Why do thyroid cancers form nodules?

Cell multiplication: The thyroid has follicles. When a cell within a follicle transforms to be cancerous, it will begin to multiply faster than normal, and that follicle will grow to form a nodule. Nodules in the thyroid, however, are benign 90-95% of the time and can form for various reasons.

Cell growth: Nodules are another word for a mass. Cancers generally form masses. About 20% of the population have thyroid nodules at some point during their lives. About 70% are benign; of the remaining 30%, 80% are papillary thyroid carcinoma, which is a very low aggressive form of cancer to have. Follicular, medullary and undifferentiated carcinoma make up the rest, with some rare types.