Thyroid cancer surgery

Classification
Thyroid cancers can be classified according to their pathological characteristics. The following variants can be distinguished (distribution over various subtypes may show regional variation):
 * Papillary thyroid cancer (75%, incl. mixed papillary/follicular)
 * Follicular thyroid cancer (16%)
 * Medullary thyroid cancer (5-7%)
 * Anaplastic thyroid cancer (3%)
 * Lymphoma (1%)
 * Squamous cell carcinoma, sarcoma (0.5 - 2%)

Papillary thyroid cancer
This is the most common type of thyroid cancer. It occurs more frequently in women and presents in the 30-40 year age group. It is also the predominant cancer type in children with thyroid cancer, and in patients with thyroid cancer who have had previous radiation to the head and neck (in this group, the cancer tends to be multifocal with early lymphatic spread, and portends a relatively poor prognosis). Thyroglobulin can be used as a tumor marker for well-differentiated papillary thyroid cancer.

Surgical treatment

 * Minimal disease (diameter up to 1.0 centimeters) - hemithyroidectomy (or unilateral lobectomy) and isthmectomy may be sufficient. There is some discussion whether this is still preferable over total thyroidectomy for this group of patients.
 * Gross disease (diameter over 1.0 centimeters) - total thyroidectomy, and central compartment lymph node removal is the therapy of choice. Additional lateral neck nodes can be removed at the same time if an ultrasound guided FNA and thyrobulin TG cancer washing was positive on the pre-operative neck node ultrasound evaluation.

Arguments for total thyroidectomy are: Thyroid total body scans are less reliable at finding recurrence than TG and ultrasound.
 * Reduced risk of recurrence, if central compartment nodes are removed at the original surgery.
 * Papillary carcinoma is a multifocal disease (hemithyroidectomy may leave disease in the other lobe)
 * Ease of monitoring with thyroglobulin (sensitivity for picking up recurrence is increased in presence of total thyroidectomy, and ablation of remnant normal thyroid by low dose radioiodine 131 after following a low iodine diet (LID).
 * Ease of detection of metastatic disease by thyroid and neck node ultrasound.

Follicular thyroid cancer
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.