Dr Lisa Byrom ( left ) Consultant dermatologist , Mater Hospital Brisbane , Townsville University Hospital ; senior lecturer for the University of Queensland , Brisbane , Queensland .

Dr Hannah Gribbin ( right ) Dermatology registrar , Brisbane , Queensland .

First published online on 19 May 2023

BACKGROUND

MELANOMA is a malignancy of melanocytes

and is considered Australia ’ s ‘ national cancer ’; more than 17,000 Australians were expected to be diagnosed with invasive malignant melanoma by the end of 2022 . 1 GPs are at the forefront of the diagnosis of cutaneous melanoma .

The availability of adjuvant therapies for patients with metastatic melanoma places utmost importance on accurate diagnosis , staging and management of cutaneous melanomas .

This How to Treat covers the aetiology , classification and treatment of primary cutaneous melanoma , and aims to ensure GPs can confidently diagnose and initiate management for these tumours .

Epidemiology

Melanoma is predominantly a skin malignancy ( see figure 1 ), though can form primary tumours wherever melanocytes reside , including the eyes ( see figure 2 ), gastrointestinal tract , leptomeninges and oral / genital mucosal membranes . Queensland has the highest incidence of melanoma in the world , with an estimated 72 cases per 100,000 in 2021 . 1 Melanoma is the second most common cancer in men , and the third most common cancer

in women ( excluding non-melanoma skin cancers ). In Australia it is the most common cancer diagnosed in young adults , aged 15-24 . 1

The incidence of melanoma in situ in Australia continues to increase across all age groups ; however , after an intensive 30-year sun education campaign , the incidence of invasive melanoma in Australia is decreasing in those aged under 40 . 2 , 3

Several explanations have been offered for the rising incidence of melanoma in Australia , including increased screening with resulting detection of more indolent lesions , and inconsistency in histologic analysis of early evolving lesions . However , this does not explain the increase in melanoma mortality rates , particularly in older males .

Melanoma remains a significant health burden in Australia , with the age-standardised mortality rate estimated to be four deaths per 100,000 persons in 2021 . 1

Aetiology and risk factors

THE development of melanoma is

multifactorial and results from an interplay of genetic susceptibility and environmental exposure . Clinical and epidemiological experience

show that there are likely two pathways to the development of melanoma , described by the ‘ divergent pathway ’ model . 4 , 5 This model proposes that individuals with a lower propensity to developing naevi require a greater degree of sun exposure to promote the formation of melanoma . 4 , 5 Conversely , in patients with high naevus counts , less sun exposure is required to drive the development of melanoma . Patients with melanoma can thus be stratified into two groups ( see box 1 ).

The well-recognised risk factors for the development of melanoma appear in box 2 .

UV radiation

A causative role for UV radiation ( UVR )

in development of melanoma is best demonstrated by the geographic incidence of melanoma , adjusted for skin type , and being highest in regions closest to the equator . In addition , the incidence of melanoma decreases proportionally with increasing distance from the equator and , therefore , lower levels of UVR exposure . 7

Intense , intermittent UVR exposure appears to be the most significant in terms of melanoma risk . This hypothesis is supported by a systematic review demonstrating

Box 1 . Stratification of patients with melanoma

• Low naevus count / high sunlight pathway .

• High naevus count / low sunlight pathway .

Box 2 . Well-recognised risk factors for melanoma

that • UVR sunburn exposure in childhood ( including or ado- blistering childhood sunburns ).

• Individual phenotypic traits ( lighter skin complexion , red hair , blue eyes ).

• High number of naevi .

• Family history of melanoma .

• Personal history of melanoma .

• Older age .

• Immunosuppression . Source : Curiel-Lewandrowski CA , et al 2022 6

lescence was strongly associated with increased risk of melanoma . 8 In addition , melanoma is common on body sites that undergo intense , intermittent sun exposure ( such as the back in men and the backs of the legs in women ). 9 The use of