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British Medical Journal: Is sun exposure a major cause of melanoma? No

Prof Sam Shuster1. Professor Sam Shuster, honorary consultant
Author Affiliations
1. 1Department of Dermatology, Norfolk and Norwich University Hospital, Norwich NR4 7UY
1.

Every summer we are reminded about the dangers of the sun. Scott Menzies(doi: 10.1136/bmj.a763) argues that the risks of malignant melanoma are real, but Sam Shuster is unconvinced

The list of harmful things grows daily, freshly mined by descriptive epidemiology, a substitute for research that confuses association with cause. Although most disappear under the weight of their own inconsequence, the alleged increase in melanoma from ultraviolet radiation has survived on the life support of regular promotion. I am therefore setting out what is known, which is rather different from what is believed.

Does ultraviolet light cause melanoma?

There is solid descriptive, quantitative, and mechanistic proof that ultraviolet rays cause the main skin cancers (basal and squamous). They develop in pale, sun exposed skin,1 are related to degree of exposure and latitude,2 are fewer with avoidance and protection,3 4 are readily produced experimentally,4 and are the overwhelmingly predominant tumour in xeroderma pigmentosum, where DNA repair of ultraviolet light damage is impaired.
None of these is found with melanoma. Variation is more ethnic5 6 7 than pigmentary,8 and 75% occur on relatively unexposed sites,9 especially the feet of dark skinned Africans.6 7 The relation to latitude is small and inconsistent in, for example, Europe10 and the United States11; incidence and mortality fall with greater exposure7 8 9 10 11 12 13 14 15 16 17; incidence is unaffected or increased by use of sunscreens18 ; and the effect of sun bed exposure is small and inconsistent.19 In addition, melanomas are difficult to produce experimentally with ultraviolet 20 light and are far less common than non-melanoma cancers in xeroderma pigmentosum.
Therefore, the effect of ultraviolet light can only be minimal, and the case against a major role is clear. Attempts to relate light exposure to surface area and site are irrelevant, since the cell of origin of melanoma and its distribution are unknown. The suggestion that the poor correlation of melanoma to ultraviolet light is because the causal event is sunburn from intermittent exposure in early life13 14 15 16 17 21 is easily excluded, because the melanomas would then occur at the burn sites; there is no evidence for this, and it is unlikely that any will be found, because sunburn occurs in sun exposed sites, and these are not the sites at which melanomas occur.7 8
There is an association between melanoma and number of naevi,13 22 and naevi increase after exposure to ultraviolet light22 23; but this does not implicate ultraviolet light in the aetiology of melanoma, for the same reasons related to site. The likely explanation of the association is that stimulation of naevus growth by ultraviolet light simply increases the number of visible (and therefore countable) lesions. The associated histological changes can be indistinguishable from melanoma, as is the case with the benign lesions of lentigo maligna in elderly people, sun bed users, and psoriasis patients treated with psoralen and ultraviolet A; benign naevi stimulated by shave excision; and juvenile melanoma. Thus, unlike for squamous and basal cell cancers, there is no proof that ultraviolet light exposure is a significant cause of melanoma.

Is the reported increase in melanoma real?

In the past, naevi were left untreated and usually caused no harm. Then, fear of litigation and the search for early lesions led to removal of benign lesions; this introduced an ambiguity into histological classification, which eventually changed the definition of malignancy. Those who observed the process believe misdiagnosis of benign naevi explains the melanoma epidemic.24 This view is supported by the findings of the Eastern region of England that the increase in new "melanomas" during 1991-2004 was entirely due to benign naevi (Levell et al, personal communication); a melanoma mountain in Australia has also been attributed to confusion with a benign disease.25 The relation between incidence of new melanomas and higher social class26 is best explained by removal of benign naevi after health warnings and encouragement to attend "pigmented lesion clinics"-the middle classes are always first on the scene.27
The subjective histopathological criteria used to diagnose melanoma have become too vague for use and are commonly found in benign disease. This problem can be resolved only by research, including a blind re-examination of histological slides used for past and present diagnoses, and a better distinction between benign and malignant changes in naevi.24 27 Meanwhile, it can only be concluded that the reported increase in melanoma is probably an erroneous reclassification of benign naevi. Thus the question of whether ultraviolet light causes melanoma becomes irrelevant, because there is no case to answer.

Balancing the effects of ultraviolet light

Of course we know that ultraviolet light causes the common, virtually benign, and mostly trivial skin cancers and that, like smoking, it makes the skin look as if it has been well lived in. But is this enough to justify blanketing the sun when balanced against the possible advantages? We know the sun makes us feel better, although not how28; we need skin synthesis of vitamin D for our bones; ultraviolet light may protect against some forms of cancer29 including melanoma14; and it has important, unexplained immunological effects.30 We need to know much more before we can balance the biological books on ultraviolet radiation, even if we can now close the chapter on melanoma.24

Footnotes
• Competing interests: None declared.
References
1. ↵

Urbach F. Ultraviolet radiation and skin cancer. In: Smith KC, ed. Topics in photomedicine. New York: Plenum, 1984:67-104.
2. ↵

Gordon D, Silverstone H. Worldwide epidemiology of pre-malignant and malignant cutaneous lesions. In: Andrade R, ed. Cancer of the skin. Philadelphia: Saunders, 1976:405-55.
3. ↵

David H. Efficacy of sunscreens in protection against skin cancer.Lancet1999;354:699-700.

4. ↵

Honnavara S, Ananthaswamy N, Ullrich SE, Misiodo RE, Fourtanier A, Loughlin SM, et al. Inhibition of solar simulator-induced p53 mutations and protection against skin cancer development in mice by sunscreen. J Invest Derm1999;112:763-8.

5. ↵

Cress RD, Holly A. Incidence of cutaneous melanoma among non-Hispanic whites, Hispanics, Asians, and blacks: an analysis of California cancer registry data, 1988-93. Cancer Causes Control1997;8:246-52.
6. ↵

Rolón PA , Kramárová E, Rolón HI, Khlat M, Parkin DM. Plantar melanoma: a case-control study in Paraguay. Cancer Causes Control1997;8:850-6.

7. ↵

Garsaud P, Boisseau-Garsaud AM, Ossondo M, Azaloux H, Escanmant P, Le Mab G, et al. Epidemiology of cutaneous melanoma in the French West Indies (Martinique). Am J Epidemiol 1998;147:66-8.
8. ↵

Le Marchand l, Saltzman S, Hankin JH, Wilkens LR, Franke SJM, Kolonel N. Sun exposure, diet and melanoma in Hawaii caucasians. Am J Epidemiol2006;164:232-45.

9. ↵

Armstong K, Kricker A. The epidemiology of UV induced skin cancer. J Photochem Biol 2001;63:8-18.

10. ↵

Crombie IK. Distribution of malignant melanoma on the body surface.Br J Cancer1981;43:842-9.

11. ↵

Crombie IK. Variation of melanoma incidence with latitude in North America and Europe. Br J Cancer1979;40:774-81.

12. ↵

Weinstock MA, Colditz,BA, Willett WC, Stampfer MJ. Bronstein, BR, Speizer FE. Nonfamilial cutaneous melanoma incidence in women associated with sun exposure before 20 years of age. Pediatrics1989;84:199-204.

13. ↵

Tucker MA, Goldstein AM. Melanoma etiology: where are we?Oncogene2003;22:3042-52.
14. ↵

Berwick M, Armstrong BK, Ben-Porat L, Fine J, Kricker A, Eberle C, et al. Sun exposure and mortality from melanoma. J Nat Cancer Inst2005;97:95-199.
15. ↵

Veierød MB, Weiderpass E, Thörn M, Hansson J, Lund E, Armstrong B, et al. A prospective study of pigmentation, sun exposure, and risk of cutaneous malignant melanoma in women. J Natl Cancer Inst2003;95:1530-8.
16. ↵

Oliveria SA, Saraiya M, Geller AC, Heneghan MK, Jorgensen C. Sun exposure and risk of melanoma. Arch Dis Child2006;91:131-8.
17. ↵

Elwood JM, Gallagher RP, Hill GB, Pearson JCG. Cutaneous melanoma in relation to intermittent and constant sun exposure-the western Canada melanoma study. Int J Cancer2006;35:427-33.
[CrossRef]
18. ↵

Dennis LK Beane LE, Freeman PD, VanBeek MJ. Sunscreen use and the risk for melanoma: a quantitative review. Ann Int Med2003;139:966-78.

19. ↵

Gallagher RP, Spinelli JJ, Lee TK. Tanning beds, sunlamps, and risk of cutaneous malignant melanoma cancer. Epidemiol Biomarkers Prev2005;14:562-6.

[CrossRef]
20. ↵

Setlow RB, Woodhead AD, Grist E. Animal model for ultraviolet radiation induced melanoma: platyfish-swordtail hybrid. Proc Natl Acad Sci1989;86:8922-9026.

21. ↵

Khlat M, Vail A, Parkin M, Green A. Mortality from melanoma in migrants to Australia: variation by age at arrival and duration of stay. Am J Epidemiol 1992;135:1103-13.
22. ↵

Van Schanke A, van Venrooij G, Jongsma M, Banus HA, Mullenders LHF, van Kranen HJ, et al. Induction of nevi and skin tumors in Ink4a/Arf Xpa knockout mice by neonatal, intermittent, or chronic UVB exposures.Cancer Res2006;66:2608-15.

23. ↵

Harrison SL, MacLennan R, Speare R, Wronski I. Sun exposure and melanocytic naevi in young Australian children Lancet1994;344:1529-32.
[CrossRef][Medline][Web of Science]
24. ↵

Shuster S. Sun and the skin; a violation of truth. In: Feldman S, Marks V eds. Panic nation. London: John Blake, 2006:259-82.
25. ↵

Armstrong BK, Kricker A. Cutaneous melanoma. Cancer Surveys1994;19-20:219-40.
26. ↵

MacKie RM, Hole DJ. Incidence and thickness of primary tumours and survival of patients with cutaneous malignant melanoma in relationship to socioeconomic status. BMJ 1996;312:1125-8.

27. ↵

Shuster S. Diagnoses of melanoma need further investigation.BMJ1996;313:627/b-8.

28. ↵

Nissen JB, Avrach WW, Hansen ES, Stengaard-Petersen K, Kragballe K. Increased levels of enkephalin following natural sunlight (combined with salt water bathing at the Dead Sea) and ultraviolet A irradiation. Br J Derm 1998;139:1012-9.

[CrossRef][Medline][Web of Science]
29. ↵

Porojnicu A, Robsahm TE, Dahlback A. Seasonal and geographical variations in lung cancer prognosis in Norway. Does vitamin D from the sun play a role? Lung Cancer2007;55:263-70.

[CrossRef][Medline][Web of Science]
30. ↵

Kripke ML. Ultraviolet radiation and immunology: something new under the sun. Cancer Res1994;54:6102-5.
BMJ 2008; 337:a764 doi: 10.1136/bmj.a764 (Published 22 July 2008)
Cite this as: BMJ 2008; 337:a764

 

 

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