Spindle cell squamous cell carcinoma (SpSCC) is a rare biphasic malignant neoplasm, uncommonly affecting the oral cavity. The SpSCC diagnosis is difficult, especially when it exhibits inconspicuous morphology, inadequate tissue sampling, or association with an exuberant inflammatory reaction. Post-radiotherapy recurrent SpSCC occurring at the same site of conventional SCC is a rare phenomenon. A 59-year-old man was complained of "painful injury on the tongue" with 20 days of duration. He reported smoking and alcohol consumption. Medical history revealed conventional SCC on the tongue treated with surgery and radiotherapy 10 years ago. Intraoral examination showed a polypoid lesion with ulcerated areas, measuring 3 cm in diameter, on the tongue and floor of the mouth, at the same site of previous conventional SCC. The microscopical analysis showed small foci of carcinomatous component admixed with an exuberant inflammatory reaction. Immunohistochemistry highlighted the sarcomatoid component. Both malignant components were positive for EMA, CD138, p40 (deltaNp63), p63, and p53. Moreover, CK AE1/AE3 evidenced the carcinomatous component, whereas vimentin stained the sarcomatoid component. The Ki-67 was >10%. The current case emphasizes the importance of immunohistochemistry in the differential diagnosis of SpSCC from mimics and documents a rare complication of Ionizing Radiation.