Further evidence of the validity of risk group definition in differentiated thyroid carcinoma.

Three hundred nine consecutive patients primarily treated at the Lahey Clinic Foundation for differentiated thyroid carcinoma between the years 1961 and 1980 were followed for a median of 13 years and a minimum of 5 years. The recurrence and survival rates of these patients are strikingly different in the low-risk group (men 40 years of age and under and women 50 years and under) compared with the high-risk group (all older patients). Only two patients died and eight others had recurrences but survived in 192 low-risk patients, whereas 18 died and 23 had recurrences in 117 high-risk patients. Thus 20% of patients with recurrence in the low-risk group died but 78% of patients with recurrence in the high-risk group died. Follicular carcinoma and major capsular invasion carries a poor prognosis, but only 22% of low-risk in contrast to 55% of high-risk patients died. The fact that low- and high-risk patients have a separate biology is emphasized by unique sex ratio differences. Low-risk patients have a constant male to female ratio of about 5:1, whereas high-risk patients have progressively increased from 1:3 to a male predominance during the past 5 decades. This study showing unique differences in results by age reemphasizes the concept of basic risk groups in differentiated thyroid cancer. The effect of this basic risk group, as in our previous report, supercedes the effect of pathologic type, extent of local disease, or aspects of therapy and exerts principal control over biologic behavior.