First presentation of disseminated renal cell carcinoma in the buccal mucosa with synchronous skeletal metastases: a case report

Metastasis to the oral cavity is rare, accounting for approximately 1–3% of all oral malignancies, with renal cell carcinoma (RCC) being one of the recognized primary sources. Among oral sites, buccal mucosal involvement is exceedingly uncommon and may pose significant diagnostic challenges due to its clinical resemblance to benign reactive lesions. We report a case of a 75-year-old male presenting with an exophytic, erythematous, and highly vascular lesion of the buccal mucosa, clinically mimicking a pyogenic granuloma. Histopathological examination revealed clear cell morphology in a richly vascular stroma. Immunohistochemistry showed positivity for PanCK and PAX8, with negativity for CK7, SOX2, and p40, confirming metastatic clear cell RCC. Notably, this oral lesion represented the first clinical manifestation of an otherwise occult malignancy. Subsequent positron emission tomography–computed tomography (PET-CT) demonstrated FDG-avid lesions in the buccal mucosa along with synchronous skeletal metastases involving the humeral head, manubrium sterni, and scapula, indicating disseminated disease. Laboratory investigations revealed macrocytic anemia (Hb 8.0 g/dL), vitamin B12 deficiency, hypoalbuminemia, and low total protein, suggesting compromised systemic status. The patient received systemic therapy with nivolumab and cabozantinib, along with denosumab for skeletal metastases for 6 months, but subsequently declined further treatment. This case highlights the critical role of dental surgeons in diagnosis of oral metastatic tumours presenting as innocuous oral lesions. Differentiation from pyogenic granuloma is essential, particularly in elderly patients with atypical features such as rapid growth and excessive vascularity. In light of recent systematic reviews and limited reported cases, this case adds to the scarce literature on buccal mucosal metastasis of RCC and underscores the importance of a multidisciplinary diagnostic approach.