Does solar exposure, as indicated by the non-melanoma skin cancers, protect from solid cancers?

[Celebration]

http://www.ncbi.nlm.nih.gov/pubmed/17540555?ordinalpos=21&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum

Does solar exposure, as indicated by the non-melanoma skin cancers, protect from solid cancers: vitamin D as a possible explanation.

BACKGROUND: Skin cancers are known to be associated with sun exposure, whereas sunlight through the production of vitamin D may protect against some cancers. The aim of this study was to assess whether patients with skin cancer have an altered risk of developing other cancers. METHODS: The study cohort consisted of 416,134 cases of skin cancer and 3,776,501 cases of non-skin cancer as a first cancer extracted from 13 cancer registries. 10,886 melanoma and 35,620 non-melanoma skin cancer cases had second cancers. The observed numbers (O) of 46 types of second primary cancer after skin melanoma, basal cell carcinoma or non-basal cell carcinoma, and of skin cancers following non-skin cancers were compared to the expected numbers (E) derived from the age, sex and calendar period specific cancer incidence rates in each of the cancer registries (O/E=SIR, standardised incidence ratios). Rates from cancer registries classified to sunny countries (Australia, Singapore and Spain) and less sunny countries (Canada, Denmark, Finland, Iceland, Norway, Scotland, Slovenia and Sweden) were compared to each other. RESULTS: SIR of all second solid primary cancers (except skin and lip) after skin melanoma were significantly lower for the sunny countries (SIR(S)=1.03; 95% CI 0.99-1.08) than in the less sunny countries (SIR(L)=1.14; 95%CI 1.11-1.17). The difference was more obvious after non-melanoma skin cancers: after basal cell carcinoma SIR(S)/SIR(L)=0.65 (95%CI=0.58-0.72); after non-basal cell carcinoma SIR(S)/SIR(L)=0.58 (95%CI=0.50-0.67). In sunny countries, the risk of second primary cancer after non-melanoma skin cancers was lower for most of the cancers except for lip, mouth and non-Hodgkin lymphoma. CONCLUSIONS: Vitamin D production in the skin seems to decrease the risk of several solid cancers (especially stomach, colorectal, liver and gallbladder, pancreas, lung, female breast, prostate, bladder and kidney cancers). The apparently protective effect of sun exposure against second primary cancer is more pronounced after non-melanoma skin cancers than melanoma, which is consistent with earlier reports that non-melanoma skin cancers reflect cumulative sun exposure, whereas melanoma is more related to sunburn.

PMID: 17540555

[trotsky]

1. That Vitamin D appears to protect against cancers is not in dispute.

But this article does not claim that a "protective tan" is responsible. Not the same as what you were claiming on the other thread.

[Celebration]

2. what it claims

Is that people who have the least serious types of skin cancer have fewer solid tumors.

[LeftishBrit]

3. Very interesting...

but there is some rather mixed evidence: some studies suggest a somewhat increased risk of other cancers in people with non-melanoms skin cancer; others, like this one, suggest a reduced risk. It may depend on the nature of the sample: in particular people with severely depressed immune systems, e.g. those on immunosuppressants to prevent transplant rejection, are more liable both to skin cancer and to some other cancers, especially lymphoma; and people in this category may affect the results. The best evidence seems to be that non-melanoma skin cancer is associated with an increased risk of lymphoma, but with a reduced risk of colorectal cancer; though one still has to be tentative about that.

Anyway, as my mother and I have both had non-melanoma skin cancer, it would be nice to think we're less liable to other sorts!

[Celebration]

4. well the study I quoted doesn't say one way or another on NHL, but

Here is a study saying that UV exposure reduces the risk of NHL

http://www.ncbi.nlm.nih.gov/pubmed/17653830?ordinalpos=9&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum

I don't doubt that various studies may show different things, due to populations studied and the size of the study.