A 47-year-old patient complains of a burning sensation and pain in the mouth. Objectively: on the mucous membrane of cheeks along the line of teeth contact and in the corners of mouth there are multiple polygonal bright red erosions 1,0-1,5 cm in diameter located on the hyperkeratinized plaque and opaque whitish mucosa. Cytological analysis revealed keratinizing epithelial cells. What is the most likely diagnosis?