Skin cancers

QSkin: is melanoma screening leading to overdiagnosis?

Physician-based skin cancer screening across Australia would identify about 6,400 additional melanomas each year, Queensland research suggests.

According to data from the QSkin Study, people undergoing physician-based screening for skin cancer have melanoma detection rates at least 29% higher than those not undergoing screening.

However the researchers, from the QIMR Berghofer Medical Research Institute, Brisbane, are questioning whether those mostly in situ lesions would represent overdetection.

Their study, published in the British Journal of Dermatology, comprised 38,682 Queenslanders 40-69 years with no prior history of melanoma. Almost three-quarters (73%) of the cohort reported a skin examination by a doctor in the 3 years before enrolment.

During follow-up, 967 participants were newly diagnosed with at least one melanoma (316 with invasive melanoma only, 586 with in situ melanoma only, 65 with both).

“The age-standardised incidence of melanoma among those who reported a prior skin examination was 2.2-fold higher than in those with no prior skin examination (incidence rate ratio 2.21, p<0.001),” the study said.

“The age-standardised rate of biopsies was 4.0-fold higher among those who had a prior skin examination than those who did not (incidence rate ratio 4.00, p<0.001).”

After propensity score weighting for observed risk factors, the study found significantly higher rates of melanoma (aHR 1.29, 95% CI 1.02 – 1.63) and subsequent biopsies (aHR 1.85, 95% CI 1.69 – 2.04) among those who had undergone physician skin examination prior to enrolment.

“In separate analyses of invasive and in situ melanoma, the higher risk associated with skin examination was evident only for in situ melanoma (adjusted HR in situ 1.45, 95% CI 1.09 – 1.92; adjusted HR invasive 1.05, 95% CI 0.72-1.54).”

“We estimated the absolute risk of melanoma at 5 years in the screened and unscreened groups to be 0.0194 and 0.0145 respectively, generating a risk difference of about 0.5% at 5 years. This equates to a number-needed-to-screen to detect one excess melanoma of about 206.”

Led by medical epidemiologist Professor David Whiteman, the researchers said the higher rates of biopsies and melanoma among screened patients suggested overdiagnosis.

The findings were also consistent with reports in the literature of rapidly rising incidence of in situ and very thin invasive melanomas.

“In summary, these data lend plausibility to the argument that overdetection is occuring among the section of the population undergoing skin screening,” they said.

Speaking to the limbic, Professor Whiteman said screening was predicated on the longstanding belief that if melanomas were found early, before they became invasive, patients will have a better prognosis.

“When you have a thin melanoma, a level 1 melanoma, your prognosis is much better than if you have a level 2, 3 or 4. So there is a clear benefit in finding melanomas early. None of that changes,” he said.

“But what has been happening in the background in Australia, is there has been an increase in vigilance and diligence among GPs and doctors in general to examine people’s skin.”

He said it was inevitable that some of the detected lesions, excised and diagnosed as melanoma, would have remained undetected without screening and never caused a problem.

“This is not unique to melanoma at all; it’s been known about in cancer screening now for 20-30 years. Wherever we do screening programs, we find this phenomenon that the more you look the more you find but not always are the ones you find destined to be harmful.”

“At least in Queensland, it looks like about 29% of melanomas diagnosed are occurring in people who have been screened and probably those wouldn’t have been diagnosed if they hadn’t had their skin systematically examined.”

“If it was 1% or 2% you’d ignore and live with that. But when it’s up to nearly a third of melanomas, it’s not ignorable anymore.”

He said overdetection had psychological and financial costs on people.

“When we launch vigorous campaigns to encourage people to come and get their skin checked we are going to find more and more cancer but some of them were never going to hurt people.”

“This is not to stop screening, not to even defer or delay anyone from attending, it’s really a message for the medical community to say we need to move to a point in the future where we have even better diagnostic ability to discriminate those that are truly harmful from those that are more likely to have an indolent course and are less likely to cause any long term problems.”

He speculated that point of care diagnostics, perhaps a combination of molecular and immunological assays, would in the future be able to discriminate between the different lesion types.

“If there was a better way of us diagnosing which ones are harmful and which ones aren’t, we would be doing everyone a service. We don’t have that capability right now …but knowing that these lesions are out there and they are a sizeable proportion of the total pool of melanoma, it’s a reasonable target to aim for.”

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