How do health care professionals diagnose thyroid cancer?
The diagnosis of thyroid cancer often occurs before symptoms develop, when a lump is discovered in the thyroid gland. This may occur on routine physical exam of the neck by a health care provider, or it may be found by the patient.
Once a lump in the thyroid is discovered, it is important to know whether it is benign or malignant (cancerous).
An ultrasound usually is performed to assess whether there is a single nodule or whether multiple nodules are present. Ultrasound can determine whether the nodule is fluid filled or solid. Ultrasound also can determine the general appearance of thyroid looking for inflammation or irregularities and the presence of nearby enlarged lymph nodes that may represent metastatic cancer.
Fine needle aspiration biopsy (FNAB) is usually the next step. It is a procedure performed to obtain a sample of cells from the nodule to determine if it is cancerous. Using ultrasound, a thin needle is placed into the nodule and cells from the nodule are obtained. These cells can be examined under a microscope by a pathologist to determine whether a cancer is present and if so, what type of cancer it is.
Sometimes, the results of the aspiration are unclear or indeterminate, and the aspiration may need to be repeated to get a better sample and more cells to study.
Guidelines developed by the American Thyroid Association help the provider interpret the results of the ultrasound and fine needle aspiration biopsy. When evaluated together, the test results give direction as to whether the nodule is benign or malignant (cancerous), and help inform the choice of treatment options.
Radio-iodine testing may be considered if the results of the FNAB don’t provide a definite answer as to whether a nodule is benign or malignant. The patient swallows some radioactive iodine which is taken up by the thyroid gland. The gland is scanned by a Geiger counter-type apparatus that determines how much radioactive iodine has been taken up by the thyroid gland and any thyroid nodules. If the nodule picks up much of the iodine, it is referred to as a “hot nodule.” Hot nodules are rarely cancerous. Nodules that take up little to no iodine are referred to as “cold nodules.” Although the overwhelming majority of cold nodules are benign, 5% turn out to be malignant.
Although thyroid scans may be helpful, it is not a first-line test and fine needle aspiration of the gland is a much more useful test. There is an exception. In the patient with a thyroid nodule whose TSH (thyroid stimulating hormone) level is low, the next step may be a radio-iodine test. The risk for cancer in a patient who is hyperthyroid (low TSH) and who has a “hot nodule” is very low and biopsy may not be required.
Blood tests may be ordered to determine the function of the thyroid gland. Measuring blood levels of thyroid-stimulating hormone (TSH) secreted by the pituitary gland turns out to be very effective in determining thyroid function, including whether the patient is hyperthyroid or hypothyroid.
Calcitonin levels may be increased in medullary thyroid cancer (MTC), but because MTC is very rare, this test is not recommended to screen for cancer.
MTC, FMTC, and MEN are hereditary cancers. Genetic testing may be done in family members of people with these types of cancers. As well, other blood tests may be ordered, including CEA, RET proto-oncogene, calcium, and calcitonin. Screening for other associated diseases might include tests looking for a tumor known as pheochromocytoma.
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