A 67-year-old patient complains about frequently recurring erosion in the area of vermilion border of his lower lip. The erosion is oval, 0,8х1,3 cm large, covered with thin crusts. After their removal some petechial hemorrhages on glossy surface can be seen. There are also some atrophied areas of the vermilion border. Infiltration is absent. Submandibular lymph nodes are not enlarged. What is your presumptive diagnosis?