If an individual is suspected to have thyroid cancer due to the presence of signs and symptoms, some investigations are required to confirm the diagnosis of the disease.
They help in distinguishing between benign thyroid disease (a benign nodule, goiter, or Grave’s disease) and thyroid cancer. Further, these investigations can help in determining the stage of disease , which in turn helps in selecting an appropriate treatment.
Following are some commonly used diagnostic tools for thyroid cancer:
- Thyroid ultrasound: In this technique, a transducer is used which directs very high-frequency sound waves towards the tissue to be examined. The sound waves are reflected off the internal structures depending on their ability to reflect these waves. The reflected sound waves are collected by a special detector (fixed near the transducer) to produce a real-time image of the internal tissues on a computer screen.
This helps the doctor to examine the thyroid tissue for any abnormality. This test can distinguish between fluid-filled cysts (mostly benign) and solid tumor masses (mostly cancerous). The test can reveal certain features of the cancerous nodules like micro-calcifications, irregular borders, or abnormal vascular patterns. Nearby lymph nodes (both in the lateral and the central neck) can also be studied for any sign of cancer spread with the help of this test. This technique can sometimes be used to guide a biopsy needle to collect biopsy samples from the affected area. This test does not use any ionizing radiation and is considered as safe.
- Blood Tests: Blood tests are not used to diagnose thyroid cancer itself but these tests can reveal certain important information that can provide direction to the diagnostic workup of thyroid cancer. Following are commonly employed blood test for this purpose.
Thyroid Hormone Level: The level of thyroid hormones – thyroxine and tri-iodothyronine, may be utilized to assess the functioning of thyroid gland. The thyroid hormone level is usually normal in most thyroid cancers but may be elevated in case of hyperfunctioning thyroid cancer and may require further investigations.
Thyroid Stimulating Hormone (TSH) Level: The TSH is secreted by the anterior pituitary and its level in the blood is regulated through negative feedback mechanism by thyroid hormones. Thus, an elevated level of TSH indicates diminished thyroid functioning while a suppressed TSH level indicates hyperfunctioning thyroid (or thyroid nodule). The hyperfunctioning thyroid nodules are rarely cancerous and can be easily detected with the help of radioiodine scan. No further investigation is generally required unless a cold nodule (an area in the thyroid with lower radioactivity then surrounding) is present. Cold nodules can be cancerous and thus require further investigation.
Calcitonin Level: Calcitonin is a hormone secreted by C-cells of the thyroid gland. These cells give rise to MTC that is usually associated with elevated level of calcitonin. Thus, elevated calcitonin level may signal MTC and should be handled appropriately. Calcitonin level estimation may also be helpful in the assessment of the efficacy of the treatment/surgery for MTC (which generally cause calcitonin level to decrease) and the progression/recurrence of the disease in patients with MTC (indicated by increased calcitonin level after the decrease caused by the treatment).
Thyroglobulin Level: Thyroglobulin is a protein made by thyroid cells and its level in the blood usually remains normal in most thyroid cancers. However, level of thyroglobulin can be helpful in assessing the efficacy of the treatment/surgery (that should bring down the thyroglobulin level) and the progression/recurrence of the disease in patients with DTC (if thyroglobulin level increases, which was diminished after treatment).
Carcinoembryonic antigen (CEA): CEA is a protein (tumor marker) that is found to be elevated in many patients with thyroid cancer (especially MTC). Monitoring of CEA level can be helpful in assessing the efficacy of the treatment/surgery (that should bring down the elevated CEA level) and the progression/recurrence of the disease in MTC patients who had high CEA levels before treatment.
- Radioiodine (I-131) Scan: In this test, radioiodine (I-131) is first administered to a patient. Iodine is essential for making thyroid hormones by follicular cells of the thyroid gland. Thus, radioiodine is absorbed by the thyroid follicular cells including the thyroid cancer cells (papillary, follicular, or Hürthle cell). This absorption of radioiodine occurs under the influence of TSH, and thus, a higher TSH level is usually achieved by injecting thyrotropin (recombinant TSH) to the patient before radioiodine dosing.
The whole body is then scanned for the presence of radioiodine with the help of a radioactivity detector. Abnormal areas in thyroid gland with low radioactivity compared to the surrounding are known as ‘cold nodules’, while the areas with high radioactivity than surrounding are known as ‘hot nodules’. Cold nodules can be cancerous and require further investigation while hot nodules are usually benign.
This test is mostly utilized to assess the efficacy of a treatment/surgery and the spread/recurrence of the disease in patients with DTC. If cancer cells are detected on radioiodine scan after surgical removal of the thyroid gland, it indicates spread of disease and disease sensitive to radioiodine therapy.
- Thyroid Biopsy: This is a confirmatory test and considered as gold standard in establishing the diagnosis of thyroid cancer. Biopsy sample(s) is generally collected from the suspected areas or cold nodules observed during the thyroid ultrasound or radioiodine scan, respectively.
A fine needle aspiration (FNA) biopsy technique is generally utilized for the diagnosis of thyroid cancer. Sometimes, biopsy sample(s) from lymph nodes in the central or lateral neck region is also collected for examination.
The collected biopsy samples are examined under the microscope in a laboratory and can provide very useful information such as the type of thyroid cancer, the severity of cancerous changes involved (level of differentiation), and the presence of specific defective genes or proteins in the cancer cells.
- Imaging Tests: These tests are generally employed after the establishment of the pathological diagnosis. They help to detect the spread of disease to distant body parts and assess the stage of the disease so that an appropriate treatment option can be selected.
Alternatively, these tests are employed after treatment to evaluate the treatment efficacy and to detect disease response, progression, or recurrence.
Computed tomography (CT) scan: In this technique, detailed cross-sectional images of body organs are generated using x-rays, with or without a contrast medium. It can help diagnose the spread of disease to nearby/distant lymph nodes and other organs, and may also be used to guide a biopsy needle into the affected area.
Magnetic resonance imaging (MRI) scan: This technique provides detailed images of tissues inside the body using radio waves, strong magnetic field, and gadolinium contrast. It can accurately diagnose the extent of invasion and spread of disease to nearby/distant body parts.
Positron emission tomography (PET) scan: This technique uses a radioactive substance (e.g.fluorodeoxyglucose [FDG]) that is given intravenously prior to the procedure. Cancer cells absorb larger amounts of the radioactive substance than normal cells. The areas of higher radioactivity indicate cancerous tissue on the PET scan. Thus, this technique can diagnose spread of disease to distant body parts. It is usually combined with CT scan (PET/CT).
Bone Scan: In this test, a radioactive material is injected into the vein of the patient, which gets accumulated in the areas of bones affected by the disease, which are then detected with the help of radioactivity detectors. In this way, it may help to detect the spread of cancer to bones.