Abstract
<title>Abstract</title> <p> <bold>Rationale:</bold> NUT carcinoma (NC) is a rare and highly aggressive malignancy defined by rearrangements of the NUTM1gene. Primary NC of the submandibular gland is exceptionally rare, with nonspecific imaging features that often lead to misdiagnosis as common salivary gland tumors and delayed treatment. <bold>Patient concerns:</bold> A 32-year-old man presented with a painless mass in the left submandibular region that rapidly enlarged from 2 cm to approximately 4 cm within one month, accompanied by the development of ipsilateral pharyngeal and periauricular pain. <bold>Diagnoses:</bold> Preoperative multimodal imaging—computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography/computed tomography (PET/CT)—revealed an ill-defined, invasive mass with heterogeneous enhancement and intense metabolic activity (SUVmax 18.4). The diagnosis was confirmed by histopathological examination and immunohistochemical analysis, which demonstrated diffuse nuclear positivity for NUT protein. <bold>Interventions:</bold> The patient underwent radical surgical resection (left neck dissection), followed by adjuvant chemotherapy and radiotherapy. <bold>Outcomes:</bold> No evidence of local recurrence or metastatic disease was observed on follow-up imaging at 9 months postoperatively. <bold>Lessons:</bold> This case underscores that although the imaging features of submandibular gland NC are not pathognomonic, the combination of a rapidly growing invasive mass, heterogeneous enhancement, and marked hypermetabolism should raise clinical suspicion. Prompt biopsy with NUT immunohistochemical testing is essential for definitive diagnosis and early intervention, which is critical given the tumor's highly aggressive nature. </p>