Long-term results and prognostic factors in patients with differentiated thyroid carcinoma

Abstract

A multivariate analysis of the prognostic factors was carried out on a series of 546 differentiated thyroid cancers followed for 8 to 40 years. For survival, the highest risk factor was associated with age; tumors diagnosed in patients younger than 45 years had higher relapse-free survival (RFS) and total survival (TS) rates and a slower growth rate. In children, although the RFS and TS at 15 years were high, they decreased later. The second independent prognostic factor was histology. There was no difference between papillary and follicular well-differentiated (FWD) tumors, but follicular moderately differentiated (FMD) had lower TS and RFS. Among FMD cancers, relapses occurred earlier and the interval between relapse and death was shorter. The third factor was sex. Tumors tended to disseminate more in male than in female patients. The survival rate after relapse was the same, however, suggesting that the growth rates are not different. The presence of palpable lymph nodes also had a significant independent impact on both TS and RFS. Patients treated after 1960 have a better outcome than patients treated earlier, although they did not differ in age distribution, histologic characteristics, sex ratio, or incidence of palpable lymph nodes. The distribution of time intervals between treatment and relapse was not compatible with an exponential failure time model but fit with a log-logistic model. Relapses can occur as late as 30 years or more after initial treatment. Elevated levels of circulating thyroglobulin have been observed in about 12% of the patients who had been in complete remission for longer than 20 years.