Year : 2010 | Volume
: 21 | Issue : 2 | Page : 302--305
Malignant melanoma of the mandibular gingiva: A rare occurrence
BVR Reddy, GR Sridhar, CH Anuradha, P Chandrasekhar, KP Lingamaneni
Department of Oral Pathology, Sibar Institute of Dental Sciences, Takkellapadu, Guntur, Andhra Pradesh, India
Department of Oral Pathology, Sibar Institute of Dental Sciences, Takkellapadu, Guntur, Andhra Pradesh
Primary mucosal malignant melanoma of the oral cavity is a rare tumor. It accounts for only 0.2-8% of all malignant melanomas. This malignancy commonly affects male subjects and is more frequently seen on the hard palate and maxillary gingiva. The peak age for diagnosis of oral melanoma is between 55 and 65 years. A biopsy is required to establish a diagnosis. Ablative surgery with tumor-free margins remains the treatment of choice. It has a much poorer prognosis than its counterpart on the skin. Here, we present a case of malignant melanoma of the mandibular lingual gingiva in a 55-year-old male patient. Immunohistochemistry and special stains were conducted for confirmatory diagnosis.
|How to cite this article:|
Reddy B, Sridhar G R, Anuradha C H, Chandrasekhar P, Lingamaneni K P. Malignant melanoma of the mandibular gingiva: A rare occurrence.Indian J Dent Res 2010;21:302-305
|How to cite this URL:|
Reddy B, Sridhar G R, Anuradha C H, Chandrasekhar P, Lingamaneni K P. Malignant melanoma of the mandibular gingiva: A rare occurrence. Indian J Dent Res [serial online] 2010 [cited 2021 Feb 27 ];21:302-305
Available from: https://www.ijdr.in/text.asp?2010/21/2/302/66644
Melanoma is a malignant neoplasm comprising of melanocytes, which are derived from the neural crest cells that constitute the melanin pigment of the basal layer of the epithelium. Although most melanomas arise from the skin, they may also arise from the mucosal surface or at other sites wherein neural crest cells migrate. 
Malignant melanoma of the oral cavity accounts for only 0.2-8% of all melanomas, and it has a much poorer prognosis than its counterpart on the skin. 
Oral melanoma occurs more commonly in the Japanese than in other groups. Male predilection exists, with a male to female ratio of almost 2:1. It is largely a disease of those older than 40 years, and it is rare in patients younger than 20 years.  It often occurs in the hard palate and the maxillary gingiva  . Its occurrence on the mandibular gingiva is extremely rare. 
A 54-year-old male patient reported to the Department of Oral Pathology, Sibar Institute of Dental Sciences, Guntur, with a chief complaint of pigmented lesion in the mandibular gingiva since 18 months. Patient's medical history was noncontributory. Extraoral examination revealed enlargement of the left submandibular lymphnode, which was oval in shape, freely movable and nontender on palpation [Figure 1]. Intraoral examination showed an elevated pigmented lesion, measuring about 1.5 cm on the lingual aspect of the left mandibular molar region, extending from the first molar to the third molar [Figure 2]. The mucosa in other areas appeared to be normal. Computerized tomographic scan (soft tissue window) showed involvement of the left submandibular lymph node [Figure 3]. Histopathological studies revealed numerous atypical melanocytes within the epithelium and also invasion into the connective tissue. These cells are epitheloid to spindle in shape, with vesicular, hyperchromatic nuclei and prominent nucleoli. Few mitotic figures are also seen. These cells are distributed into sheets and groups in the junctional location [Figure 4].
Lesional areas showed a dark black color for Masson's Fontana silver stain [Figure 5] and also positivity for the Melanin Bleach technique [Figure 6]. Immunohistochemical studies showed positivity for HMB 45 marker [Figure 7].
Based on the histopathological features and results of special stains, bleaching technique and immunohistochemistry, a confirmatory diagnosis of malignant melanoma was given.
The lesion was treated by surgical excision with the removal of the affected submandibular lymph node. The patient was referred to the Government General Hospital, Guntur, for further treatment.
Oral malignant melanoma (OMM) is a rare aggressive neoplasm comprising of melanocytes.  In the oral mucosa, melanocytes are located along the tips and peripheries of the rete pegs. The ratio of melanocytes to keratinocytes in the gingiva is 1:15. Melanocytes differ from nevus cells and melanoma cells in showing features of pleomorphism, hyperchromatism, prominent nucleoli and mitotic activity. 
The exact incidence rate of oral melanoma is not available. However, they are rare and estimated to represent 1-2% of all oral malignancies, with OMM accounting for 0.2-8% of all melanomas.  It is a rare aggressive neoplasm usually found on the hard palate and the gingiva.  Malignant melanoma of the mandibular gingiva is extremely rare. 
It generally occurs in adults between 55 and 65 years of age.  The tumor exhibits a slight male predilection. In this case also, the age and gender of the patient is in accordance with the above-mentioned findings.
According to Tanaka et al., oral melanomas could be classified into five types based on their clinical appearance: pigmented nodular, nonpigmented nodular, pigmented macular, pigmented mixed and nonpigmented mixed. The clinical coloration has a wide range, which can appear as black, grey, purple and even reddish. The tumors are asymmetric, irregular in outline and occasionally multiple.  Pain, ulceration and bleeding are rare in oral melanoma until late in the disease. 
Most malignant melanomas arise de novo; some may arise from pre-existing nevi, especially atypical (dysplastic) nevi, and congenital hairy nevi.  Many genes are implicated in the development of melanoma, including CDKN2A (p16), CDK4 (chromosome 12q15), RB1, CDKN2A (p19) and PTEN/MMAC1. ,
In contrast to cutaneous melanomas, which are etiologically linked to sun exposure, risk factors for mucosal melanomas are unknown. Currently, most oral melanomas are thought to arise de novo. 
Microscopically, melanomas in situ show an increase in atypical melanocytes. These atypical melanocytes have angular and hyperchromatic nuclei. Mitoses tend to be sparse. The melanocytes may form aggregates or may be irregularly distributed in a junctional location. The melanocytes present in invasive melanomas show a variety of cell types, including epitheloid, spindle and plasmacytoid. They typically have large, vesicular nuclei with prominent nucleoli. Mitoses may be present, but usually not in large numbers. They are usually aggregated into sheets or alveolar groups.  In this case also, the histopathological features coincide with the above-mentioned features.
Microstaging of primary mucosal melanoma are as follows: 
Level I: Pure in situ melanoma without evidence of invasion or in situ melanoma with microinvasion.
Level II: Invasion up to the lamina propria
Level III: Deep tissue invasion into the skeletal muscle, bone or cartilage
The present case fits into Level II, with invasion up to the lamina propria only.
About 10% of the cases are amelonotic. More than 95% of the lesions are anti S-100 antigen-positive, and more specific markers include HMB45, Melan-A and anti-tyrosinase.  Special stains like Masson's Fontana and melanin bleach are also helpful in the diagnosis of malignant melanoma.  In this case, Masson's Fontana, melanin bleach and HMB45 also showed positivity.
Differential diagnosis for OMM includes oral melanotic macule, smoking-associated melanosis, medication-induced melanosis, melanoplakia, pituitary-based Cushing's syndrome, postinflammatory pigmentation, melanoacanthoma, melanocytic nevi of the oral mucosa, blue nevi, spitz nevi, Addison's disease, Peutz-Jeghers syndrome, amalgam tattoo, Kaposis's sarcoma, physiologic pigmentation and many other conditions sharing macroscopic characteristics with OMM. This neoplasm should also be differentiated histopathologically from other malignant entities, such as poorly differentiated carcinoma and large cell anaplastic lymphoma. 
Surgery is the mainstay of treatment, but can be difficult due to anatomic restraints. Although melanoma is classically not radiosensitive, occasional patients have shown a good response to radiation therapy, especially in early or in situ melanomas. Immunotherapy has been successfully used but chemotherapy has demonstrated a relatively low response rate. Dacarbazine-DTIC, INF-gamma and INF-alpha-2b have been described as chemotheraupetical and immunotherapeutical treatments associated with Bacillus-Calmette-Guerin vaccine and recombinant interleukin-2 (rIL) in different combinations. 
Most oral melanomas are large at presentation and have a poorer prognosis than cutaneous melanoma. There are several criteria that may be used in evaluating the prognosis of malignant melanoma. Prasad et al. in 2002 revealed that the presence of vascular invasion was an important adverse prognostic finding for melanomas, as once the tumor gained access to lymphatic and blood circulation, its spread to distant sites is greatly facilitated. Following this line of analysis, long-distance metastasis remains as the most impacting prognosis factor for these tumors.  The Breslow and Clark grading systems have not been validated as prognostic predictors in oral melanomas, probably owing to the rarity of this lesion.  According to Pilskin, the 5-year survival rate for all oral melanomas is approximately 7%. 
Primary oral mucosal melanomas are exceedingly rare and biologically aggressive malignancies. OMMs clinically mimic many other pigmented lesions of the oral cavity. Dental and medical practitioners who treat oral lesions should include malignant melanoma in the differential diagnosis of pigmented lesions because early diagnosis and intervention results in better prognosis.
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