Rising calcitonin after thyroidectomy

52-year-old man who had a total thyroidectomy with central and right lateral neck dissection 3 years ago for medullary thyroid carcinoma (pT2 N1b); germline RET testing was negative. Calcitonin was 250 pg/mL 12 months ago, 560 pg/mL 6 months ago and is 1300 pg/mL now (doubling time about 5 months); CEA has risen from 18 to 52 µg/L. Neck ultrasound shows a 9 mm suspicious right level IV node.