A 45-year-old previously healthy man comes to the office for evaluation of a neck lump that has progressively enlarged over a month. He has no fever, neck pain, or hoarseness. On examination, there is a nontender, firm nodule in the upper portion of the left thyroid lobe. Laboratory studies reveal a normal serum TSH and elevated serum calcitonin. Neck ultrasonography shows a 2-cm hypoechoic thyroid nodule with microcalcifications. Fine-needle aspiration reveals spindle-shaped cells in an amorphous background. Which of the following gene alterations most likely contributed to this patient's condition?
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