma induction was most sensitive to 365, 405, and possibly 436 nm, indicating that wavelengths absorbed by melanin—not directly by DNA—drive tumorigenesis, with 90–95 % of natural‑sunlight–induced melanomas attributable to wavelengths above 320 nm (UV‑A and visible).

Abstract

It is generally agreed that sunlight exposure is one of the etiologic agents in malignant melanoma of fair-skinned individuals. However, the wavelengths responsible for tumorigenesis are not known, although DNA is assumed to be the target because individuals defective in the repair of UV damage to DNA are several thousandfold more prone to the disease than the average population. Heavily pigmented backcross hybrids of the genus Xiphophorus (platyfish and swordtails) are very sensitive to melanoma induction by single exposures to UV. We irradiated groups of five 6-day-old fish with narrow wavelength bands at 302, 313, 365, 405, and 436 nm and scored the irradiated animals for melanomas 4 months later. We used several exposures at each wavelength to obtain estimates of the sensitivity for melanoma induction as a function of exposure and wavelength. The action spectrum (sensitivity per incident photon as a function of wavelength) for melanoma induction shows appreciable sensitivity at 365, 405, and probably 436 nm, suggesting that wavelengths not absorbed directly in DNA are effective in induction. We interpret the results as indicating that light energy absorbed in melanin is effective in inducing melanomas in this animal model and that, in natural sunlight, 90-95% of melanoma induction may be attributed to wavelengths > 320 nm--the UV-A and visible spectral regions.