Intrathyroid papillary carcinomas and microangioinvasive follicular carcinomas are very slow-growing tumours in patients under the age of forty. This applies also to metastases, which may not become clinically apparent until five to ten or more years after the initial thyroidectomy; such metastases tend to occur either in the lymph nodes (papillary carcinomas) or in bones (follicular carcinomas). After the age of forty, previously diagnosed and newly-diagnosed tumours show a tendency to grow and spread more rapidly, usually associated with less well-differentiated histopathology.
