Unpacking the research around mole count and skin cancer risk.

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H. Peter Soyer, The University of Queensland and Richard Sturm, The University of Queensland

The sooner cancer is diagnosed, the better the chance it can be treated. This is why, when it comes to melanoma, doctors advise people to regularly check their bodies and look out for new moles or existing ones that have changed shape.

We have long known people who have many moles – as well as those with atypical moles – have a predisposition to melanoma.

But a paper published recently in the respected journal JAMA Dermatology has challenged that notion. The study’s authors surveyed more than 500 melanoma patients and found most of those with melanoma had few moles and no atypical moles.

This was surprising and led to headlines such as: “Moles are NOT the only sign of deadly skin cancer: Most melanoma patients ‘have fewer than 20 – and none that look dangerous’.”

But people with a lot of moles and those with atypical moles shouldn’t cancel their skin check appointments. What we have always known still stands.

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Experts consider those with more than 15 moles to be at higher risk of melanoma than those with under 15. But the JAMA study showed most melanoma patients had 0-20 moles, without specifying how many had over 15 and how many under. This is only one consideration to take away.

Let’s further unpack the study to see what it’s really saying.

How was the study conducted?

Researchers surveyed 566 patients with melanoma in the United States. They aimed to examine the number of total and atypical moles in patients newly diagnosed with melanoma.

They also wanted to explore whether there was a relationship between these measures and tumour thickness. Researchers controlled for a number of variables such as age, sex and melanoma subtype. There were six groupings of subtypes, including superficial spreading melanoma (SMM), which is the most common form.

Patients were examined within three months of diagnosis by two specialists, who classified them into groups based on their total number of moles, number of atypical moles and the thickness of their moles.

There were three groups for total mole count: 0 to 20 moles, 20 to 50, and greater than 50.

Atypical moles were also grouped into three: 0, one to five, or greater than five. And mole thickness, which is the most relevant prognostic marker for melanoma, was categorised into two groups: moles of 2.00 mm or less and moles 2.01 mm or greater.

What were the results?

The study’s overall and main conclusion was that most melanoma patients had fewer than 20 moles and no atypical moles.

Another finding was that patients under the age of 60 with thick melanomas were more likely to have fewer total moles, but more atypical moles.

The suggestion here was that physicians and patients shouldn’t rely on total mole count alone as a reason to perform skin examinations, or to determine a patient’s risk.

This is indeed an important finding and gives cause for people and doctors to not discount the risk if a patient has few moles. But the study had several points of weakness, which need to be taken into account when considering its findings.

 How should we read the findings?

To draw the conclusion that most melanoma patients have few moles or no atypical moles, the study would have needed to compare the melanoma patients with a group of volunteers without melanoma. This would show whether there was any meaningful difference between the two groups.

Past studies have found those with melanoma will generally have more moles and more atypical moles than the healthy group they are compared with.

Further, total mole count is more related to the risk of getting superficial spreading melanoma (SMM). But the authors grouped all melanomas together in their data. Had SMM patients been considered separately, there would likely have been fewer in the 0 to 20 mole category.

Perhaps the main weakness is the brackets of mole counts, which were too wide (0 to 20, 20 to 50) to be reliable indicators. Our unpublished research on melanoma patients from Queensland estimates that those with more than 15 moles have a 30% higher risk of melanoma than those with fewer than 15.

It isn’t clear how many patients in the 0-to-20 grouping had more than 15 moles. The results would have likely been more in line with previous research if the data outlined precisely how many moles each patient had. Of those patients with SMM, 61.6% had 0 to 20 moles. But 22.6% had 20 to 50, and 15.8% had more than 50. (Post continues after gallery.)

The fact over 40% had more than 20 moles is significant and underscores what we currently know to be true for melanoma risk.

In patients younger than 60, the study showed having more than 50 moles was associated with a sharply reduced risk of thick melanoma. Having more than five atypical moles was associated with thicker melanoma.

We could interpret this to mean patients who thought they were at lower risk from having few moles may have waited longer before seeking treatment. Those with more moles may have been more likely to spot changes quickly and obtain treatment earlier, resulting in less thick melanomas.

What else should we consider?

The JAMA paper authors say their findings raise questions about whether public health messages overstate the emphasis on mole numbers and atypical moles.

This is a dangerous statement, as it is precisely these factors that predict people at high risk of developing melanoma.

Those who are more at risk with high mole counts may come to believe they are less likely to have thick melanomas than those with few moles. This observation must be taken with caution as the findings could have reflected a greater vigilance of those at higher risk.

But the study also highlights that patients and their health care professionals should be equally concerned about melanoma risk in those with few moles. And this is important.

Public messages need to include other models of diagnosis, such as the one readily recognised by dermatologists. It acknowledges two pathways to melanoma, one based on sun-damaged skin and the other on mole counts.

 Peer Review.

The authors have identified the main issues in this study’s design. Firstly, it is a case series, which is accorded little weight when considering the role of potential risk factors in causing a disease.

Case series don’t have a reference sample of patients without the disease of interest, so it isn’t possible to infer whether those with disease differ in any meaningful way from those without it. The lack of a control group in this study makes it difficult to generalise the findings to the wider community, let alone to other countries such as Australia.

Similarly, there isn’t enough information about the group of participants used – whether they are typical of all patients with melanoma, or represent an unusual grouping. Were they referred from other specialist centres because they were challenging or unusual cases? We don’t know the answer to these questions, but they are important.

While the JAMA study provides doctors and patients with a timely reminder that not all people with melanoma have high mole counts, it doesn’t offer a solid basis for changing policy or practice just yet.

H. Peter Soyer, Professor of Dermatology, The University of Queensland and Richard Sturm, Principal Research Fellow, Dermatology Research Centre, The University of Queensland

This article was originally published on The Conversation. Read the original article.