A 52-year-old man from Delhi presents with a 6-month history of a painless, slow-growing swelling in the right parotid region. On examination, the swelling is firm, fixed to the underlying tissues, and the overlying skin appears normal. There is no facial nerve involvement. Intraoral examination reveals no abnormality. Fine needle aspiration cytology (FNAC) shows spindle cells arranged in fascicles with occasional mitotic figures. What is the most likely diagnosis?