A 53-year-old patient consulted a dentist about pain and an ulcer that turned up in the region of hard palate under his partial removable denture. He hasn't used the denture for three weeks, but the ulcer does not heal or reduce in size. Examination reveals a 2x1,5 cm large ulcer in the region of the alveolar process and hard palate at the level of the missing 14 tooth. The ulcer has everted rolled edges and necrotic floor, it is dense and painful. Gingival and palatal tissues around the ulcer are infiltrated. What is the most likely diagnosis?