A lump in the front of the neck
Changes in voice, hoarseness
Swollen lymph nodes in the neck
Difficulty in breathing or swallowing
Pain in the neck
Over exposure to radiations has been proven to multiply the risk to catch a thyroid cancer. Treatment with x-rays is the most common source. There is little reason to panic. Routine x-ray investigations use low doses of radiation. Repeated exposures are to be dealt with caution since these are harmful.
If anyone else in the family had/has thyroid cancer:
Medullary thyroid cancer runs in families. It is associated with a change in a gene called RET. This change gets transferred from parent to child. This cancer may occur alone (called the Familial Medullary Cancer of thyroid) or in the company of other cancers (The group of cancers is called Multiple Endocrine Neoplasia, abbreviated as the MEN syndrome).
Other diseases that run in family:
A family history of goitre (meaning swollen thyroid gland) with multiple thyroid nodules may predispose individuals to papillary thyroid cancer. People with a family history of growths in the colon or rectum (Familial polyposis) are also at risk of the same.
People with a goitre or benign thyroid nodule are at high risks
Ages above 45 are at increases risks of acquiring thyroid cancers.
As I had mentioned earlier females are thrice more predisposed to the risk of developing thyroid cancers. In women factors like a late child birth (above an age of 30) and use of oral contraceptive pills may also have an association with cancers of thyroid gland.
Iodine as a risk factor is still under study. Evidences available are confusing. Too little iodine in diet may increase the risk of follicular cancer while too much of iodine breeds the risk of papillary cancer. Many of those who migrated from iodine poor regions to iodine rich regions have shown decreased trends of acquiring follicular cancer. Too much iodine in diet has been related to a higher incidence of papillary cancer in South India.
Findings from Iceland and Norway suggest an association with consumption of excess shellfish and other seafood.