Familial Medullary Thyroid Carcinoma

A 42-year-old woman is referred after her brother was diagnosed with medullary thyroid carcinoma at age 38. She is asymptomatic but reports two paternal uncles who died of thyroid cancer in their 40s. There is NO family history of pheochromocytoma, hypertensive crises, or kidney stones. Thyroid ultrasound shows two small hypoechoic nodules with microcalcifications. Serum calcitonin is mildly elevated at 85 pg/mL (normal <10), CEA is normal, and plasma free metanephrines are normal on two occasions. Genetic testing reveals the mutation shown at **B** in the diagram. Based on this genetic finding and clinical presentation, what is the MOST appropriate next step in management?