Physical examination is the best way to identify early-stage thyroid cancer. Two groups of people need special screening procedures:
• Those with a family history of thyroid cancer or
  multiple endocrine neoplasia (MEN II). Serum
  thyroglobulin is useful in the former and serum
  calcitonin and carcinoembryonic antigen (CEA)
  are important tumor markers in the latter.
• Those who have had radiation therapy to the
  neck and those who have no visible thyroid lumps
  should be examined at least every two years.  A
  lump in the thyroid of these people generally
  suggests that the thyroid gland should be
  removed, since 40 percent will have cancer. To
  avoid surgery, nodules less than about 1/2 in. (1
  cm) are sometimes treated with thyroid hormone
  for six months to see if they will regress.