Re: Melanoma cancer/UV info

[Rick Mannix <rcmannix@uci.edu>]

At 04:15 PM 08/07/2000 -0500, you wrote:
>I received the following message from an astronomer I am acquainted with.  I
>am unaware of any reports of links between visible light and melanoma and/or
>genetic damage, but then I'm not a biologist or physician.  I'd appreciate
>any information anyone might have. 
------------------------------------------------

I did a quick search of the Medline data base. It sounds like visible
radiation can cause melanoma. There were several other studies that
implicated visible radiation in melanoma, as well.

======
Setlow, RB.  Spectral regions contributing to melanoma: a personal view.
Journal of Investigative Dermatology. Symposium Proceedings, 1999 Sep,
4(1):46-9. (UI:
20005399)
                      
 Language: English;  Pub type: JOURNAL ARTICLE; REVIEW; REVIEW, TUTORIAL

Abstract: Although human cutaneous melanoma is a complicated disease, the
principal etiologic
agent for its incidence in fair skin individuals is exposure to sunlight.
In order to understand the
epidemiology of melanoma - temporal effects, latitude effects, sunscreen
effects, albino
susceptibility, and differences from nonmelanoma skin cancer -one must
approach the problem
by obtaining clues indicating which wavelengths in sunlight are effective
in inducing melanomas.

One way is to use an animal model. At present, the only suitable model is a
backcross hybrid of
small tropical fish of the genus Xiphophorus, bred to have only one tumor
suppressor gene.
Single UV exposures to 7-d-old fish induce melanomas readily observable by
4 mo. The initial
slopes of dose-response curves for exposures at 302, 313, 365, 405, 436,
and 547 nm yield
sensitivity as a function of wavelength. This action spectrum does not look
like the spectrum for
light absorption by DNA (mostly in the UVB), but has appreciable
sensitivities in the UVA and
visible regions, and looks like a direct effect of light on DNA plus a
large indirect effect on DNA
by absorption of light by the intracellular melanin. Because the UVB is
only a fraction of solar
irradiance, one may calculate that 90% of melanoma induction in humans
arises from UVA and
visible, assuming the human spectrum is similar to the fish spectrum. 

The implications of this calculation are that (i) depletion of
stratospheric ozone will not affect melanoma incidence, (ii) an increase in
sun exposure time as a result of using UVB sunscreens could increase the
risk of melanoma, and (iii) the use of high UVA sun tanning devices could
increase the risk 


Rick Mannix
Health Physicist
Laser Safety Officer
University of California
Irvine, CA 92697-2725

949-824-6098
949-824-8539   fax
rcmannix@uci.edu
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