Occult distant metastases of well-differentiated thyroid carcinoma

The tendency of well-differentiated thyroid carcinoma to remain localized and its slow progression have supported the belief that this disease behaves as a low-grade malignancy. Consequently, a conservative approach in the management of the well-differentiated thyroid carcinoma has existed during the years. Occult distant metastases of thyroid cancer is an occasional finding considered of ominous significance.

In a retrospective study, we reviewed the records of 187 adult patients with well-differentiated thyroid carcinoma treated by total thyroidectomy. These cases were found among 1,240 thyroidectomies performed in our department between 1982 and 1993. Occult distant skeletal and lung metastases disclosed by total body 131I scans, after total thyroidectomy, were present at the time of initial treatment in 11 patients (11/187). This group included 9 women and 2 men ranging in age from 36 to 70 years, with a mean age of 47 years. Seven patients had papillary carcinoma, whereas follicular malignancy was found in four. Review of the surgical specimens showed total involvement of the gland in 5 cases, with extracapsular tumoral spread in 3 patients. Multicentric disease was present in 6 specimens. Patient follow-up revealed a mortality rate of 64% (7/11) during the first 3 post-operative years.

Analysis of this population confirms that well-differentiated thyroid carcinoma with distant metastases is an aggressive disease with lethal consequence. Early detection and therapy of occult distant metastases present at the time of initial treatment is possible only after total thyroid ablation, because otherwise the radioactive iodine is trapped by the gland's remnants.