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Friday, 22 March, 2002, 00:45 GMT
Pollution 'adds to sun cancer risk'
PCBs are environmental pollutants
The study examined a combination of sunlight and pollutants
Tests on mice suggest exposure to both sunlight and environmental pollutants can lead to tumours developing on parts of the body hidden from direct light.

Researchers from the University of Illinois College of Veterinary Medicine say their findings suggest similar work should be done to look at how humans are affected by the combination.

Environmental campaigners say this is a new theory, so needs further work, but welcomed the study's examination of a combination of factors, rather than looking at one potential carcinogen in isolation.

Preliminary results from the study were presented to the annual meeting of the Society of Toxicology in Nashville, in Tennessee, USA.

Because PCB-contaminated soil and sun exposure are both extremely common, we must look at this issue in humans

Dr Michael Warhurst, Friends of the Earth
The particular type of skin cancer which was found to be more common in the mice was non-melanoma skin cancer - the most common cancer in the UK, but one for which treatment is usually very successful.

The Illinois team exposed 77 hairless mice to either UV light, soil from a landfill site contaminated with polychlorinated biphenyls (PCBs) and polychlorinated dibenzofurans (PCDFs), a PCB by-product, or both UV light and PCBs.

PCBs were widely used in electrical components and in lubricants, paints and varnishes until they were banned in the late 1970s, but they remain in the environment.

Slow-growing tumours

In the study, researchers exposed the mice for 77 days.

Some of the mice were also then exposed to UV radiation five days a week for 28 weeks.

In those that were exposed to both the PCBs and the sunlight combination, there was a rapid growth of non-melanoma tumours on the stomachs of the mice - parts of their bodies which had not been exposed to the UV.

The tumours were slow growing and did not turn into the more serious type of skin cancer, squamous cell carcinomas.

Mice exposed to the PCBs but not exposed to the light did not develop such tumours.

By day 281 of the study, scientists saw that mice exposed to sunlight but not the contaminated soil had developed twice the number of skin tumours in light-exposed areas than those exposed to both sunlight and PCBs.

The researchers believe the contaminated soil, caused chloracne (an acne-like eruption associated with dioxin exposure), which then served as a sunscreen, at least during early stages of exposure to UV light.

PCB-exposed mice also ate more and grew fatter, regardless of exposure to light.

Interpretation caution

Professor Rhian Cope, who led the study which was funded by the American Cancer Society said: "The statistical power of our experiments leads us to believe that our results likely underestimate the strength of our conclusions.

"Because PCB-contaminated soil and sun exposure are both extremely common, we must look at this issue in humans."

He added: "Our results were complex, but it was clear that tumour growth was dependant on whether or not an animal's skin was irradiated.

"The only time we saw tumours at any site was in the presence of UV irradiation.

"It was clear that UV light promotes the development of tumours at non-light-exposed sites that were probably initiated by exposure to PCBs and PCDFs."

Dr Michael Warhurst, chemicals campaigner for Friends of the Earth, told BBC News Online: "This is interesting, but because it is so new, we need to be careful about how we interpret it"

But he welcomed the fact the study had looked at PCBs and sunlight's combined effects.

Additional findings are set to be presented to a conference on PCBs in the Czech Republic in May.

See also:

06 Feb 02 | Health
Sunbeds 'raise' skin cancer risk
28 Dec 01 | Health
Skin cancer websites 'misleading'
17 Mar 00 | C-D
Skin cancers
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