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Eyeballing skin cancer not good enough for accurate diagnosis, say experts

But dermoscopy may help GPs make appropriate referrals, finds Cochrane review

Caroline White

Tuesday, 11 December 2018

Inspecting a suspicious skin lesion using the naked eye alone or relying on smartphone apps are not enough to accurately diagnose skin cancer, a group of experts have concluded following a large scale systematic review* of the available published research.

But dermoscopy- a technique using a handheld device to zoom in on a mole and the underlying skin- is better than visual inspection alone, and may also help GPs to correctly identify those who need to be referred to a specialist, finds the Cochrane Review.

The review is part of a Special Collection of 11 Cochrane Systematic Reviews bringing together a large body of research on the accuracy of different tests used to diagnose all types of skin cancer.

“Early and accurate detection of all skin cancer types is essential to manage the disease and to improve survival rates in melanoma, especially given the rate of skin cancer world-wide is rising,” commented Dr Jac Dinnes, of the University of Birmingham’s Institute of Applied Health Research, who led the suite of 11 reviews.

“The visual nature of skin cancer means that it can be detected and treated in many different ways and by a number of different types of specialists, therefore the aim of these reviews is to provide the world’s best evidence for how this endemic type of cancer should be identified and treated.

“We have found that careful consideration should be given of the technologies that could be used to make sure that skin cancers are not missed, at the same time ensuring that inappropriate referrals for specialist assessment and inappropriate excision of benign skin lesions are kept to a minimum.”

Melanoma and cutaneous squamous cell carcinoma (cSCC) are high-risk skin cancers with the potential to spread and kill. A basal cell carcinoma (BCC) rarely spreads, but can infiltrate and damage surrounding tissue.

Key findings of the special collection were that visual inspection using the naked eye alone is not good enough and melanomas may be missed.

Smartphone apps used by people with concerns about new or changing moles or other skin lesions have a high chance of missing melanomas.

When used by specialists, dermoscopy is better at diagnosing melanoma than visual inspection alone, and may also help in the diagnosis of BCCs as well as possibly helping GPs to correctly identify people with suspicious lesions who need to be seen by a specialist.

Dermoscopy is already widely used by dermatologists to diagnose melanoma but its use in primary care has not been widely evaluated, and more specific research is needed, says the collection.

Checklists to help interpret dermoscopy might improve the accuracy of diagnosis for practitioners with less expertise and training, it suggests.

Remote specialist assessment of skin lesions (teledermatology) using dermoscopic images and photographs is likely to be a good way of helping GPs to decide which skin lesions need to be seen by a skin specialist, but future research needs to be better designed, says the collection.

Artificial intelligence techniques, such as computer-assisted diagnosis (CAD), can identify more melanomas than doctors using dermoscopy images. But CAD systems also produce far more false positive diagnoses than dermoscopy and could lead to considerable increases in unnecessary surgery.

Further research is needed on the use of specialist tests such as reflectance confocal microscopy (RCM) – a non-invasive imaging technique, which allows a clinician to do a ‘virtual biopsy’ of the skin and obtain diagnostic clues while minimising unnecessary skin biopsies.

RCM is not currently widely used in the UK, but the evidence suggests that RCM may be better than dermoscopy for the diagnosis of melanoma in lesions that are difficult to diagnose.

Other tests, such as using high frequency ultrasound show promise, particularly for the diagnosis of BCCs, but the evidence base is small and more work is needed, conclude the researchers.

Cochrane Skin Group founder Professor Hywel Williams, of the Centre of Evidence-Based Dermatology at the University of Nottingham, said: “Apart from a few exceptions, I was surprised by how poor the overall study designs were, especially in terms of accurately documenting where on the clinical pathway patients were tested.

“Although some useful conclusions have emerged, for example, on the role of dermoscopy, the greatest value of the research is to serve as a yardstick for designing future studies evaluating skin cancer diagnosis techniques on patients who are typically seen in GP and specialist settings.”

The research team said that future studies evaluating diagnostic skin cancer tests should recruit patients with suspicious skin lesions at the point where the test under evaluation will be used in practice.

Further research is also needed to evaluate whether checklists to assist diagnosis by visual inspection alone can improve accuracy and to identify how much accuracy varies according to the level of expertise of the clinician doing the assessment, they conclude.

*Diagnosing skin cancer. Cochrane Special Collections, 6 December 2018.

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