Sunscreen not enough to protect against skin cancer
12th June 2014 – The latest research, published in the journal Nature indicates that sunscreen should be used in combination with other protection, such as clothing and staying in the shade.
It also explains more about how ultraviolet light, or radiation (UVR), contributes to the development of melanoma, a type of skin cancer.
According to Cancer Research UK, each year approximately 13,300 people living in the UK are diagnosed with melanoma. It is one of the most common types of cancer in people who are 15 to 34 years old, and people over 80 years old have the highest incidence of melanoma.
Behind the research
Scientists at Cancer Research UK's Manchester Institute at the University of Manchester and The Institute of Cancer Research in London examined the molecular effects of UVR on the skin of mice. It is known that UVR from the sun (as well as sunbeds) damages the DNA in skin cells, which can lead to melanoma, but how this happens at a molecular level has been unclear.
The scientists expressed mice with a faulty BRAF gene, which is known to increase the risks of developing melanoma. After a month, they shaved the backs of these mice and protected half of each back with an UVR-protected cloth while exposing the other half to a low dose of UVR, enough to mimic mild sunburn in humans.
Within a 24-hour period they noticed a change in Trp53 – a gene that helps suppress tumours – and observed sunburn cells in the UVR-exposed skin; within seven days the skin was rough to the touch and thickened. These and other UVR-induced changes continued and the exposed skin darkened. All the BRAF-induced mice exposed to UVR developed tumours, with 98% of the tumours developing within the UVR-exposed area.
The scientists observed mutations in Trp53 in about 40% of the tumours. They have identified mutant Trp53 genes as being linked to UVR-induced DNA damage in melanoma in BRAF-induced mice.
Professor Richard Marais, study author and Cancer Research UK scientist at the University of Manchester, says:
"UV light has long been known to cause melanoma skin cancer, but exactly how this happens has not been clear. These studies allow us to begin to understand how UV light causes melanoma.
"UV light targets the very genes protecting us from its own damaging effects, showing how dangerous this cancer-causing agent is."
UVR and sunscreen
The scientists also explored whether sunscreen protected healthy cells against melanoma when exposed to UVR. To do this they applied an SPF50 factor sunscreen to half the exposed shaven area on mice 30 minutes prior to exposure to UVR, with the other half of the shaven area covered by an UVR-protected cloth.
They found the immediate affects of UVR exposure the same on both the cloth-protected and sunscreen-protected skin, such as no darkening of the skin. However, all the sunscreen-protected UVR-exposed BRAF-induced mice developed tumours within 15 months (at a median latency of 7.5 months). While this is a significant reduction compared to unprotected mice, it is also a noticeable increase compared to mice that were not exposed to UVR. BRAF-induced mice protected by sunscreen developed fewer tumours on their backs than those unprotected, but still more than those not exposed to UVR. The scientists have concluded that although sunscreen did not provide complete protection it did delay UVR-driven melanoma in susceptible mice.