Follicular thyroid carcinoma with capsular invasion alone: A nonthreatening malignancy

Background. The study was designed to determine whether invasion of the tumor capsule, in the absence of vascular invasion (VI), was significant in predicting cause-specific mortality in follicular thyroid carcinoma (FTC). Methods. Seventy-two patients with FTC were treated by us during 1971 through 1985. In 65 cases the tumors could be classified as either showing capsular invasion (CI) alone (20) or VI, with or without CI, (45). Median follow-up of 45 survivors was 11 years; 12 patients died of FTC. Results. The 10-year occurrence rates for cause-specific mortality and distant metastases were 28% and 19%, respectively, for patients with VI. Comparable rates for the patients with CI were 0% (p = 0.019) and 0% (p = 0.052), respectively. By univariate analysis, higher rates of cause-specific mortality were significantly associated with distant metastases at diagnosis (p < 0.0001), the presence of VI (p = 0.019), and moderate or marked microinvasion (p = 0.019). In stepwise multivariate analyses, only distant metastases at diagnosis had independent prognostic significance (p < 0.0001) in the prediction of cause-specific mortality. In a Cox model, adjusting for distant metastases at diagnosis, the presence of VI was of borderline significance (p = 0.06) in predicting cause-specific mortality. Conclusions. FTC, diagnosed on the basis of CI alone, did not result in either distant metastases or cancer-related death. The dominant determinant of cause-specific mortality was the presence of distant metastases at diagnosis.