A 25-year-old man has a saucershaped ulcer 0,8 cm in diameter on the upper left surface of tongue. The ulcer's floor and edges are dense with smooth and glistening surface, painless on palpation. Microscopical examination of the ulcer floor revealed an infiltration consisting of lymphoid, plasmatic and epithelioid cells with a lot of vessels affected by endovasculitis. What is the most likely diagnosis?