Follicular thyroid cancer

Follicular thyroid cancer is a form of thyroid cancer which occurs more commonly in women of over 50 years old. Thyroglobulin (Tg) can be used as a tumor marker for well-differentiated follicular thyroid cancer.

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Classification

It is not possible to distinguish between follicular adenoma and carcinoma on cytological grounds. If fine needle aspiration cytology (FNAC) suggests follicular neoplasm, thyroid lobectomy should be performed to establish the histopathological diagnosis.

• Follicular carcinoma tends to metastasize to lung and bone via the bloodstream.
• Papillary thyroid carcinoma commonly metastasizes to cervical lymph nodes.

HMGA2 has been proposed as a marker to identify malignant tumors.^[1]

Treatment

Treatment is usually surgical, followed by radioiodine.

Initial treatment

• Unilateral hemithyroidectomy (removal of one entire lobe of the thyroid) is uncommon due to the aggressive nature of this form of thyroid cancer.
• Total thyroidectomy is almost automatic with this diagnosis.^[2] This is invariably followed by radioiodine treatment at levels from 50 to 200 millicuries following two weeks of a low iodine diet (LID). Occasionally treatment must be repeated if annual scans indicate remaining cancerous tissue. Some physicians favor administering the maximum safe dose (calculated based on a number of factors), while others favor administering smaller doses, which may still be effective in ablating all thyroid tissue. I-131 is used for ablation of the thyroid tissue.

Minimally invasive thyroidectomy has been used in recent years in cases where the nodules are small.^[3]

Finding disease recurrence

Some studies have shown that thyroglobulin (Tg) testing combined with neck ultrasound is more productive in finding disease recurrence than full- or whole-body scans (WBS) using radioactive iodine. However, current protocol (in the USA) suggests a small number of clean annual WBS are required before relying on Tg testing plus neck ultrasound. When needed, whole body scans consist of withdrawal from thyroxine medication and/or injection of recombinant human Thyroid stimulating hormone (TSH). In both cases, a low iodine diet regimen must also be followed to optimize the takeup of the radioactive iodine dose. Low dose radioiodine of a few millicuries is administered. Full body nuclear medicine scan follows using a gamma camera. Scan doses of radioactive iodine may be I¹³¹ or I¹²³.

Recombinant human TSH, commercial name Thyrogen, is produced in cell culture from genetically engineered hamster cells.

Hurthle cell variant

Hurthle cell thyroid cancer is often considered a variant of follicular cell carcinoma.^[4] Hurthle cell forms are more likely than follicular carcinomas to be bilateral and multifocal and to metastasize to lymph nodes. Like follicular carcinoma, unilateral hemithyroidectomy is performed for non-invasive disease, and total thyroidectomy for invasive disease

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