Melanoma and UV

Circumstantial evidence for the linkage ...

The other day, I was asked (by George again) to help him fact-check a claim on Facebook (not that I frequent such places) saying "The sun doesn’t cause cancer unless you bake chemicals on your skin", as well as claiming that “the chemicals in sunscreen cause skin damage”. Apparently it was posted by a minor Australian celebrity. Not a very bright one, I venture to suggest.

Here’s my response to George …

There’s a wealth of epidemiological evidence for UV exposure being the cause of skin cancer, but there are also some skin cancers that may not be related to UV exposure, suggesting a strong genetic predisposition may be at play. We know that Celtic colourings are most at risk (pale skin, red hair, blue eyes). For some skin cancer types (e.g., melanoma), the risk seems to be related to the number of sunburn episodes, particularly in childhood, rather than cumulative exposure. Its effects also seem to be systemic in some cases, such as when melanomas appear in body-areas not normally exposed to sunlight.

However, the gold standard evidence - from a Randomised Control Trial (RCT) - is missing for humans because it would be impossible to get ethical approval to carry out experiments where you’re deliberately trying to induce skin cancer in the unlucky arm of the experiment. However, you can find many RCTs in the literature that use hairless mice instead of humans. These show a clear correspondence between UV exposure and development of skin tumors (even for mice that don’t use facial creams 😊).

But you should really check this with a skin specialist rather than an atmospheric scientist.

I suggested a couple, and apologise if it made work for any of you. But if it did, I hope they can add comments to this post, as I too would be interested in their views.

In the meantime, I found some statistics of melanoma incidence from the web site for Australia’s Institute for Health and Welfare that my colleague Robyn Lucas put me on to. Here's a clip from it …

The plots show that incidence rates for ‘melanoma of the skin’ are about 30 percent greater in Queensland than for Australia as a whole. They’re also much higher for men. Both these suggest that UV exposure is a risk factor. UV levels are higher in Queensland than for Australia as a whole. And, my perception is that men spend more time outdoors exposed to it than women. Or perhaps they’re not as careful about sun-avoidance. The lower rates in the Northern Territory probably reflect differences in ethnic mix, with a higher proportion of Aborigines. Their skin-type is much better adapted to the extreme UV levels at those latitudes.

Rates have doubled since the 1980s, though have levelled off in recent years. I wondered whether the early increases reflected a diagnosis problem rather than a true increase in incidence rates. I asked Robyn, who replied “my guess is the increase over time is better diagnosis - particularly of thin lesions in old people. I haven't plotted these data by age group, but my understanding is that incidence is decreasing in younger age groups despite overall increasing incidence”.

If it is indeed decreasing in younger age groups, that’s a huge success for Australia’s UV safety awareness campaigns. Well done!

Rates of ‘invasive melanoma’ are lower. Back in 2019 it was reported that ‘the most recently available data show that in 2014/2015 about 50 in every 100,000 Australians were diagnosed with invasive melanoma, compared to about 47 out of every 100,000 New Zealanders.’ I’m pleased to see that these incidence rates also seem to be decreasing in New Zealand. Even better news.

The current record holder is a changing feast. The most recent data presently available (from 2019) has the annual rate for both countries both at about 36 per 100,000.

In case you’re interested in how these incidence rates compare with other countries, they’re shown below (from a 2022 Assessment) for the 20 countries with highest and lowest rates. Those rates from New Zealand look a little low when compared with the plot above, but you get the general picture. Note the different scale in the upper and lower segments. The highest rates (New Zealand and Australia) exceed the lowest by more than a factor of 100.

Thankfully, the mortality rate for both countries is much lower, by around a factor of 10 in Australia (and also dropping). Currently, Australia’s age-adjusted annual mortality rate is about 6 per 100,000 per year. It’s little higher in New Zealand. We’re the current unwanted holders of the world-record rates for death from melanoma.

If you’re going to be diagnosed with melanoma, my advice is to be in Australia rather than New Zealand.

… and get it diagnosed EARLY!