Follicular cancer is an encapsulated lesion and comprises about 15 to 20% of all thyroid cancers. There is capsular invasion and angioinvasion. This cancer usually does not metastasize to regional or distant lymph nodes. Instead, haematogenous spread to distant sites such as bone, lung and liver occurs quite early.
There in fact two varieties of follicular cancer, one is encapsulated, well differentiated and of low grade malignancy. The other variety shows vascular invasion quite early and the primary tumor is the most aggressive of all well differentiated cancer.
This carcinoma tends to occur in older age group, with a pick incidence inthe fifth decade. It is three times more common in females than in males. Patients may present with a long history of goitre. Sudden recent change in the form of increase in size or diffuse swelling into a firm nodule is observed. Very often an asymptomatic, slowly enlarging thyroid nodule is the presenting feature. Pain and invasion to adjacent structures are late symptoms. Distant metastases are frequent, of which bony, pulmonary and liver metastases are the dominant ones. The bony metastases are usually osteolytic.
Encapsulated and low grade follicular cancer, which shows a low incidence of distant metastasis later on, is often treated with thyroid lobectomy. Near total thyroidectomy is done to facilitate later treatment with radioiodine if metastases occur.
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