Dictionary

Many abbreviations and terms used when talking about thyroid cancer may be new to you.  This is a list of some commonly used phrases, terms and abbreviations with brief explanations to help you navigate more easily.  See Resources for more detailed information.

Common Abbreviations

TT – Total thyroidectomy
TSH – Thyroid Stimulating Hormone
TH – Thyroid Hormone/s
T4 – Thyroxine, primary thyroid hormone
T3 – Triiodothyronine, the biologically active hormone
Free T4 – Unbound (not bound to protein receptors) T4
Free T3 – Unbound T3 able to be utilized by cells
Reverse T3 – isomer of T3, inactive
LID – Low Iodine Diet
NED – No evidence of disease
NDT – Natural desiccated thyroid (DTE)
DTE – Dessicated thyroid extract (NDT)
RAI – Radioactive Iodine
Tg – Thyroglobulin
TgAb – Thyroglobulin antibodies
THR – Thyroid hormone replacement therapy (not to be confused with TRH)
TRH – Thyrotropin-releasing hormone
TI-RADS – Thyroid Imaging Reporting & Data System

Types of Thyroid Cancer

Whether or not a nodule or lymph node is determined to be cancer is based on initial biopsy and surgical pathology examination.

Papillary and follicular thyroid carcinomas are referred to as well-differentiated thyroid cancer and account for over 90% of all thyroid cancers. Variants include tall cell, insular, columnar, and Hurthle cell. 

Medullary thyroid carcinoma (MTC) accounts for 3-4% of all thyroid cancers. It is actually cancer of C cells inside the thyroid rather than cancer in the thyroid cells.

Anaplastic thyroid carcinoma is the least common and accounts for only 1–2% of all thyroid cancer. It is a very aggressive type of thyroid cancer.

RAI Resistant thyroid cancer or non-iodine avid is thyroid cancer which does not take up iodine so is resistant to RAI therapy.

Thyroid Cancer Staging is based on the results of the physical examination, biopsy, imaging tests and the pathologic findings of surgery itself. 

See https://www.thyroidcancer.com/thyroid-cancer/papillary/staging for additional information.

Treatment Options

The primary initial treatment for all types of thyroid cancer is surgery to remove the thyroid gland and related lymph nodes. 

Thyroidectomy is the removal of the entire thyroid gland. Also referred to as Total Thyroidectomy (TT). Adjacent or “sentinel” lymph nodes are also removed for pathology. A radical neck dissection includes removing suspicious lymph node chains.

Hemi–thyroidectomy or partial thyroidectomy is the removal of just one of the two thyroid lobes.

Active Surveillance or watchful waiting is an alternative to surgery for small and low risk carcinomas and following hemi-thyroidectomy.  It involves close monitoring by ultrasound over time. 

Radioactive Iodine (RAI) is a follow-up treatment to ablate (destroy) thyroid cells which were not removed during surgery or which are detected during later monitoring. Current trends are to using the lowest possible effective dose.

TSH Suppressionmaintaining a low TSH level following surgery is used to lessen the risk of recurrence. 100% surgical or RAI ablation isn’t always possible and high TSH may encourage remnant thyroid cells to grow.  See TSH Suppression.

Thyroid Hormone Replacement (THR)

When the thyroid is removed, the patient becomes dependent on thyroid hormone replacement therapy medication to maintain body functions. THR may also be needed following hemi-thyroidectomy.

Levothyroxine (T4) is a synthetic thyroid hormone, similar to the thyroxine normally produced by the thyroid. The “4” stands for four iodine atoms. T4 is a “prohormone” which needs to be converted to the metabolically active T3 form by the body. Also referred to as “LT4” or by the primary brand name Synthroid.

Liothyronine (T3) is a synthetic version of the active form of thyroid hormone, similar to the triiodothyronine produced by the thyroid or converted from T4 in the body. T3 contains three iodine atoms. Often referred to by the common brand name Cytomel. 

Combination Therapy is THR therapy which combines both T4 and T3 to more closely mimic normal thyroid function. Because T3 has a short half life, the dose is usually divided into two or three doses during the day. It may use synthetic or “natural” forms (DTE) of thyroid hormone.

Desiccated Thyroid Extract (DTE) is thyroid hormone extracted primarily from freeze dried porcine (pig) thyroids, also called Natural Desiccated Thyroid (NDT). It combines T4 and T3 in standardized amounts as a prescription medicine.

Several branded and generic options are available for prescriptions for each type of thyroid hormone and are formulated with different filler ingredients and in varying dosages.

Thyroid Replacement Hormones are measured in micrograms – mcg or μg.

  • Mcg (microgram/s): one thousandth of a milligram
  • Mg (milligram/s): one thousandth of a gram
  • Grain: an apothecary (medical) measurement equal to exactly 64.79891 milligrams — nominal 65 mg or rounded down to 60 mg. Often used for DTE dosages where 1 grain of DTE equals 65 or 60 mg depending on the brand. Each grain of DTE contains 38 mcg of T4 and 9 mcg of T3. 

Thyroid Blood Testing

High doses of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R) can interfere with thyroid tests. Biotin consumption should be stopped at least 72 hours before testing. Biotin may be present in many supplements and in sports and energy drinks and snacks.

Also see What Blood Tests Should I Request?

TRH (Thyrotropin-releasing hormone) The hypothalamus senses circulating levels of T4 and T3. then produces TRH to stimulate the anterior pituitary gland to release thyroid-stimulating hormone (TSH). TRH is rarely tested unless a pituitary problem is suspected. See the Quick Thyroid Tour.

TSH (Thyroid Stimulating Hormone) Thyroid-stimulating hormone (TSH) is produced in the pituitary gland, a small organ located below the brain, and stimulates a normal thyroid to release the hormones thyroxine (T4) and triiodothyronine (T3) into the blood. 
– As T4 and/or T3 levels rise, TSH levels should go down (negative feedback).
– Initial TSH suppression to 0.1– 0.5 mU/L is recommended. See TSH Suppression.

Total and Free T4, Total and Free T3 These tests measure the amount of total (protein bound) and free (biologically active) thyroid hormone circulating in your blood.  The normal thyroid produces about 80% T4 (thyroxine) and 20% T3 ( triiodothyronine). To become metabolically active, T4 needs to be “converted” to T3 in the body by the liver, kidneys and other tissue by removing an iodine atom.
– Free T4 – measures unbound circulating thyroxine (T4).
– Free T3 – measures unbound circulating triiodothyronine (T3), the biologically active hormone which is utilized at the cellular level for energy production.

Reverse triiodothyronine (reverse T3 or rT3) is an isomer of triiodothyronine (T3) with no demonstrated biological activity.  It may be a response to other illness or inflammation. (An isomer has the same molecular formula but the atoms are arranged differently.)

Thyroglobulin (Tg) is a glycoprotein produced by follicular thyroid cells. It is the primary marker used to monitor for recurrence of thyroid cancer. In healthy thyroid glands it acts as a substrate for the synthesis of thyroid hormone.

Thyroglobulin Antibodies (TgAb) or anti-thyroglobulin antibodies) can interfere with thyroglobulin testing. 
– When testing Tg, if TgAb is negative a sensitive Tg-IMA test is used. If TgAb is positive, then the less sensitive Tg-RIA assay or the more recent Tg-LC/MS-MS (Thyroglobulin by liquid chromatography/tandem mass spectrometry or “mass spec”) is used to avoid interference from antibodies. See Tg Antibodies Rising

Calcitonin is a hormone involved in the regulation of calcium levels secreted by parafollicular cells (also known as C cells) of the thyroid gland. It is measured diagnostically before surgery if medullary thyroid cancer is suspected and, along with CEA, used to monitor for persistent or recurrent disease.

Carcinoembryonic antigen (CEA) is a glycoprotein which can become elevated in several types of cancer. It is not used alone to diagnose or monitor cancer.

Parathyroid Hormone (PTH) regulates stable levels of calcium in the blood. It is part of a feedback loop that includes calcium, PTH, vitamin D, and, to some extent, phosphorus (phosphate) and magnesium. The parathyroid glands are four tiny glands located at the back of the thyroid and are sometimes damaged, temporarily “stunned” or may even be removed during thyroid surgery.

Additional Detailed Testing Information may be found at these sites:
https://en.wikipedia.org/wiki/Thyroid_hormones
https://www.labcorp.com/test-menu/search
https://labtestsonline.org/search?keywords=Thyroid

Imaging and Procedures

Thyroid Ultrasound uses high-frequency sound waves to produce images of structures within your body and is commonly used to evaluate lumps or nodules found during a routine physical or other imaging exam.
– The images are read by a radiologist or endocrinologist using a scoring system such as TI-RADS to determine if a nodule is suspicious for cancer.
– Lymph node mapping is a more extensive ultrasound which is used to evaluate all the cervical lymph nodes for pre-surgery planning and as a baseline for ongoing monitoring for recurrence.

FNA (Fine Needle Aspiration) is a biopsy procedure, usually done in the doctor’s office, to determine if a thyroid nodule or lymph node is benign or cancerous. A fine needle is inserted under ultrasound guidance to obtain cell samples.

Thyroglobulin washout or lymph node aspirate is used to detect thyroglobulin produced by thyroid cancer in a suspicious lymph node.

Biopsy is the sampling of a suspected nodule or tumor tissue to determine if cancer is present. The sample is examined by a pathologist to determine type and staging of cancer tumors.

Radioactive Iodine (I-131) is used to ablate (destroy) remnant thyroid cells following thyroidectomy.  The RAI collects mainly in thyroid cells, where the radiation can destroy any remaining thyroid cells (including cancer cells) that take up iodine, with little effect on the rest of your body.
– RAI requires a low iodine diet for two weeks before treatment and isolation following treatment for up to a week to protect others from radiation.
– Preparation includes stimulating any existing thyroid cells by either withholding thyroid hormone replacement or injecting the medication Thyrogen to encourage uptake of the RAI.

Whole Body Scan (WBS) uses a small amount of a radioiodine tracer (I-123) to check to see if cancer has spread to other areas of the body. It may also be used to help determine the dosage of I-131 needed for RAI ablation.  I-123 has a shorter half life — 13 hours — compared to I-131 which has a half life of 8 days. 
– Preparation for WBS is similar to preparation for RAI.

PET Scan (Positron Emission Tomography, FDG-PET, PET-CT)is an imaging technique used to detect cancer metastasis or reoccurrence. It uses FDG, a glucose analog combined with a positron-emitting radionuclide which is taken up by tissue with heightened metabolic activity. 
– The PET scan is overlaid onto a CT scan to provide precise anatomical markers.
– 18F–FDG is the most common tracer used, other tracers may be used for specific situations.

Additional Terms and Descriptions

Thyrogen (thyrotropin alfa) is an injectable medication used to help patients prepare for treatment with RAI. 
– For RAI and WBS you need a high level of thyroid stimulating hormone (TSH).To obtain a high level of TSH, your doctor may temporarily stop (withdraw) your thyroid hormone medication for four to six weeks which may cause you to be hypothyroid.
– Thyrogen injection can raise TSH without causing a lengthy period of being hypothyroid and is preferred by many physicians. 
See https://www.thyrogen.com/patients for more information.

Low Iodine Diet (LID) is used in preparation for WBS or RAI. Foods and beverages containing iodine are avoided for about two weeks before and a few days following treatment so that any thyroid cells have greater uptake of the radioactive iodine tracer.
– The diet is low iodine, not to be mistaken for low salt.
– See http://www.thyca.org/pap-fol/lowiodinediet/  

Tyrosine kinase inhibitors (TKI’s) are a class of drugs that inhibit tyrosine kinases — enzymes responsible for the activation of many proteins. Some TKIs  have been proven to be effective anti-tumor and anti-leukemic agents and are being used to treat advanced thyroid cancers. 
– Other targeted cancer therapies are being studied and introduced. See https://www.cancer.gov/about-cancer/treatment/types/targeted-therapies/targeted-therapies-fa

Genomic Sequencing is used to further classify thyroid nodules which are found to be “indeterminate” on biopsy.  There are currently two tests available — Affirma and ThyroSeq.
https://www.afirma.com/physicians/
https://thyroseq.com/home 

TI-RADS – Thyroid Imaging Reporting & Data System is a system to describe thyroid nodules on sonography and provide a standardized TI-RADS risk-stratification system to inform practitioners about which nodules warrant biopsy. 
https://www.acr.org/Clinical-Resources/Reporting-and-Data-Systems/TI-RADS 

— Updates will be added as they become available —