Thyroid nodules that are larger than 2 centimeters in diameter are more likely to be cancerous than smaller nodules. Multiple, small nodules are considered less likely to be cancerous than a single, large nodule, according to research published by ATA Publications on Thyroid.org.
There are many risk factors associated with thyroid cancer. Some specialists recommend a biopsy for any nodules that are greater than 1 centimeter in diameter, as explained by Thyroid.org. Other doctors perform biopsies only if nodules are greater than 1.5 centimeters in diameter, there are other lumps or nodules elsewhere in the patient's glandular system, or the patient has a family history of thyroid cancer, according to MyThyroid.com.