When intact mucosa hides a malignancy: solid-type primary intraosseous carcinoma (PIOC, NOS) of the mandible: a case report and literature review

Abstract

Primary intraosseous carcinoma, not otherwise specified (PIOC, NOS) is a rare odontogenic carcinoma that arises within the jawbone from odontogenic epithelial remnants, with no initial connection to the oral mucosa. Its non-specific clinical and radiographic features overlap with benign odontogenic and inflammatory lesions, so diagnosis is often delayed and rests on histopathology. The 2017 and 2022 World Health Organization (WHO) classifications recognize PIOC, NOS without formal subtypes; earlier schemes described a solid ( de novo ) type arising without a cystic or tumorous precursor. A 53-year-old man with no tobacco or alcohol history presented with painful right mandibular and cheek swelling, purulent discharge through a cutaneous fistula and mobile right mandibular molars, persisting despite management as an odontogenic abscess. The oral mucosa was intact and there was no sensory disturbance. Cone-beam computed tomography showed a destructive radiolucent lesion from the right mandibular first molar to an impacted third molar, with buccolingual expansion, cortical thinning and probable lingual perforation. After extraction of the molars, incisional biopsy showed invasive well-differentiated keratinizing squamous cell carcinoma with keratin pearls and bone trabeculae encased by tumor nests, without a cystic or odontogenic tumor component. Staging CT identified no suspicious primary tumor within the imaged regions. The diagnosis was PIOC, NOS under WHO 2022; the tumor was well differentiated (Grade I) and corresponded to the historically described solid ( de novo ) type. Segmental mandibulectomy with right neck dissection revealed a 7-cm tumor with perineural and lymphovascular invasion and four positive level I lymph nodes; margins were clear. Postoperative radiotherapy (40 Gy in 20 fractions) with concurrent cisplatin followed. In August 2026, CT showed an operative-bed mass suspicious for locoregional recurrence, and paclitaxel–carboplatin chemotherapy began in September 2026. Solid-type PIOC, NOS can mimic benign odontogenic and inflammatory lesions beneath an intact mucosa. A destructive jaw lesion that fails to respond to treatment for infection should be biopsied without delay. Keratin pearls, infiltrative epithelial nests and bone invasion without mucosal continuity are decisive for diagnosis, and the nodal metastasis and suspected recurrence in this case underline the need for continued oncologic surveillance.