Broadcast Monday 13 September 1999
with Rae Fry
Summary: A recent Australian study on the efficacy of sunscreens in protection against skin cancer has just been published.
‘Slip, Slop, Slap’ Rap
Rae Fry: You can probably remember more than one version of that classic ‘slip, slop, slap’ campaign. And many of us have dutifully followed the message it offers. But how much evidence is there that slopping on sunscreen actually prevents skin cancer? A Queensland study, thought to be the longest term trial of sunscreen ever, has just announced its results. And they may be a surprise to some. They showed sunscreen to be definitely effective against only one kind of skin cancer, and not the most deadly kind. So, have we been duped? Well the story is more complicated than that.
What their evidence tells us is that adults’ use of sunscreen probably doesn’t do much for the other kinds of cancer.
The head of the study is Professor Adele Green, from the Queensland Institute of Medical Research.
Adele Green: What we did was with a very dedicated and marvellous group of residents in the township of Nambour, which is just 100 kilometres north of Brisbane, for five years, we asked one half of them to apply sunscreen every day, SPF 15+ sunscreen, and we gave this to one random half of the 1600 people who were helping us, who’d been randomly selected from the electoral roll from Nambour, and the other 800 or so people were asked to continue using sunscreen in the usual way, which could have been not at all, or it could have been just occasionally when they went down to the beach. In fact that’s when most of the people we found do use sunscreen is for recreational purposes only.
There are two major forms of skin cancer that we wanted to look at in this trial. One arises at the more deep levels of the skin and that’s called basal-cell carcinoma. And that’s by far and away the most common type of cancer in white-skinned people actually. And the other was squamous-cell carcinoma, which is actually the more serious of the two. The squamous-cell carcinoma arises from higher up in the skin.
Rae Fry: Now there is a third kind of skin cancer isn’t there, melanoma?
Adele Green: Yes. Melanoma is, people don’t really realise I think, because it gets all the press, because of course it’s so dangerous. They’re quite rare really, and we counted, of course, the melanomas during the trial, but we only found 12 in the whole five-year period, and of course this is just simply not enough cancers of the melanoma type to be able to draw conclusions in a scientific manner.
Rae Fry: So what you were looking for then was, was there any benefit of putting on sunscreen every day in preventing against the carcinomas, these two most common kinds of skin cancer?
Adele Green: Yes, exactly.
Rae Fry: And what did you find?
Adele Green: Very pleasingly, we found that one type of cancer, the squamous-cell carcinoma, the numbers of tumours of this particular type, were significantly decreased, in fact decreased by 40% in the group who were applying the sunscreen on a daily basis.
Rae Fry: Were you surprised to find that amount of effect over what is for cancer actually, a fairly short period, five years?
Adele Green: Yes, that’s a very good point. Squamous-cell carcinoma takes years to develop. Most white-skinned Australians and fair-skinned Australians have got many pre-cancerous cells in their skin, what we call initiated cells, where the cancer process probably has already started, way back in childhood, adolescence, young adulthood, with all the exposure we get when we’re young. But it requires that last stoking, if you like, of the disease process by sunlight, right till the very end, to be able to express the disease clinically. If we can halt that process further along, then we can actually prevent the cancers from appearing, and this is really what we’ve done with the squamous-cell carcinoma.
Rae Fry: And were you surprised not to find an effect on basal-cell carcinoma?
Adele Green: I guess post hoc, we weren’t surprised. There are many studies now that are showing increasingly that basal-cell carcinoma really behaves quite differently. It probably starts much earlier in life, and we also know that basal-cell carcinoma takes a much smaller amount of ultraviolet radiation to form. Therefore you see basal-cell carcinoma on the back, and we get it earlier in life. You’ll see young adults of say late 20s, early 30s having basal-cell carcinoma. So you see everything has shifted back.
Rae Fry: I saw one newspaper report that said that your study said that sunscreen does not prevent basal-cell carcinoma.
Adele Green: That really is not giving the full story. We found that sunscreen, put on over a mere five years in an adult who might have lived 60 years, does not prevent basal-cell carcinoma. Now that’s quite a different statement, because as we’ve said this is a cancer that probably needed all its initiation earlier in life so it’s really to use a cliche that the horse has already bolted and we’re trying to shut the gate far too late afterwards. We should be looking at preventing these sorts of cancers much earlier on. So really it’s fruitless to say that sunscreen absolutely doesn’t prevent basal-cell carcinoma. Certainly there is no evidence from our study but it’s such a small window of time in an adult’s lifelong sun exposure history.
Rae Fry: Is there any other evidence that tells us something about what’s going on there? I mean we’ve been told in Australia for at least 20 years now, to ‘slip, slop, slap’ but people of the younger generation have been putting on sunscreen since they were kids. Are their rates of basal-cell carcinoma going down?
Adele Green: Yes, they are. A recent study which was done in a polling survey out of Melbourne, which covered the whole of Australia, very gratifyingly they’re now showing for the first time that BCC rates seem to be falling now in the very youngest age groups who get skin cancer. So this is, Rae, I think very encouraging, that we are starting to have an effect.
Rae Fry: And what about melanoma, can you give me a brief picture of what we know and don’t know about how that can be prevented, if at all?
Adele Green: Melanoma is of course much trickier, and probably shares a lot of the characteristics that I’ve mentioned for basal-cell carcinoma, in that we know from migration studies that people who arrive from a temperate climate very early in life, are at just as high risk of melanoma as Australians who, of course, are at the highest reported risk of melanoma in the whole world. Can we prevent melanoma by keeping out of the sun? Again I would say a resounding ‘Yes’, but we need to time that prevention, move it back into the early part of life if we’re really going to have an effect.
Rae Fry: Professor Adele Green from the Queensland Institute of Medical Research.
Reference: Adele Green et al, ‘Daily sunscreen application and betacarotene supplementation in prevention of basal-cell and squamous-cell carcinomas of the skin; a randomised controlled trial”. The Lancet Vol. 354, August 28, 1999, pp- 723-729.