CONTENTS

Introduction
Human Skin Cancer
Sunscreen and Fabric
The Mouse Model of Cancer
Studies Using Skin Tissue
Drugs and Sunlight
Plant and Algae Growth
Conclusion
Glossary
Bibliography

Genetic Factors

The second area of research being conducted by the Melanoma Unit is into the genetic make-up of people who get melanomas. Some people have more tendency to get moles than others quite apart from where they live and this tendency may be inherited. Factors such as a person's skin colour, how their skin reacts to sunlight, their hair colour, eye colour, all indicate whether they are more likely to get melanomas. However, the best indicator of the likelihood of getting melanomas is the number of moles a person has.

There is no question that people who have light or reddish coloured hair, who freckle easily and who burn without tanning are more likely to get moles. This skin characteristic is essentially inherited. A lack of an appropriate repair mechanism is thought to be the cause. When people with certain types of skin get burned, the skin cells are damaged and do not repair properly.

A genetics group in the Melanoma Unit is studying some aspects of this repair problem. The group is looking at melanoma which occurs within certain families because the genetic responses in these families seem to be worse than simply an inability to repair damage. Sometimes a grandparent as well as one or two members of the immediate family will have had melanomas. These families comprise about 5% of persons with melanoma and are said to have "familial melanoma". In these cases at least one other of the close relatives of a patient, i.e. parents or brothers or sisters, also have a melanoma. In the whole population there is statistically less than one chance in 50 of this happening if you assume no inherited genetic factors are involved, yet there are quite a lot of these families which have more than one melanoma in the family.

The tendency to get familial melanoma is to some extent independent of how many moles they have and more dependent on a person inheriting a genetic defect. A lot of work has already been done to try to localise, in this group of patients, exactly where the gene defect is actually located. If researchers can find out where the defect is there is even the possibility that the gene could be repaired using genetic engineering techniques to remove and replace the defective genes. In some of the rarer tumours this has actually been done but it is hasn't been done yet with common tumours. It is much more difficult in common diseases like melanoma to identify exactly where the gene is, but geneticists are hot on the trail in the case of familial melanoma.

As well as studying familial melanomas, the Melanoma Unit is looking at people with what is called the dysplastic naevus syndrome. These people also have an hereditary defect in their skin and produce a lot of unusual looking moles called dysplastic moles. These tend to run in families too and these people also have a higher incidence of melanoma. So there is more than one trail to follow in the search for the location of the genetic defect. It is more likely to be found by looking in both of those groups. Once it is found it will be possible to discover if the same genetic defect is actually caused by sunlight in those who have neither the dysplastic naevus syndrome nor familial melanoma. In other words sunlight itself rather than a basic gene defect may damage the gene specifically. "If that were found to be the case then medical science would be in a strong position to do something about it" says McCarthy.

In the course of a genetic study it is now possible to look at the genetic make-up of a cell using what are called "probes", which are sequences of amino acids resembling a gene. These can be matched to the sequence of amino acids in a person's chromosomes and show if there is an abnormality in a certain area of the chromosome or if there is an unexpected gene sequence. "American geneticists are currently carrying out a monumental effort to map the entire human gene sequence which they expect will take them ar least 30 years. If they can map it completely then it should be possible to say fairly easily whether something is abnormal or not and predict the onset of diseases and perhaps do something to prevent it," says McCarthy.