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A test tube, saffron ultrasound arcs crossing a wide thyroid gland, and a thin needle entering a nodule within it.

Diagnosis of Thyroid Cancer

5 of 6~2 min readReviewed

Thyroid Nodular Diseases and Thyroid Cancer

The diagnosis of thyroid cancer rests on three things: biochemical tests, ultrasound imaging and fine needle aspiration.

In the panel of biochemical tests, the purpose is mainly ruling out benign conditions, so the parameters that are measured should evaluate thyroid function, malignancy and autoimmune thyroid disease, and they are:

  • TSH
  • T4 and T3
  • antibodies against thyroid peroxidase (TPO), an enzyme of hormone synthesis, and against thyroglobulin (Tg), a protein made by follicular cells
  • Tg level in serum
  • Calcitonin — for screening of medullary thyroid carcinoma, or MTC; routine measurement in every nodule is not firmly recommended, because of false positives and uncertain benefit

Results of that panel can point to other causes of thyroid nodules:

  • if the TSH level is normal and calcitonin is also normal, this points to non-toxic MNG
  • if TSH is low and thyroid hormones are increased and calcitonin is normal, this points to toxic MNG
  • positive antibodies for the thyroid gland point to autoimmune thyroid disease, or AITD

The American Thyroid Association, or ATA, made a guideline for performing fine needle aspiration (FNA), which samples cells from the nodule with a thin needle, based on the ultrasound findings. Both the sonographic pattern and the size of the nodule set the threshold: a nodule with a highly suspicious pattern is sampled from 1 cm upward, an intermediate-suspicion nodule also from 1 cm, a low-suspicion nodule from 1.5 cm, and a very-low-suspicion nodule from 2 cm, while a nodule with a benign pattern is not sampled.

A left-to-right row of five nodule panels: a thin needle enters the first four as the nodule grows from 1 cm to 2 cm, while the last smooth nodule has no needle.
Biopsy thresholds by sonographic pattern: highly or intermediate suspicion from 1 cm, low from 1.5 cm, very low from 2 cm.

What is done with the result — observation of a benign nodule, or surgery and further treatment for a cancer — follows from the behaviour and the risk of the nodule, not from the biopsy alone.