Thyroid follicular carcinoma is the second most frequent type of thyroid cancer after papillary carcinoma. It is derived from the follicular cells of the thyroid gland.
Thyroid follicular carcinoma accounts for about 5%–10% of all cases of differentiated carcinoma, but preoperative diagnosis by cytology is impossible. It is necessary to histologically confirm at least capsular invasion, vascular invasion, or metastasis for differentiating thyroid follicular carcinoma from follicular adenoma, which is a benign tumor, and preoperative diagnosis is difficult. In addition, cases with the diffuse invasive type of carcinoma and distant metastasis are considered to have a poor prognosis, but the invasion type can also be confirmed only pathological diagnosis after surgery, so that the prognostic factors before surgery are not clear.
We investigated the preoperative predictors of distant metastasis in cases of follicular carcinoma.
In 14 patients diagnosed as having thyroid follicular cancer and treated at our department from January 2010 to December 2020, we investigated the age, primary tumor diameter, preoperative diagnosis, preoperative serum thyroglobulin level (Tg), invasion type (microinvasive or diffuse invasive), presence/absence of vascular invasion, presence/absence of distant metastasis at initial diagnosis, and treatment for distant metastasis.
Consistent with previous reports, age, invasion type, and presence/absence of vascular invasion were significantly associated with the risk of distant metastasis. When the serum Tg was examined in detail as a predictor of the risk of distant metastasis among the items that were evaluable preoperatively, we found a clear trend of higher preoperative serum Tg levels in patients with distant metastasis. Also, the t-test showed a significant association of the preoperative serum Tg and the presence of distant metastasis. We hypothesized that the serum Tg is a useful preoperative predictor of the risk of distant metastasis in cases of follicular carcinoma, and patients with follicular tumors with serum Tg levels greater than 500 ng/ml should be aggressively operated upon.
