Thyroid 101: What are the possible results of the nodule biopsy?
- Benign – This accounts for up to 70% of biopsies when using the Bethesda System (one of the most common ways that cytopathologists classify nodule biopsy specimens). The risk of malignancy in this group is typically less than 3%. These nodules are generally monitored with a follow up ultrasound within 18 months and if needed, periodically after that.
- Malignant (cancer) – This accounts for 3-7% of all biopsy specimens. The most common type of thyroid cancer seen in these biopsies is papillary thyroid cancer. When a biopsy comes back as malignant, there is a 97- 99% chance that it is truly a cancerous lesion. Almost all of these nodules will go to surgery (thyroidectomy).
- Suspicious for malignancy – When a biopsy result returns as suspicious for malignancy, there is a 60-75% chance of cancer. The cytopathologist will see features that are worrisome, but not diagnostic of a malignant or cancerous lesion. The treatment is typically surgery.
- Atypia of Undetermined Significance (AUS) or Follicular Lesion of Undetermined Significance (FLUS) – These categories may be alternatively called “indeterminate.” These specimens have some features that are worrisome and some features that look more benign. This diagnosis carries a 5-15% risk of malignancy, although there is some variability among institutions. A repeat biopsy and/or genetic testing may be useful in these cases.
- Follicular Neoplasm or ‘Suspicious for follicular neoplasm’ – This category carries a 15-30% risk of malignancy. It is difficult to tell if the nodules are a benign condition called follicular adenoma or a malignant nodule unless it is taken out. Generally, at least half of the thyroid is removed (the side with the nodule) for diagnosis and treatment.
- Non-diagnostic – This means that there are not enough cells in the sample to make a diagnosis. Despite our best efforts and even when we can see that the needle was in the nodule during the biopsy, the specimen sometimes does not have enough thyroid follicular cells to make a proper diagnosis. Non-diagnostic samples can also occur when only cyst fluid is taken out, and for other reasons, such as the presence of too much blood. In these cases, the biopsy should be repeated, and if non-diagnostic a second time, consideration is given to a third biopsy, monitoring, or surgery.