Needle Biopsy of Thyroid Masses Misidentifies 50% of Thyroid Cancers!

Surgeons at the University of Wisconsin found that fine needle aspiration biopsy (FNAB) in 26 of 52 FNAB reported as benign (50.0%) turned out to be either neoplastic (22) or malignant (4) on final pathologic analysis after thyroidectomy. Among patients with nondiagnostic FNAB results, the risk of malignant neoplasms was 27.3%.

Even for smaller thyroid masses, FNAB is still not 100% accurate with a falsely negative rate of around 10%. Why is that?

Well, one must keep in mind that the FNAB samples (or removes) only a tiny tiny tiny part of the thyroid mass (think of a needle going into an apple and trying to hit the worm in the middle). Should the needle sample a part of the thyroid cancer mass where no cancer is present, it will come back normal, even if it is truly cancer.

What does this mean for a patient with a thyroid mass?

1) The ONLY way to know 100% whether a patient has thyroid cancer or not is to remove the thyroid.
2) IF the FNAB shows thyroid cancer, total thyroidectomy is recommended.
3) IF the FNAB does not show thyroid cancer, thyroid cancer can STILL be there; it's just that the FNAB was just plain wrong. Thyroid lobectomy should still be considered.

Of course, one needs to talk with your local surgeon on what the next step is.

Just keep in mind that the FNAB is not 100% accurate!

Reference:
Accuracy of Fine-Needle Aspiration Biopsy for Predicting Neoplasm or Carcinoma in Thyroid Nodules 4 cm or Larger. Arch Surg. 2009;144(7):649-655. doi:10.1001/archsurg.2009.116.

False negatives in thyroid cytology: impact of large nodule size and follicular variant of papillary carcinoma. Laryngoscope. 2013 May;123(5):1305-9. doi: 10.1002/lary.23861. Epub 2013 Jan 4.