Clinical presentations and treatment for 74 occult thyroid carcinoma. Comparison with nonoccult thyroid carcinoma in Taiwan.

There is limited clinical information of Chinese patients with occult well-differentiated thyroid cancer (OTC). The purposes of this study were to elucidate the clinical presentations and results of treatment in the patients with OTC in Taiwan. The data of 568 patients with pathologically verified papillary and follicular thyroid carcinomas who received primary treatment in Chang Gung Memorial Hospital were retrospectively reviewed. Seventy-four of 568 patients with well-differentiated thyroid carcinoma were OTC; those included 71 papillary thyroid carcinomas and three follicular carcinomas. Among the 74 OTC patients, five cases (6.8%) presented with distant metastases, but 41 cases (10.1%) were found with distant metastases in 416 nonoccult thyroid cancer (NOTC) (p = 0.509). In the five OTC with distant metastases, there were three papillary carcinomas and two follicular carcinomas. Only one case (1.4%) died of distant metastasis of the occult papillary thyroid carcinoma versus 20 cases out of the total 568 (4.1%) well-differentiated thyroid carcinomas. After statistical analysis, there were no differences between the survival rates of OTC and NOTC patients. In the present study, 1 month postoperative serum thyroglobulin level could be used as prognostic factor in both OTC and NOTC patients. Only 54.17% of OTC patients were diagnosed as thyroid cancer by thyroid ultrasonography with the fine needle aspiration cytology. In conclusion, most OTC had relatively benign clinical courses, but distant metastases may result in mortality still observed. Therefore, OTC should be treated as NOTC, since relatively high rate of distant metastases were found in the patients with OTC.