The thyroid nodule

A 42-year-old woman presents with a palpable mass on the left side of her neck. She has no neck pain and no symptoms of thyroid dysfunction. Physical examination reveals a solitary, mobile thyroid nodule, 2 cm by 3 cm, without lymphadenopathy. The patient has no family history of thyroid disease and no history of external irradiation. Which investigations should be performed? Assuming that the nodule is benign, which, if any, treatment should be recommended?