Skin cancers

‘Robust discussion’ needed on diagnostic thresholds for melanoma in situ and dysplastic naevus


Dermatologists may need to rethink diagnostic thresholds for melanoma in situ and dysplastic naevus, Australian researchers suggest, after finding the current criteria may lead to inconsistent diagnoses and overdiagnosis.

A review of 14 diagnostic reproducibility studies found clinicians often disagreed with each other and themselves about a lesion’s identity. The largest study found pathologists and an expert panel consensus agreed on MPATH-Dx class III-based diagnoses just 40% of the time, with inter- and intra-observer discord rates of 55% and 40%, respectively.

Meanwhile, two other studies showed evidence of “diagnostic drift” over time, with more lesions labelled ‘malignant’ in recent years, Ms Caitlin Semarian, Research Assistant at the University of Sydney School of Public Health and her team wrote in the British Journal of Dermatology.

In 2008–2009, seven of 40 lesions considered severely dysplastic naevi or superficial spreading melanomas in 1988–1990 were upgraded to melanomas; none were downgraded, the authors wrote about one study.

The other, involving 1,179 junctional or compound naevus diagnoses from 1980–1989 saw 10% reclassified as dysplastic naevi in 2011–2012, based on contemporary histopathological criteria.

“These studies both suggest an implicit lowering of the diagnostic thresholds for melanoma and severely dysplastic naevus over time, causing expansion of the disease definition,” the authors wrote.

The changes may lead to overdiagnosis — inflating melanoma incidence and putting patients at unnecessary risk of psychological and physical harms, the authors suggested.

“Many countries have seen a dramatic increase in the reported incidence of cutaneous melanoma in recent decades, largely driven by increased diagnoses of melanoma in situ and thin invasive melanoma,” they wrote.

While ageing populations could account for some true growth, “much of this increase may represent overdiagnosis”.

As a result, patients may be burdened with procedures and long-term surveillance for lesions that “would never have caused harm if left undetected or untreated”, while the healthcare system sustains significant costs, the authors wrote.

In a natural history study, less than 4% of lentigo maligna progressed to maligna melanoma per year, they noted.

Further, none of the 127 patients with positive or close margins in three other studies developed invasive melanoma at the severely dysplastic naevus site, or metastases after six months to 30 years’ follow-up.

“The sparse natural history evidence suggests uncertain but likely low risk of progression from melanoma in situ to invasive melanoma, and negligible risk of progression from severely dysplastic naevus to invasive melanoma,” Semarian and co wrote.

Therefore, “these types of lesions may be better conceptualised as risk factors for, rather than obligate precursors to, invasive melanoma.”

As a result, the authors called for “robust discussion” about the appropriateness of existing criteria and the implications of updating it to prevent further overdiagnosis.

“Such discussions could be facilitated through an international summit on the topic, which would inform next steps towards achieving change in policy and practice for pathology diagnosis,” they concluded.

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