Background: Granular cell tumors (GCTs) are uncommon soft tissue neoplasms of Schwann cell origin, typically presenting as benign, slow-growing lesions. Malignant transformation is rare, occurring in only 1–2% of cases, and is associated with aggressive behavior and poor prognosis. Spinal involvement is exceedingly uncommon, with limited cases reported in the literature.

Case Presentation: We report a rare case of a 55-year-old Filipina with a history of controlled hypertension who presented with progressively worsening upper back pain and functional decline. Initial imaging demonstrated compression deformities at the T9–T10 levels, initially suggestive of tuberculous spondylitis. The patient underwent surgical excision and stabilization, with histopathology confirming a benign granular cell tumor of the T10 vertebra. Despite initial postoperative improvement, she developed recurrence characterized by an enlarging paravertebral mass, worsening ambulatory difficulty, and dyspnea. Repeat imaging revealed a large, lobulated mass with infiltration into adjacent structures. Eight months after the initial surgery, tumor debulking and posterior stabilization were performed. Histopathologic evaluation demonstrated malignant transformation of the previously benign lesion, with involvement of skeletal muscle and bone. The patient was subsequently diagnosed with Stage IV malignant granular cell tumor and managed with palliative therapy, including Pazopanib and supportive care.

Conclusion: This case represents a rare instance of malignant transformation of a spinal granular cell tumor, highlighting the aggressive potential of these lesions despite an initially benign diagnosis. Given the rarity of spinal GCTs and their potential for malignant progression, complete surgical excision with clear margins and vigilant long-term follow-up are essential. A multidisciplinary approach is crucial for optimizing outcomes and managing complications.