Risk factor analysis in differentiated thyroid cancer.

Six hundred patients with primary differentiated thyroid carcinoma had follow-up studies for a minimum of 15 years and a maximum of 45 years. Recurrence rate and death rate were significantly different in defined high-risk and low-risk groups of patients. These basic risk groups were defined by age and sex alone; low risk consisted of men 40 years of age and younger and women 50 years of age and younger whereas the high-risk group were older patients. Recurrence and death rates in patients at high risk were 33% and 27% while respective figures for patients at low risk were 11% and 4%. In more recent years these results have shown significant improvement. Basic risk group definition outweighed the effect of pathologic type, local disease extension, type of treatment, and site of recurrence or metastasis. For instance, radioactive iodine cured 70% of patients at low risk with metastatic disease but only 10% of patients at high risk. Less aggressive biologic behavior of thyroid cancer before the age of menopause implies that an estrogen-rich milieu may alter the effects of initiating and promoting factors in carcinogenesis. It also suggests that therapeutic trials of estrogen be undertaken in progressive metastatic differentiated thyroid cancer.