A Rare Continuum From Oral Submucous Fibrosis to Spindle Cell Squamous Carcinoma: A Case Report.

Spindle cell squamous carcinoma (SpCC) is a rare, aggressive sarcomatoid variant of squamous cell carcinoma (SCC) characterized by biphasic epithelial-mesenchymal morphology. Oral submucous fibrosis (OSMF), a potentially malignant disorder prevalent in South-Asia typically transforms into conventional SCC, while direct transformation into SpCC is exceedingly uncommon. We report the case of a 49-year-old male previously treated for OSMF who, four years later, developed a fissural defect in the right buccal vestibule without an exophytic mass. He returned one week later with numbness of the right lower lip and chin. An incisional biopsy demonstrated well-differentiated SCC, while definitive resection revealed predominant spindle-cell morphology consistent with SpCC (pT4aN2a). The histologic continuity between epithelial and spindle components suggests early epithelial dedifferentiation within the OSMF microenvironment, likely mediated by TGF-β-driven epithelial-mesenchymal transition. This case underscores the malignant potential of OSMF and highlights the importance of recognizing such atypical malignant transformations, which are vital for timely diagnosis and intervention.