Can a thyroid nodule biopsy results ever be wrong?

Yes : The biopsy, usually taken by a needle, can have 4 results. Negative for malignancy, positive for malignancy, insufficient material, or indetereminate results (cant tell). And although they can be wrong, they are quite accurate most of the time. Things that can affect the accuracy is the skill of the pathologist, the presence of inflammation, size od nodule, etc.

Biopsy: Yes. Fine needle aspiration is a sensitive test for thyroid cancer but it's not 100 percent. It may get false positive or negative. Open biopsy is a more definitive way to be sure especially if a nodule is growing quickly. Seek out a good experienced board-certified endocrinologist who uses hospital-grade ultrasound for guidance.

Yes: In general, if a nodule is very large, there is a higher chance that it can be called benign although it still could be cancerous because not all of the nodule is typically cancerous. You could have one little speck of cancer that hide within the big mass and a biopsy could miss it because we can't "poke" you forever. However, if a biopsy came back "cancerous", it almost always is true.