To showcase a reported rare case of malignant melanoma in the posterior mandible, lacking a discernible primary source, to delve into its potential origins, and conduct a comparative analysis with documented occurrences of metastatic melanoma affecting the mandible.
Methodology: In May 2023, a 29-year-old female sought medical attention for a persistent, painful mass in the right back region of her mandible that had been troubling her for four months. Clinical examination revealed an ulcerated lesion in the retromolar region with pseudomembranous slough, accompanied by swelling in the vestibule on both the buccal and lingual sides. Palpation confirmed the presence of a localized, bony-hard swelling, which was tender on palpation. An OPG and CBCT were conducted, revealing a multilocular radiolucency extending from the right mandibular canine to the second molar, situated 5mm above the lower border of the mandible.
An incisional biopsy initially suggested a potential diagnoses of mucoepidermoid carcinoma, sarcomoid lesion, or myoepithelial carcinoma. FNAC results indicated malignancy, with possibilities including poorly differentiated carcinoma, malignant melanoma, or anaplastic lymphoma. Enucleation and curettage were performed, followed by IHC analysis, which indicated focal positivity for CK8/18, suggesting a poorly differentiated malignant tumour. Further investigations revealed a large tumour in the left mandibular ramus. The patient subsequently underwent wide local excision and reconstruction using Recon plate, radicle neck dissection, and reconstruction using a submammary PMMC flap. Pathological analysis revealed nested malignant cells with numerous mitoses, along with positivity for melanocytic markers such as S100, CD56, HMB45, and melan-A. Despite the primary tumour's elusive source, the patient, shows no clinical or radiological evidence of disease more than six months post-initial presentation, highlighting a remarkable and encouraging outcome.
Results: The patient is undergoing monthly follow-up sessions and receiving radiotherapy. Although it's early to assess survival rates, there is currently no clinical or radiological evidence of disease since the surgery two months ago.
Discussion: Metastatic tumours to the oral cavity are rare (1-3% of all oral malignancies), with the jawbones, particularly the mandible, being more commonly affected. Despite advances in systemic therapy, treating advanced melanomas remains challenging. Spontaneous regression is uncommon, with immunological factors likely playing a key role, though the exact mechanism remains unclear. Clausen and Poulsen (1963) outlined criteria for mandibular metastatic tumours, where positive S-100 immunohistochemical staining and negative HMB-45 are indicative. Typically, melanoma metastasizes to regional lymph nodes before reaching secondary sites.
Conclusion: This complex case highlights diagnostic challenges in rare malignancies, but through a comprehensive approach involving clinical, radiological, and pathological assessments, successful treatment and a promising outcome were achieved, underscoring the importance of early intervention and multidisciplinary care.
Keywords: malignant melanoma, S100, CD56, HMB45, melan-A
