Clinical Thyroidology® for the Public

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What do Hürthle cells mean in thyroid nodule aspirates?

CTFP Volume 14 Issue 4

Thyroid nodules are very common and many require biopsy to evaluate the risk of cancer. Most biopsies are clear in terms of cancer (~5%) and non-cancer or benign (80-85%). However, up to 15% are determined to be indeterminate, meaning that a definite diagnosis of cancer vs benign cannot be made. This leads to additional testing and/or surgery.

Hurthle cells are a particular type of thyroid cell that can be found in both benign and cancerous thyroid nodules. Therefore, when seen in a thyroid biopsy sample, Hurthle cells often lead to an indeterminate diagnosis. Currently, the only distinction is whether a nodule is almost completely replaced by Hurthle cells (which is called a Hurthle cell neoplasm and a Bethesda class IV indeterminate nodule), or has some amount of Hurthle cells (which is then usually called either a Bethesda class III indeterminate nodule or a benign nodule depending on other benign features in the biopsy sample). Moreover, some of the additional testing of indeterminate nodules do not perform as well when there are a lot of Hurthle cells.

In this study, the authors aimed to determine the risk of cancer for each Besthesda biopsy category based on the amount of Hurthle cell change seen in the biopsy specimen.

Ren Y et al 2020 The presence of Hürthle cells does not increase the risk of malignancy in most Bethesda categories in thyroid fine-needle aspirates.

This was a study of 203 biopsy slides at a single institution where the cytology reports contained the words Hurthle cell or oncocytes (another name for Hurthle cells) and the patients had a subsequent surgery. A single senior cytopathologist reviewed all the slides and classified them as mild, moderate, or predominate Hurthle cells in the specimen. The rate of cancer was then determined for each Bethesda biopsy category (they range from I-VI) and the amount of Hurthle cells in a biopsy specimen. These were also compared to historical controls of the risk of cancer for each Bethesda category at 5 institutions.

Overall, the risk of cancer was 3% for mild Hurthle cells, 15% for moderate Hurthle cells, and 21.4% for predominant Hurthle cells. Moreover, the risk of cancer for the entire group was equal or lower for each Bethesda category except for Bethesda II/Benign biopsies. These biopsies that were classified as predominantly Hurthle cell (>75%) had a higher risk of cancer (27.3% vs 9.3%) compared to the historical control group.

In general, the presence of Hurthle cells did not change or increase the risk of cancer for biopsy specimens. This is reassuring for patients that see the words “Hurthle cells” on their biopsy report, that there is generally no increased risk of cancer.

— Melanie Goldfarb, MD


Thyroid nodule: an abnormal growth of thyroid cells that forms a lump within the thyroid. While most thyroid nodules are non-cancerous (Benign), ~5% are cancerous.

Thyroid fine needle aspiration biopsy (FNAB): a simple procedure that is done in the doctor’s office to determine if a thyroid nodule is benign (non-cancerous) or cancer. The doctor uses a very thin needle to withdraw cells from the thyroid nodule. Patients usually return home or to work after the biopsy without any ill effects.

Indeterminate thyroid biopsy: this happens a few atypical cells are seen but not enough to be abnormal (atypia of unknown significance (AUS) or follicular lesion of unknown significance (FLUS)) or when the diagnosis is a follicular or hurthle cell lesion. Follicular and hurthle cells are normal cells found in the thyroid. Current analysis of thyroid biopsy results cannot differentiate between follicular or hurthle cell cancer from noncancerous adenomas. This occurs in 15-20% of biopsies and often results in the need for surgery to remove the nodule.

Hurthle cells: are a particular type of thyroid cell that can be found in both benign and cancerous thyroid nodules.