An Unusual and Rare Case of Primary Oral Malignant Melanoma Involving the Mandible in a Young Female | Insight Medical Publishing

Background: Primary oral malignant melanomas (POMM) are rare and have been estimated to represent 1.6% of all oral malignancies and 0.2-8% of all melanomas. Most cases of melanomas involve palate and maxillary gingiva (80%) and about 20% involve mandible. The purpose of this article is to report a very unusual and rare case of melanoma in a young female involving mandible causing extreme destruction of bone. Methods and Findings: A 23 year-old female presented with a painful swelling over right mandible since 3 months. The growth extended from right preauricular region to submandibular region, was nodular and bluish black in colour and bled on touching. It caused displacement of mandibular premolars and molars. A provisional diagnosis of malignant osteolytic tumor was made. The patient underwent right hemimandibulectomy. Intraoperatively, the tumor was seen involving the entire mandibular body. On gross examination, right hemimandibulectomy specimen was received in pieces measuring 12 × 9.5 × 5.2 cm containing seven teeth. The tumor had perforated the lingual cortical plate. Cut surface was friable and black in colour. Microscopy showed a biphasic high grade neoplasm comprising of round to spindled tumor cells exhibiting marked nuclear pleomorphism and brisk mitosis, laden with granular brownish pigment melanin. The findings were consistent with the diagnosis of pigmented malignant melanoma and confirmed on immunohistochemistry as the tumor expressed vimentin and HMB45 and was negative for CK, EMA and p40. Conclusion: Involvement of mandibular bone by melanoma is rare. However, when they involve the bone, they are indistinguishable from other lytic malignant tumors or osteomyelitis. The present case emphasizes the need to learn the unusual location, the possible presentation of oral melanoma and inclusion of this rare tumor in the differential diagnosis of lytic bone tumors.