FMTC is a rare inherited form of cancer of the butterfly-shaped thyroid gland in the neck. The growth in the thyroid gland is always cancerous (medullary thyroid cancer or MTC). MTC may also occur alone and independently of FMTC/MEN2.

Blood tests for hormone levels as well as scans of the neck are all used to check for growths. If a growth is found an operation is needed to remove the whole of the affected gland. This is sometimes necessary in early childhood.