Mutations in sunlight-induced melanoma arise from cyclobutane pyrimidine dimers (CPDs),
DNA photoproducts that are typically created picoseconds after an ultraviolet (UV) photon is
absorbed at thymine or cytosine. We found that in melanocytes, CPDs are generated for> 3
hours after exposure to UVA, a major component of the radiation in sunlight and in tanning
beds. These “dark CPDs” constitute the majority of CPDs and include the cytosine-
containing CPDs that initiate UV-signature C→ T mutations. Dark CPDs arise when UV …

Cutaneous malignant melanoma (CMM) is one of the most rapidly increasing cancers in the
western world (Bowden, 2004). Frequency of its occurrence is closely associated with skin
color and depends on geographical zone (Leiter and Garbe, 2008). Multiple epidemiological
studies in humans (Whiteman et al., 2007) and experimental studies with mouse melanoma
models suggest that sunburn during childhood confers the highest risk of melanoma
development later in life (Noonan et al., 2001). Ultraviolet radiation (UVR) from sunlight that …