A 65-year-old patient complains about pain during eating, reduced tongue mobility, an ulcer in the posterior part of mouth floor on the left, weight loss. Objectively: the patient uses a partial removable denture for the lower jaw. In the area of the left mylohyoid duct there is an ulcer in form of a cleft up to 1,6 cm long with everted edges, covered with grey-yellowish deposit, closely adhering to an infiltrate that can be detected during bimanual palpation. In the left submandibular and superolateral areas of neck several enlarged nonmobile lymph nodes can be palpated. What is the most probable diagnosis?