A 52 year old man, presents to the surgery outpatient clinic complaining of left neck rapidly growing swelling. On examination it seems to involve the left thyroid lobe. Radiography shows left thyroid mass invading the sternomastoid muscle. True cut biopsy shows malignant tumor by H&E staining, amyloid material by congo red stain and +ve calcitonin immunohistochemical stain.

What is the most likely diagnosis of this case?