Malignant melanoma

What is malignant melanoma?

Cancerous growth of melanocytes results in melanoma. 90% of melanomas are cutaneous but malignant melanomas have been described in nearly every organ of the body. Non-cutaneous melanomas are rare.¹

See the separate Malignant melanoma of skin article.

See the separate Choroidal melanoma article.

• The most common form of melanoma in the central nervous system (CNS) is metastases of cutaneous melanoma. Melanoma has the highest risk of spread to the CNS among all common cancer types. More than 60% of patients with malignant melanoma will develop brain metastases, with higher risks if the primary tumour was on the head, neck or trunk, the BRAF mutation is present (present in 40% of malignant melanomas), ² the primary tumour was deep, ulcerated or invasive or where the melanoma also has metastasised to other organs. ³

• Brain metastases due to malignant melanoma most commonly present with headaches (40-50%) whilst 20-40% present with focal neurological symptoms.²

• Prior to 2000, the prognosis for brain metastases arising from malignant melanoma was poor with a 3-4 month mean survival and a one-year survival of < 10%. This has improved with developments in radiotherapy and immunotherapy. One-year survival is now around 50% and two-year survival around 27%.²

• Primary intracranial malignant melanoma (PIMM) arise from leptomeningeal melanocytes.

• Primary intracranial melanomas account for 1% of all malignant melanomas and 0.07% of intracranial tumours. ⁴

• Prognosis for primary intracranial melanoma is poor with a mean survival of 22 months. ⁵

• There is limited evidence for treatment for primary intracranial melanomas. Currently radical resection with radiotherapy possibly increases survival but targeted immunotherapy is likely to offer the most hope in the future. ⁵

• Mucosal melanoma present in the anorectum, nasal cavity, genitourinary tract, upper gastrointestinal tract and maxillary sinus.

• Mucosal melanomas make up 1% of all malignant melanomas.

• Risk factors are less well known but include cigarette smoking, denture irritation, alcohol, chronic infections caused by microorganisms and mechanical stress generated by routine activities.

• They tend to be aggressive with a poorer prognosis than cutaneous malignant melanomas (10-20% 5-year survival compared with 93% for cutaneous).

• One of the reasons for this is that they tend to be diagnosed at a later stage. ⁷

• Radical tumour excision remains the first line treatment. ⁸

• Targeted immunotherapy is likely to be the most successful treatment but, to date, mucosal melanomas are showing a lower response than cutaneous melanomas. ⁸

See also the separate Carcinomatosis article.

• No primary lesion is identified in 3% of patients presenting with palpable evidence of regional metastatic melanoma.⁹

• Patients with occult primary melanoma may present with a solitary metastasis, lymph node disease, or systemic disease. It is diagnosed when, despite thorough physical examination and revision of previous histology, no primary cutaneous, ocular, or mucosal melanoma can be found.⁹

• All patients should be staged. MUP is classified as stage III when lymph node or skin/subcutaneous metastases are present and as stage IV when there is visceral involvement. ¹⁰

• Immunotherapy and targeted therapy have improved the prognosis but it remains difficult to predict efficacy. ¹⁰