This is a unique case report of a 67-year-old female diagnosed with multiple myeloma and extensive use of intravenous bisphosphonate, whose clinical and radiographic presentation of an oral lesion made it challenging to confirm its definitive diagnosis. This patient was referred to the dental service for a suspected medication-related osteonecrosis of the jaw (MRONJ). Clinically, the lesion was located underneath a fixed partial denture in the left posterior mandible. There was a purulent swelling on the lingual side of the fixed partial denture, and a hyperplastic exophytic lesion on the buccal side of the bridge. Panoramic radiograph showed a well circumscribed radiolucent lesion in the left mandible. A biopsy of the gingival lesion on the buccal aspect was inconclusive. As the positron emission tomography scan showed lytic lesions, oral manifestation of multiple myeloma could not be ruled out. A computed tomography-guided biopsy of the left mandible showed plasma cell neoplasm in the histological analysis. Upon confirmed diagnosis, the patient was treated with 20Gy to the left mandible and subsequent debridement of the loose necrotic bone. Following treatment, this gingival lesion resolved completely, and the tumour has remained stable till date.