A 43-year-old patient complains about a neoplasm in the right submandibular region that appeared a month ago after angina. The patient underwent antiinflammatory therapy but it led to no reduction of the neoplasm. Objectively: body temperature is up to 37, 2°C. Palpation reveals a slightly painful, spherical, freely movable, well-defined neoplasm of dense and elastic consistency in the right submandibular region. The duct of submandibular salivary gland discharges transparent saliva. The sublingual plica is unchanged. What is the most likely diagnosis?