by Sharon Beder
Finding Cures for Melanomas
Melanoma is a problem in that it not only kills people but it also spreads quickly. Currently there is no effective treatment for melanoma although it can be cut out if it is caught early enough. Luckily, with the education programmes now at work in Australia, 80% of people seek medical attention early enough for melanomas to be cut out before they spread. But there are 20 % who do not and unfortunately if it has spread beyond the skin then it is incurable, or virtually incurable.
Even with people who do present early, says Ross Barnetson, these melanoma tumours can still spread extremely early and it is not always obvious. You just need one or two little cells getting into the liver or wherever, or even into the lymph nodes, and that is it. You can't give them a cocktail of drugs and get rid of it like you would with leukemia, for instance. The only option with melanoma is to cut out what you can see and hope for the best. In 80% of the people that does the trick. That's why we are so particularly interested in melanoma.
The fact that some skin cancers regress, that is go away, is of special interest to Barnetson. Normally a tumour simply gets bigger and bigger but in some cases of melanoma a patient will get a tumour and then it will suddenly disappear. The only reason this is known is because sometimes a secondary tumour will turn up in the lymph nodes or somewhere and the patient might say that they had a black mark, which would have been the first tumour, but that it disappeared. Other skin tumours do that as well and it is presumed to be due to the immune system.
Barnetson has been involved in a study of regressive melanomas. He is comparing them with non-regressing melanomas by looking at the differences in the cells in each type. The object of this research is to find ways of inducing this regression artificially. It is known that cells communicate with each other using things called cytokines, which are a kind of chemical messenger. Barnetson assumes there are cytokines involved in the regression of a melanoma which tell it to destroy itself. In the non-regressing melanomas there is less evidence of lymphocytes, which are white blood cells, actually attacking the tumour. In regressing melanomas, however, there is tremendous activity by the white blood cells which are trying to destroy the tumour.
You can quite often tell when a melanoma is regressing, says Barnetson. You sometimes see areas of white skin in it, for instance, and there may be evidence of scarring. But some tumours, although they are progressing, still show some areas of regression, so it is not a simple process. It's not a simple matter of black and white; this one is progressing, this one is regressing. Quite a lot tumours show a bit of both.
If regression can be induced artificially, which Barnetson thinks will be possible within the next few years, then that would be great. We could inject the patient with cytokines and their tumour would go away and hopefully any secondary tumour would also go away too, he says. One would hope cells are not depleted when the mouse is exposed to UV light. It is unlikely that the retinoids put up a barrier to ultraviolet light in the way that sunscreens do since they are taken orally.
The next step is to go on and see whether retinoids prevent skin tumours. It has yet to be proven that irradiated mice fed on retinoids have protection against developing skin cancers. Barnetson expects this line of research will eventually result in the possibility of humans taking a daily pill or having a vaccination to prevent them from getting skin cancer. Our research will give us answers to the immediate questions during the next year or two. It will be more like 5 to 10 years before injections would come in for the prevention of melanoma he says.