AUSTRALIA can expect to remain a global “leader” in rates of skin cancers for the next couple of decades, according to researchers who have provided the first accurate accounting of keratinocyte cancers.
Led by Professor David Whiteman, senior scientist and group leader of the Cancer Control Group at QIMR Berghofer, the researchers used a dataset of over 1.7 million patients – a 10% random sampling of the Medicare database, analysed for keratinocyte cancer treatments (identified by eight specific Medicare Benefits Schedule item codes) during 2011–2014. Histological data from the QSkin prospective cohort study were analysed to estimate basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) incidence.
“These cancers are the only cancers in Australia that are not counted in a systematic way,” Professor Whiteman told MJA InSight.
“Keratinocyte cancers – BCCs and SCCs – are very common cancers and we didn’t have the capacity to manually count all of those cancers. So, we’ve never really had a good handle on how common they are.”
Now we do, and the news is not good, particularly for Queenslanders.
The results, published in the MJA, showed that the person-based incidence of keratinocyte cancer excisions in Australia was 1531 per 100 000 person-years between 2011–2014.
“That’s exceptionally high compared with [other nations],” Professor Whiteman said in an exclusive podcast with MJA InSight.
In Queensland, the keratinocyte cancer incidence climbed to 2679 per 100 000 person-years, New South Wales and the ACT were at the national average of 1495 per person-years, while Victoria and Tasmania were below the average at 966 person-years.
“It’s a latitude gradient,” Professor Whiteman said. “The closer to the equator, the higher the rates of these types of cancers.”
Whiteman and colleagues found that incidence increased with age, and was higher for men than women (standardised incidence ratio, 1.43; 95% CI, 1.42–1.45). Lesion-based incidence was 3154 per 100 000 person-years. The estimated aged standardised incidence rates for BCC and SCC were 770 per 100 000 and 270 per 100 000 person-years respectively. During 2011–2014, 3.9% of Australians had one keratinocyte cancer excised and 2.7% had more than one excised; 74% of skin cancers were excised from patients who had two or more lesions removed. Multiplicity was strongly correlated with age; most male patients aged over 70 years were treated for multiple lesions. Keratinocyte cancer incidence was eight times as high among people with a prior history of excisions as among those without.
And the hits keep coming, with rates not expected to begin dropping for another couple of decades as the pre-Slip, Slop, Slap generation grow older and their damaged skin cells develop into keratinocyte cancers.
“The Slip, Slop, Slap campaign really started in earnest in 1981,” Professor Whiteman said. “Those born then or slightly before have had the benefit. And we can see that in people in their 40s where the rates of BCCs and SCCs are going down.
“[Keratinocyte cancers] are a disease of older people. Those people in their 50s, 60s and 70s didn’t get the benefits of the campaigns and therefore we can expect another couple of decades of very, very high rates.
“Then, hopefully, we will start to see rates declining.”
Keratinocyte cancers present unique difficulties for GPs, Professor Whiteman said, complicated by the fact that patients often lump them in with melanomas, making it difficult to take an accurate history.
“The popular misconception is that [keratinocyte cancers] are trivial cancers,” Professor Whiteman said.
“In one sense there is some truth to that, particularly for BCCs because they are very rarely metastatic. Whereas SCCs are more aggressive in that they can metastasise and can kill people.
“But they’re not trivial in the sense that many, many people are affected and quite a number of those people are affected quite severely.
“If they go untreated they can continue to grow and, in the case of SCCs, they can certainly spread. So, they’re not trivial cancers, but that’s often how people think of them, because if they’re treated early, they can be treated very effectively in a GP’s surgery.
“People often call them all a melanoma, which makes it very hard for GPs to take an accurate history. When asked if they have a history of melanoma, many patients say yes, but when you check the records you find they’ve actually had a BCC or an SCC.”
The take-home message for GPs?
“Once a patient has had any type of keratinocyte cancer, there is a strong likelihood that they’ll have more,” Professor Whiteman said. “That makes follow-up and surveillance very important.”
The good news is that although keratinocyte cancer incidence was eight times as high among people with a prior history of excisions, strict sun protection “can delay the onset of a new one, and even prevent it developing entirely”, said Professor Whiteman.
“BCCs and SCCs will appear as a sore that doesn’t heal and they can take many different forms. The difficult ones are very difficult to diagnose,” he said.
“GPs need to have a high index of suspicion.”
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