Risk factors for skin cancer

Before you even pick up the dermatoscope, you already have information that shapes how you interpret what you see. A patient's risk profile changes the pre-test probability of malignancy — and that matters for every lesion you assess.

Ultraviolet exposure

Cumulative UV exposure is the single most significant modifiable risk factor for skin cancer. This includes both chronic occupational exposure (outdoor workers, farmers, builders) and intermittent intense exposure (sunburn history, particularly in childhood and adolescence). A history of sunbed use also increases risk significantly.

Ask about outdoor occupations, sun-seeking behaviour, sunburn history, and sunbed use. Patients may not volunteer this information unless asked directly.

Family history

A first-degree relative with melanoma approximately doubles an individual's lifetime risk. Multiple affected family members, or a family history of familial atypical mole syndrome, increases risk further.

Family history of non-melanoma skin cancer (basal cell carcinoma, squamous cell carcinoma) is also relevant, though the risk increase is more modest.

Previous skin cancer

A personal history of any skin cancer is one of the strongest predictors of future skin cancer. Patients who have had one melanoma have a significantly increased risk of a second primary melanoma. Similarly, patients with a history of BCC or SCC are at elevated risk of further lesions.

Skin phototype

Fair skin that burns easily and tans poorly (Fitzpatrick phototypes I and II) carries a higher risk of all skin cancers. However, skin cancer occurs across all phototypes, and melanoma in darker skin is often diagnosed later — partly because of a false assumption that darker skin is protective.

Immunosuppression

Patients on immunosuppressive therapy — organ transplant recipients, patients on long-term corticosteroids, those receiving biologic therapies — have a markedly increased risk of skin cancer, particularly squamous cell carcinoma. Transplant recipients may have a 60 to 100-fold increased risk of SCC.

High mole count

A total body naevus count above 50 is an independent risk factor for melanoma. Patients with numerous naevi also present a practical challenge: there are simply more lesions to assess, and the "background noise" of benign naevi can make it harder to spot the one that is different.

This is where the ugly duckling sign becomes particularly valuable — the lesion that does not look like the others.

Changing lesion history

Perhaps the most important risk factor of all: the patient telling you that a lesion has changed. New growth, change in colour, change in shape, change in size, bleeding, itching, or crusting — any of these should be taken seriously, even if the dermoscopic appearance is not obviously concerning.

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