A.O. Adisa1, W.O. Olawole2 and O.F. Sigbeku1
- Department of Oral Pathology, University College Hospital, Ibadan.
- Department of Oral and Maxillofacial Surgery, University College Hospital, Ibadan.
Malignant melanomas of the mucosal regions of the head and neck are extremely rare neoplasms accounting for less than 1% of all melanomas. Approximately half of all head and neck melanomas occur in the oral cavity. Less than 2% of all melanomas lack pigmentation, in the oral mucosa however, up to 75% of cases are amelanotic. No etiologic factors or risk factors have been recognized for oral melanomas. Some authors have suggested that oral habits and self medication may be of etiological significance. Oral melanoma is rare but it is relatively frequent in countries like Japan, Uganda, and India. It is rarely identified under the age of 20 years. In Australia where cutaneous melanomas are relatively common primary melanoma of the oral mucosa is rare. The surface architecture of oral melanomas ranges from macular to ulcerated and nodular. The lesion is said to be asymptomatic in the early stages but may become ulcerated and painful in advanced lesions. The diagnosis of amelanotic melanoma is more difficult than that of pigmented lesions. The neoplasm consists of spindle-shaped cells with many mitotic figures and no cytoplasmic melanin pigmentation. Immunohistochemistry using S-100, HMB-45, Melan-A and MART-1 will help in establishing the correct diagnosis. Radical surgery with ample margins and adjuvant chemotherapy are appropriate management protocol for malignant melanoma. Oral melanoma is associated with poor prognosis but its amelanotic variant has even worse prognosis because it exhibits a more aggressive biology and because of difficulty in diagnosis which leads to delayed treatment.
Keywords: amelanotic melanoma, oral cavity
Dr. A.O. Adisa
Dept. of Oral Pathology
University College Hospital
Malignant melanomas of the mucosal regions of the head and neck are extremely rare neoplasms accounting for less than 1% of all melanomas1. Approximately half of all head and neck melanomas occur in the oral cavity, followed by the nasal cavity (44%) and sinuses (8%)2. The most frequent sites in the oral cavity are the hard palate (more than 40%) and the gingiva2. Melanomas arise from the uninhibited proliferation of melanocytes found in the basal layer of the oral mucous membranes3. The clinical presentation of this neoplasm varies widely, from a typically pigmented macular or nodular lesion, to a non-pigmented neoplasm that may be solitary or multiple, primary or metastatic4. Less than 2% of all melanomas lack pigmentation, in the oral mucosa however, up to 75% of cases are amelanotic5, 6, 7.
In contrast to cutaneous melanomas, which may present with a horizontal or vertical growth pattern, oral melanomas usually present typically with vertical growth, thus spreading to contiguous sites early8. The prognosis for oral melanomas is poor, with an overall 5-year survival rate of 15%8.
In oral mucosa, melanocytes are located along the tips and peripheries of the rete pegs. No etiologic factors have been recognized for oral melanomas. Risk factors have also remained obscure. There appears to be no geographic variations and only minor ethnic and gender differences9. Some oral melanomas are believed to originate from junctional nevis, others are thought to arise from pre-existing Hutchinson’s malignant lentigo10. Some authors have suggested that oral habits and self medication may be of etiological significance in some Indian and African groups11. According to Tanaka et al12, the biological behavior of melanoma may be related to the expression of the proteins Rb, pRb2/ p130, p53 and p16, which may be helpful in predicting the manifestation of this neoplasm, including the melanin content.
Oral melanoma is rare but it is relatively frequent in countries like Japan, Uganda, and India13. Oral melanoma is a lesion of adulthood, rarely identified under the age of 20 years. In a study, the highest incidence of malignant melanoma was reported in the fifth to eight decades of life14. Hicks and Flaitz8 in a review of oral malignant melanoma showed a male predilection and an age range of 22 to 83 years, with a mean age of 56 years. There is a higher incidence of melanoma of the oral mucosa among Japanese than Caucasians15. According to an African research, 1.7% of all melanomas in Sudan occurred in the oropharynx and 0.9% of the melanomas in Nigeria originated within the oral cavity11. In Australia where cutaneous melanomas are relatively common primary melanoma of the oral mucosa is rare 14.
The surface architecture of oral melanomas ranges from macular to ulcerated and nodular9. Indeed clinically, the tumors are classified into five types: I – pigmented nodular, II – non-pigmented nodular, III – pigmented macular, IV – pigmented mixed, and V – non-pigmented mixed type16. The lesion is said to be asymptomatic in the early stages but may become ulcerated and painful in advanced lesions17
The diagnosis of amelanotic melanoma is more difficult than that of pigmented lesions18. Histological description of a specimen by Notani et al19 showed that the neoplasm consisted of spindle-shaped cells with many mitotic figures and there was no cytoplasmic melanin pigmentation. These malignant cells possess considerable pleomorphism, with large, irregular hyperchromatic nuclei and prominent nucleoli8. Others have reported pleomorphic epithelioid cells with bizarre nuclei, large cherry-red nucleoli, occasional nuclear pseudo-inclusions and variable amounts of dusty cytoplasmic pigment20.
Lesions that are suspected to be melanomas should be assessed both histologically and by immunohistochemistry, which are helpful in the diagnosis of amelanotic melanoma and only slightly pigmented melanoma21, 22. The immunohistochemical techniques using S-100, HMB-45, Melan-A and MART-1 will help in establishing the correct diagnosis21.
Notani et al19 suggests a combination of radical surgery with ample margins and adjuvant chemotherapy as an appropriate management protocol for malignant melanoma. Many chemotherapy agents have been used for malignant melanomas but dacarbazine was reported to have the best response rate of about 20% as a single agent23. The addition of the immunomodulator, OK- 432, injected around the neoplasm has been advocated for treatment and prolonging survival periods in oral lesions24.
Radiotherapy has been considered to have only a palliative role and on its own was reported to be ineffective since the lesion is not very radiosensitive25. On the other hand, Tanaka et al.16 found radiotherapy to be more successful than surgery for oral melanoma. The treatment of amelanotic melanoma does not differ in anyway from the pigmented neoplasm.