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case_images: (A) Fusion PET-CT of the hypermetabolic primary tumor involving the right maxillary sinus and right parapharyngeal region. (B) CT (bone window) showing sclerotic bone metastases at right T9 and right 9th rib. (C) Fusion PET-CT of hypermetabolic bone metastases at right T9 and right 9th rib. (D) Fusion PET-CT of the primary tumor showing significant shrinkage and metabolic response. (E) CT (bone window) of lesions at right T9 and right 9th rib with radiological improvement. (F) Fusion PET-CT of lesions at right T9 and right 9th rib with metabolic response. (G) Contrast CT (soft tissue window) showing sustained tumor response with only residual mucosal thickening at the posterior wall of right maxillary sinus. (H) CT (bone window) of lesions at right T9 and right 9th rib with further radiological improvement.
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case_images: Due to the occurrence of grade 2 immunotherapy related hepatitis, the patient opted not to resume further immunotherapy PET-CT scan 2 months after pembrolizumab administration showed significant shrinkage of the maxilla mass and both the primary and metastatic lesions became isometabolic ( Figures 1D-F ). November 2023 showed responding disease with non-enhancing soft tissue thickening at the right maxillary sinus wall and continuous radiological improvement in the bone metastases ( Figures 1G, H ). Nasal endoscopy in November 2023 showed no definite exophytic lesion in the maxillary sinuses.
case_images: (A) Photomicrographs of hematoxylin-and-eosin (H&E)-stained sections (x100) from the tumor biopsy specimen showing sheets of malignant cells with high N/C ratio, mitotic activity and areas of abrupt keratinization consistent with poorly differentiated carcinoma. (B) Photomicrographs showing diffuse positivity of tumor cells with NUT immunostain (x200).
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case_images: Immunohistochemical staining of the malignant cells were diffusely positive for p40 and NUT immunostains ( Figure 2 ).
case_images: Treatment course of our patient.
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case_images: A summary of our patient's treatment course is provided in  Figure 3 .