Fiona M. Lewis Melanomas of the genital tract are not common but often present late and carry a poor prognosis, especially if the vagina is involved. Vulval melanoma constitutes between 2% and 4% of all female melanomas. It is the second commonest vulval malignancy [1], but accounts for only about 5% of malignant vulval neoplasms [2, 3]. Whereas the incidence of cutaneous melanoma continues to increase, the incidence of vulval melanoma has remained stable, and they are estimated to occur at a rate of 0.2/100 000 women per year [4]. The average age at diagnosis is in the mid‐60s, but melanomas have been reported in children, although this is exceptionally rare. Most patients are Caucasian but when it does occur in other racial groups, there is often a poorer prognosis [5]. A family history is found in 15% [1]. Mucosal melanomas have a different genetic profile from cutaneous melanomas, and vulval lesions seem to be a distinct group. The common mutations in cutaneous melanomas, BRAF and NRAS, are not common in vulval lesions, but c‐KIT mutations are higher, being found in 22% of cases as compared with only 3% in cutaneous melanoma [6, 7]. PD‐L1 mutations were found in 69% of vulval melanomas in one study [8], and mutations in KIT and TP53 have also been demonstrated in vulval melanoma [9]. The aetiology of vulval and vaginal melanoma is unknown as ultraviolet exposure cannot be implicated at this site. Only a small number are thought to arise from pre‐existing naevi. There are isolated cases reported in association with lichen sclerosus, especially in children [10–12], but it is not clear whether this is a causative factor. One study found 3 cases of lichen sclerosus in 33 patients with vulval melanoma [13]. They were all found in cases of in situ melanoma, but not in any invasive disease. The histology of vulval melanoma is similar to that elsewhere. The tumours are asymmetric and poorly circumscribed, often with an extensive junctional component. There is cytological atypia and Pagetoid spread (Figure 44.1). The in situ part can be subtle with only minimal atypia (Figure 44.2), but the invasive part is deep with atypical epithelioid or spindle tumour cell types [14]. Melanin can be focal or diffuse and may be absent. Ulceration and necrosis can be seen in large tumours. Immunohistochemistry is positive for S100, Melan A, and HMB 45. Atypical melanocytic hyperplasia, which is usually associated with chronic solar damage, was found in 15 of 36 genital tract melanomas, but the biological behaviour and significance of this is not clear [15]. Different histological staging grades have been used for vulval melanoma, and tumour depth is generally regarded as the most important, as for cutaneous melanoma. The Clark level, which defines the depth of the tumour in terms of dermal planes, is limited by the fact that many vulval melanomas are already Stage IV at presentation. The Breslow technique measures tumour thickness, and there is widespread agreement that this is a major prognostic factor and is generally used in staging [16]. The superficial spreading and lentiginous types are the ones most commonly seen on the vulva, whereas nodular melanoma is more common in the vagina. Figure 44.1 Ulcerated nodular melanoma. The initial presentation is often delayed, and 8% of patients with vulval melanoma present with advanced disease, compared with 2.7% in cutaneous melanoma [2]. Patients usually present with a relatively short history of, most commonly, a lump, although there may also be complaints of bleeding, pain, or itching. Some may have noticed a change in pigmentation. They can however be asymptomatic and found at routine examination. All areas of the vulva can be affected. A large retrospective study in Sweden has shown that the clitoris and labia majora were the most common sites, while almost half arose on the mucosa [4]. In this study, melanomas arose in pre‐existing naevi in 11 of 198 cases and only in hair‐bearing skin. The majority of these were superficial spreading in type rather than lentiginous. Lesions can be flat or nodular or a combination of both (Figure 44.3). If pigmented, they can be bluish or black, but many vulval melanomas can be partially or completely amelanotic (Figure 44.4). The most common type on the vulva is the superficial spreading type, whereas the nodular type is more common in the vagina [3
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Malignant Melanoma of the Vulva
Epidemiology
Genetics
Pathophysiology
Histological features
Clinical features
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