Introduction: Nodular melanoma (NM) can be a challenging melanoma subtype for clinicians to diagnose due higher rates of amelanosis compared to superficial spreading melanoma (SSM) and lack of conformity to established ABCDE diagnostic criteria1-4. Behaviour of NM is distinct from other melanoma subtypes with a high vertical growth rate leading to a greater thickness at diagnosis and overall increased metastatic potential and elevated risk of death5, 6. There is a current lack of published information with respect to typical anatomical subsite and patient characteristics for nodular melanoma.
Method: A prospectively collected cohort of patients reviewed at a state-wide tertiary referral service for melanoma between 1994 and 2016 had all melanoma pathology reviewed by expert dermatopathologists. Patient characteristics were collected by clinician examination and review of each patient.
Main findings: Amongst 4270 total cases of invasive cutaneous melanoma, 661 (15%) NM were identified. Sixty percent of diagnosed NM were in males with an overall mean age of 67 years. In 86% of patients their NM was their first diagnosis of melanoma. Median Breslow thickness of NM was 2.8mm with 52% ulcerated. The mean mitotic count was 7/mm2. 14% of NM were associated with a pre-existing naevus. 27% of NM were diagnosed in the head and neck region, 25% on both legs, 19% on arms and 18% on the upper back. Nearly one quarter (23%) were clinically amelanotic. Lymphovascular invasion was detected in 8% of NM. Sixty percent of patients recalled more than one episode of severe sunburn, 53% had less than 50 total naevi with 78% having no clinically dysplastic naevi. The majority (63%) of NM patients had no previous diagnosis of non-melanoma skin cancer. Seventy two percent of patients were of Fitzpatrick skin phototype 1 and 2. Median Breslow thickness was 3.6mm in chronically high sun exposed sites and 2.5mm in less sun-exposed sites with a statistically significant Wilcoxon rank-sum test between sun and non sun-exposed sites (<0.001).
Principal conclusions and implications for the field: We describe an Australian cohort of patients diagnosed with nodular melanoma. This insight adds to our understanding of nodular melanoma in Australia, particularly with reference to novel data on patient characteristics and anatomical location to identify sites/patients at risk of this aggressive and challenging to diagnose melanoma.