How is anaplastic thyroid cancer ruled out? in particular distinguished from suspected papillary carcinoma? is it possible confusion between the two?

It is a lethal tumor: Papillary carcinoma of the thyroid presents as a solitary lesion that is cold on scan. During work up the lesion usually remains stable and rarely unless watched for a long time, free of nodal disease. Anaplastic carcinoma is virulent and if watched or even set up for biopsy rapidly invades the strap muscles of the neck and then quickly spreads into the neck to become unresectable.

Biopsy,,: Fine needle aspiration biopsy is what's done in order to determine whether or not anaplastic thyroid cancer is present. This has sheets of uniform looking cells with no differentiation while papillary thyroid cancer has distinct appearing nuclei called "orphan annie nuclei" from their similar appearance. Thyroglobulin is a good tumor marker for papillary thyroid cancer which has a good prognosis.

By tissue biopsy: Anaplastic thyroid ca (poorly differentiated) usually presents with a rapid enlarging neck mass. Papillary thyroid ca (well differentiated) usually presents with single or multiple thyroid nodules. Through tissue biopsy such as fine needle aspiration, pathologist should be able to distinguish between anaplastic and papillary thyroid ca relatively easily through morphology and molecular staining.

Anaplastic thyroid: Anaplastic thyroid cancer is suspected because of a rapidly growing thyroid mass. Usually patients present and it is obvious. You start with an fna but may need to do an open biopsy as part of a planned thyroid surgery and get a frozen section result or stop and defer to permanent pathology. The primary differential of this us lymphoma of the thyroid.