Thyroid cancer is a malignant neoplasm that can originate from the follicular cells of the thyroid gland - papillary and follicular - or the C-cells (perifollicular) that produce calcitonin - medullary carcinoma. Thyroid cancer is the most common malignant tumour of the endocrine glands. In Poland, there are approximately 1,700 new cases per year. The highest incidence is between the ages of 40 and 50.