Mucosal Melanomasspecial Considerations

Mucosal melanomas of the head and neck are rare, with only about 1000 cases reported. Of more than 84,000 melanoma cases in the National Cancer Data Base, only 1.3% were mucosal, and 55% of that subgroup arose in the head and neck (15). The majority of head and neck mucosal melanomas are sinonasal in origin, and the others are primarily from the oral mucosa. Among the sinonasal tumors, 81% arise in the nose and 19% in the sinuses, although the size of some of these tumors makes it difficult to be sure of the site of origin. Most of the oral lesions arise from the hard palate and maxillary alveolar ridge. Melanomas arising in other head and neck mucosal sites such as the larynx, pharynx, and cervical esophagus have been reported, but are quite rare. A melanoma arising in the oropharynx is shown in Figure 3. The oral lesions are often detected by healthcare personnel as a dark spot in the mouth, but the sinonasal lesions are often only apparent after symptoms such as epistaxis or nasal obstruction occur. The sinonasal melanomas are often polypoid, which makes measuring their thickness problematic. Conjunctival melanomas are also mucosal in origin, and may come to the attention of head and neck specialists, both for surgical resection and treatment of the lymph nodes at risk, which are primarily in the parotid gland. A conjunctival melanoma is shown in Figure 4.

Staging of mucosal melanomas is not addressed in the TNM system. A simple and practical system used by most clinicians classifies tumors with localized primary disease as Stage I, those with regional disease as Stage II, and those with distant disease as Stage III. About 70% of patients with head and neck mucosal melanoma present with Stage I disease, about 15 to 20 % present with stage II disease, and the remainder present with Stage III

FIGURE 4 Malignant melanoma arising from the conjunctiva. This patient required orbital exenteration and parotidectomy. He eventually died from distant disease.

disease. The incidence of lymph node metastases is higher in oral mucosal melanomas than in sinonasal melanomas, as might be expected based on the higher density of lymphatic channels in the oral soft tissues. In a review of 59 patients seen over a 20-year span at Memorial Sloan-Kettering Cancer Center, the only independent predictors of outcome were clinical stage, thickness greater than 5mm, vascular invasion on histologic examination, and development of distant disease (16).

The infrequent occurrence of mucosal melanomas of the head and neck makes it difficult to evaluate different treatment approaches. Most authorities agree that surgery plays a primary role, and that postoperative radiation therapy is indicated in most cases (17). Radiation therapy is almost always used as an adjunct in the sinonasal melanomas because of the difficulty in obtaining wide margins in this anatomic location. A recent multicenter cooperative study concluded that postoperative radiotherapy has a positive effect on outcome in sinonasal melanomas invading the skull base (18). The mucosal melanomas also have a propensity for submucosal spread, making it difficult for surgeons to estimate the true tumor margin. Frozen section analysis of melanomas and their surgical margins is often difficult, which further hampers intraoperative assessment of the adequacy of the resection, resulting in close or positive margins that mandate postoperative radiotherapy. Although some mucosal melanomas of the head and neck have been reportedly cured by radiation treatment alone, there is a general consensus that radiation therapy should be used as a postoperative adjunct in most cases, with primary radiotherapy being used for palliation or in those patients in whom surgery is contraindicated for medical reasons. Some have suggested that because of the poor outcome for late stage disease, radiation should be reserved only for patients with potentially curable early stage disease (19).

Diagnostic measures for mucosal melanomas are similar to those for cutaneous melanomas, although imaging may play a greater role in evaluating the primary site, especially for the sinonasal melanomas. Biopsy, MRI, or CT of the primary site, and staging with PET and/or CT of the brain, chest, abdomen and pelvis, are performed in almost every case. Special stains, such as S-100 protein and HMB 45, may be required to make a histologic diagnosis. Treatment consists of surgery, which should encompass the primary site with as wide a margin as is feasible without creating inordinate functional or cosmetic deficits. Cervical node management is controversial, as it is with cutaneous melanomas. Because of the rarity of mucosal melanomas of the head and neck, no series has been reported evaluating sentinel node biopsy in this subgroup of melanomas. Prophylactic treatment of the neck should be considered for most oral cavity melanomas, but not for sinonasal melanomas. As noted above, radiation should be given postoperatively to almost all patients with mucosal melanoma of the head and neck. Adjunctive treatment with chemotherapy and biological agents such as interferon introduces additional toxicity, and has not been shown to impact patient survival.

Local recurrences are common after surgery for head and neck mucosal melanomas, occurring in more than half of patients in most reports (16, 17, 19). Nevertheless, local recurrence does not appear to be a good predictor of outcome. Lymph node metastases occur in as many as 42% of patients with oral mucosal melanomas, and in 15-20% of patients with sinonasal melanomas. Lymph node metastases can be controlled with neck dissection and postoperative radiation (in selected cases), but overall salvage is poor. This appears to be related to the strong correlation between lymph node metastases and distant failure. Distant metastases are most commonly seen in the lung, brain, bones, and liver, and death ensues in a mean of 5 months. The median time to relapse is about one year, although late relapses beyond 5 years are not unusual, as are seen with cutaneous melanomas. Cure rates have not improved much over the last several decades, and, as with all melanomas, improvement in disease control will probably rest with development of an effective systemic therapy.

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