Scalp melanoma – clinical and histological features, prognosis and mortality

Background: It is well known that there are site-specific differences in melanoma characteristics and prognosis. Scalp melanoma has been described to have a worse prognosis than melanoma elsewhere, though the reasons for this are poorly understood. Furthermore, the clinical and histological features of scalp melanoma are not well described. Objectives: This thesis aims to describe the features of scalp melanoma (including epidemiology, clinical presentation, histological characteristics and patient survival), to determine if there are any differences between these features and features of other head and neck melanoma, and to determine if scalp location is independently associated with survival in cutaneous head and neck melanoma. Methods: Firstly, a narrative review was conducted examining all existing literature on scalp melanoma. Secondly, a cross-sectional study was conducted of all cases of cutaneous head and neck melanoma seen at a multidisciplinary melanoma clinic in Melbourne, Australia over 20 years; clinical and histological features of all scalp melanoma cases were compared with other cutaneous head and neck melanoma cases. Finally, a retrospective cohort study was undertaken of all patients with invasive cutaneous head and neck melanoma seen at the same clinic over the same period, with follow-up mortality data obtained; survival of all scalp melanoma cases were compared to survival of other cutaneous head and neck melanoma cases, and multivariable survival analysis performed. Results: Invasive scalp melanoma was associated with male sex, increasing age, amelanosis, rapid growth rate, and being noticed by a person other than self, relative/spouse or doctor. Histologically, scalp melanoma had greater Breslow thickness than melanoma elsewhere in the head and neck, and was independently associated with satellite metastases, nodular and desmoplastic subtypes. Scalp melanoma had poorer overall and melanoma-specific survival compared to other cutaneous head and neck melanoma, but after taking into account patient age, sex and tumour histological features, scalp location was no longer associated with survival. Conclusions: Scalp melanoma appears to be clinically and histologically distinct from other head and neck melanoma. It occurs in predominantly in older men, is frequently non-pigmented, rapidly-growing, and is often overlooked by patients, their families and doctors. Not only should clinicians routinely examine the scalp for melanoma, they should also adjust their diagnostic criteria to accommodate this distinctive spectrum of clinical presentation. Due to the increased frequency of high risk histological features in scalp melanoma, careful histological assessment of scalp melanoma excision specimens is required.. Scalp melanoma patients had poorer survival than patients with other head and neck melanoma, which may be explained by tumour Breslow thickness and higher proportion of male patients.