Can cystic thyroid nodule be cancerous?

Unlikely but ask doc: Most of the the thyroid nodules are benign, cystic nodules are even more benign, but sometimes a small focus of cancer could be inside the cyst, to be sure most of the time after fine needle aspiration (fna) will be done by your doctor send for biopsy ( cytology ) to be sure it is benign..

Unlikely: Completely cystic thyroid nodules are unlikely to be cancerous. They are more likely to expand and contract causing you to see them more but if they are completely cystic, no cancer.

Pure cyst?: A cyst of thyroid rarely carries a cancer. A complex nodule (greater than 50% fluid) carries a small risk cancer <3%.