Skin cancer: what the evidence says about screening and spotting melanoma

Skin cancer is the most commonly diagnosed cancer in the United States, and also one of the most misunderstood, because "skin cancer" bundles together diseases with wildly different stakes. Getting the distinctions right matters, because they explain why there is no routine screening programme for a cancer this common — and where the evidence says attention actually belongs.

Three cancers, very different risks

The two most common skin cancers are basal cell and squamous cell carcinoma. They are frequent but, as the US Preventive Services Task Force puts it, infrequently lead to death or substantial morbidity [s1]. Melanoma is the outlier: it represents about 1 percent of skin cancers but causes the most skin cancer deaths [s1]. So the common skin cancers are rarely deadly, and the deadly one is uncommon — a pattern that shapes everything about how the disease is approached.

Melanoma risk is also unevenly distributed. It is about 30 times more common in White people than in Black people [s1]. But that statistic carries a trap: people with darker skin are often diagnosed at a later stage, when the disease is harder to treat [s1], so lower incidence does not mean no risk, and skin cancer is not a concern confined to fair-skinned people. Melanoma is among the cancers whose incidence has been rising in recent US data [s3].

Why there is no routine screening

Given how common skin cancer is, an obvious question is why there is no recommendation to have every adult's skin checked periodically. The answer is that the evidence to support it does not exist. In 2023 the Task Force concluded that the current evidence is insufficient to assess the balance of benefits and harms of a clinician performing a visual whole-body skin examination to screen for skin cancer in asymptomatic adolescents and adults — an "I statement" [s1]. That is not a finding that screening is harmful, nor that it is useless; it is a finding that the studies needed to weigh the benefits against the harms — such as unnecessary biopsies and overdiagnosis — have not been done.

An I statement is easy to misread. It applies specifically to routine screening of people with no symptoms and no history of skin lesions. It says nothing about people who notice a change in their skin, who are a different situation entirely.

What the warning signs actually are

Because population screening is unproven, early detection leans on recognising a suspicious lesion — and here the evidence is more useful. Early diagnosis improves melanoma prognosis [s2], which is why the features that distinguish a worrying mole are worth knowing. Clinical prediction rules used in practice, reviewed systematically, are built around exactly those features: asymmetry, an irregular border, more than one or an uneven distribution of colour, and a larger diameter, greater than 6 millimetres [s2]. The most-studied dermoscopy version of that rule, used by clinicians, had a pooled sensitivity of 0.85 (95% CI 0.73 to 0.93) and specificity of 0.72 (95% CI 0.65 to 0.78) [s2] — good, but not perfect, which is part of why suspicious lesions are biopsied rather than judged by eye alone.

For a member of the public, the practical translation is simpler than any checklist: a new mole, or an existing one that is changing in size, shape or colour, or that looks different from a person's other moles, is a reason to see a clinician. That is a prompt to seek assessment, not a self-diagnosis; most changing moles are not cancer, and only a clinician can tell.

Prevention is where the certainty is

If screening is unproven and warning signs are imperfect, prevention is where the evidence is strongest. Ultraviolet radiation is one of the established, modifiable causes of cancer [s4], and it is the dominant driver of skin cancer risk. Reducing UV exposure — through shade, clothing, and sun protection, and by avoiding indoor tanning — addresses the cause directly, which is a more certain lever than trying to catch the disease after it starts.

What this means for a reader

The evidence supports a clear division of labour. There is no proven benefit from routine whole-body skin screening for people without symptoms [s1], so the emphasis falls on two things: limiting UV exposure, which attacks the main modifiable cause [s4], and getting any new or changing skin lesion looked at promptly, because melanoma is far more treatable when caught early [s2]. People at higher risk — those with many atypical moles, a personal or family history of melanoma, or prior skin cancer — are in a different category, and how often their skin should be examined is a matter for a clinician.

Sources

• [s1] Screening for Skin Cancer: USPSTF Recommendation Statement, JAMA, 2023-04-01
• [s2] Diagnosing malignant melanoma in ambulatory care: a systematic review of clinical prediction rules, BMJ Open, 2017-03-06
• [s3] Cancer statistics, 2024, CA: A Cancer Journal for Clinicians, 2024-01-17
• [s4] Proportion and number of cancer cases and deaths attributable to potentially modifiable risk factors in the United States, CA: A Cancer Journal for Clinicians, 2017-11-21