Follicular thyroid cancer surgery
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ammu Susheela, M.D. [2]
Overview
Surgery
This 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.
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, while papillary thyroid carcinoma commonly metastasizes to cervical lymph nodes.
Surgical 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. 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.
- 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.
Stage I and II Follicular Thyroid Cancer
Total Thyroidectomy
This procedure is advocated because of the high incidence of multicentric involvement of both lobes of the gland and the possibility of dedifferentiation of any residual tumor to the anaplastic cell type.\
The objective of surgery is to completely remove the primary tumor, while minimizing treatment-related morbidity, and to guide postoperative treatment with radioactive iodine (RAI). The goal of RAI is to ablate the remnant thyroid tissue to improve the specificity of thyroglobulin assays, which allows the detection of persistent disease by follow-up whole-body scanning. For patients undergoing RAI, removal of all normal thyroid tissue is an important surgical objective. Additionally, for accurate long-term surveillance, RAI whole-body scanning and measurement of serum thyroglobulin are affected by residual, normal thyroid tissue, and in these situations, near total or total thyroidectomy is required. This approach facilitates follow-up thyroid scanning.
I131: Studies have shown that a postoperative course of therapeutic (ablative) doses of I131 results in a decreased recurrence rate among high-risk patients with papillary and follicular carcinomas.[4] It may be given in addition to exogenous thyroid hormone but is not considered routine.[10] Patients presenting with papillary thyroid microcarcinomas (tumors <10 mm) have an excellent prognosis when treated surgically, and additional therapy with I131 would not be expected to improve the prognosis.
Lobectomy
Thyroid lobectomy alone may be sufficient treatment for small (<1 cm), low-risk, unifocal, intrathyroidal papillary carcinomas in the absence of prior head and neck irradiation or radiologically or clinically involved cervical nodal metastases. This procedure is associated with a lower incidence of complications, but approximately 5% to 10% of patients will have a recurrence in the thyroid following lobectomy.[12] Patients younger than 45 years will have the longest follow-up period and the greatest opportunity for recurrence. Follicular thyroid cancer commonly metastasizes to lungs and bone; with a remnant lobe in place, use of I131 as ablative therapy is compromised. Abnormal regional lymph nodes should be biopsied at the time of surgery. Recognized nodal involvement should be removed at initial surgery, but selective node removal can be performed, and radical neck dissection is usually not required. This results in a decreased recurrence rate but has not been shown to improve survival.
Following the surgical procedure, patients should receive postoperative treatment with exogenous thyroid hormone in doses sufficient to suppress thyroid-stimulating hormone (TSH); studies have shown a decreased incidence of recurrence when TSH is suppressed.
Stage III Follicular Thyroid Cancer
Standard treatment options:
Total thyroidectomy plus removal of involved lymph nodes or other sites of extrathyroid disease. I131 ablation following total thyroidectomy if the tumor demonstrates uptake of this isotope. External-beam radiation therapy if I131 uptake is minimal
Stage IV Follicular Thyroid Cancer
The most common sites of metastases are lymph nodes, lung, and bone. Treatment of lymph node metastases alone is often curative. Treatment of distant metastases is usually not curative but may produce significant palliation.
Standard treatment options for iodine-sensitive thyroid cancer:
I131: Metastases that demonstrate uptake of this isotope may be ablated by therapeutic doses of I131.
Standard treatment options for iodine-resistant thyroid cancer:
Thyroid-stimulating hormone suppression with thyroxine is effective in many lesions not sensitive to I131.