A 65-year-old woman was referred to our clinic with a tumor in the right lower gingiva. Her medical history included breast cancer without metastatic lesion, diabetes mellitus, hyperlipidemia, and hypertension. She had taken orally aspirin, amlodipine, pravastatin, and bepotastine for 2 years. She drank alcohol socially, but she had no history of tobacco smoking habit.

About 10 years prior to her attendance at our clinic, her mandibular right posterior teeth had been replaced with an implant-supported porcelain-fused-to-metal restoration (three endosseous hydroxyapatite-coated titanium implants) in a dental clinic. The postoperative clinical course was uneventful, and the implant-supported restoration had functioned well. The patient had discontinued her regular follow-up for the maintenance of oral hygiene several months after the completion of the restoration. After about 7 years, she noticed a swelling on the lingual side of the gingiva around the three implants, and she visited a dental clinic. Following conservative treatment with nonsurgical measures for around 2 years, under a diagnosis of peri-implantitis, flap surgery to her lesion was performed in the dental clinic. However, the lesion around the central of the three implants did not improve, and changes to its surface properties were observed, leading to the suspicion of transformation to neoplasia. She was then referred to our clinic 3 months after the flap surgery.

The upper part of the implant body was exposed on the implant corresponding to the first molar of the right side of the mandible; this was associated with painless, elastic soft, and relatively well circumscribed gingival swelling on the lingual site. No pus drainage from the gingival sulcus was observed (Fig. 1). Periodontal disease or peri-implant disease, including peri-implantitis and peri-implant mucositis, were not observed in other regions, including the contiguous implants to the relevant middle implant. Lymphadenopathy in the neck was not detected. A panoramic radiograph showed slight vertical bone resorption around the three implants in the right side of the mandible (Fig. 2). An incisional biopsy was conducted under the suspicion of neoplasia after considering not only the clinical findings, but also the clinical course. Pathological microscopic examination of the biopsy specimen revealed thickened squamous epithelia with slight nuclear atypism and disorders of the epithelial rete pegs accompanied by moderate grade inflammatory cell infiltration. Immunohistochemical findings showed positive staining for keratin 17 (k17) and a negative staining mosaic pattern for keratin 13 (k13). High p53, p63, and Ki-67 reactivity was also observed in the basal cell layer, but negative staining for p16 (Table 1). These findings indicated to OIN/CIS. Thus, a wide local excision with rim resection of the mandible, including the three implants, was performed under general anesthesia. The postoperative clinical course was uneventful but the patient experienced paresthesia of the lower lip and mental region of the affected side. The pathological diagnosis of the resected specimen confirmed the OIN/CIS found in the biopsy specimen (Figs. 3, 4 and 5). The surgical margin was involved with epithelial dysplasia but free of OIN/CIS. After 1 year of follow-up, there was no evidence of recurrence (Fig. 6).