The importance and pitfalls of melanoma screening

You would think melanoma screening and diagnosis would be straightforward – after all, the skin is your most visible organ and doesn’t need surgery, endoscopes or x-rays to examine.

Early detection of a melanoma allows it to be easily removed before it spreads. Compared to treating advanced metastatic melanoma, excisions from the skin are cheap, quick and avoid the potentially serious side-effects of drug treatments for metastatic melanoma. This makes mass screening an appealing approach, especially in vulnerable populations in high-UV places like Australia.

But mass screening, whether organised or opportunistic, does have serious drawbacks. Even Australian general practitioners, who have regular experience with melanoma due to Australia’s high per-capita incidence, excise 20 benign lesions for every melanoma – the international average is 29 to 1. On top of this, it’s also been estimated that over 50% of melanomas in Australia are over-diagnosed. These are real cancers, but so slow-growing that they would never have caused a problem. An appropriate level of screening matches an increase in early detection with a decrease in advanced disease, but with overdiagnosis there are many more melanomas detected with no overall decrease in metastatic disease and death.

We can’t yet tell these overdiagnosed melanomas apart from early melanomas with the potential to become invasive, so they must be excised, but this leaves patients with scars and medical costs, not to mention the anxiety that comes when you’re told you have cancer. In Australia, there are over 45,000 melanomas diagnosed each year, including 29,000 in situ (very thin) melanomas, so thousands of people are affected by overdiagnosis. It also means we are pouring health budget money into screening that isn’t clinically effective and could do more good elsewhere.

These considerations have led some researchers to advocate for an end or steep reduction to screening, but that’s a risky strategy for patients. Researchers from several countries independently examined the Breslow thickness – the thickness of a melanoma from the skin surface to its deepest point – in patients diagnosed in 2019 and patients diagnosed after COVID lockdowns. Despite urging from health officials for people to continue with regular health appointments during lockdowns, many people misunderstood or chose to avoid their usual check-ups. As a result, average melanoma thickness rose significantly, from 0.88mm to 1.96mm in one study. That might not sound like much, but it has a real impact on your chances of long-term survival.

A certain amount of overdiagnosis is inevitable in a health system that is committed to preventing advanced cancers by screening for early cancers, and modelling shows that we do prevent many advanced cancers with screening. However, new technologies, like iToBoS’s whole body imaging with AI clinician support and personalised risk scores, will help us to reduce the number of unnecessary excisions. So will ongoing research into who is accessing opportunistic screening and why, and whether a targeted, risk-based screening program rather than a population-wide program is more cost-effective.