Follicular thyroid cancer.

Follicular thyroid cancer is the second most common thyroid malignancy after PTC. There are marked geographical variations in the relative proportions of FTC and PTC, most likely related to dietary iodine content. In iodine-deficient areas, the relative rate of FTC tends to be increased. Other risk factors for FTC include age over 50 years and female sex. Genetic factors may also have a role in determining disease susceptibility but remain ill-defined. Histologically, FTC is characterized by follicle formation and the absence of any papillary elements in the tumor. Differential diagnosis from a benign adenoma can be difficult. The degree of vascular invasiveness seems to correlate with tumor aggressiveness, and two histologic subtypes, oxyphilic FTC and insular FTC, may be associated with increased morbidity and mortality. Primary treatment for FTC is complete surgical tumor removal. Extensive bilateral surgery beyond this goal may not confer additional benefit but can facilitate adjuvant treatment and follow-up. Postoperative levothyroxine treatment is almost universally used, and patients deemed at high risk of recurrence may benefit from radioiodine remnant ablation. Treatment of metastatic disease involves operation, radioiodine, and, in selected cases, external beam radiation and chemotherapy. Prognosis for patients with metastatic disease is guarded, but most other patients have good outcomes comparable to that in PTC. For nonoxyphilic FTC, high-risk features other than initial metastases include advanced age, locally extensive disease, and the presence of marked angioinvasion. In oxyphilic FTC, DNA aneuploidy is also important. Follow-up should be most intense during the first 5 years after primary treatment and needs to be tailored to the patient's risk of disease progression. For patients at low risk of recurrence (young, small lesions, minimally invasive tumor), serum thyroglobulin measurements may largely suffice, whereas higher risk patients with elevated serum thyroglobulin levels and patients with significant titers of interfering anti-thyroglobulin autoantibodies may also need to undergo periodic diagnostic radioiodine scanning.