There are 2 main cell types within the thyroid gland, the follicular cell and C cells. Thyroid cancer exists on a spectrum of well differentiated to poorly differentiated and finally undifferentiated thyroid cancer. Differentiation refers to the degree with which the thyroid malignancy represents normal thyroid tissue. Generally the less differentiated the thyroid cancer is, the more aggressive its behaviour. The vast majority of thyroid cancers are differentiated thyroid cancers that arise from follicular thyroid cells and have an excellent prognosis.

Differentiated thyroid cancer:

Follicular cell derived

– Papillary thyroid carcinoma – very common and represents approximately 70-80% of thyroid cancer. Has an excellent prognosis

– Follicular thyroid carcinoma – the next most common type and makes up about 10-20% of thyroid cancers.

– Oncocytic cell carcinoma (previously Hurthle cell carcinoma) makes up <5% of thyroid cancers and usually seen in older patients

C cell origin

– Medullary thyroid carcinoma – makes up <5% of thyroid cancer. It is a neuroendocrine tumour and patients will require blood, urine and imaging to ensure they do not have other neuroendocrine tumours prior to surgery. About 25% of cases are inherited and 75% of cases are sporadic

Poorly differentiated thyroid cancers:

The cells in poorly differentiated thyroid cancers look a lot less like normal thyroid follicular cells and these types of tumors tend to grow more rapidly with a more aggressive pattern of behaviour. Examples of poorly differentiated thyroid cancers include solid, trabecular and insular variant thyroid cancer

Anaplastic thyroid cancer:

Is a highly aggressive rare form of thyroid cancer generally seen in older patients. It may arise from a pre-existing differentiated thyroid cancer that the patient was unaware of. It often has a rapid growth pattern and requires management in a multi-disciplinary high volume Head and Neck Endocrine unit with access to immunotherapy.