Cancer of the thyroid is the most common endocrine malignancy. Thyroid neoplasms arising from follicular cells (adenoma, carcinoma, and follicular/papillary carcinoma) show a broad range of overlapping clinical and cytologic features. A clear distinction between benign and malignant disease based solely on cytological examination of a needle biopsy specimen may be difficult. For this reason, a surgical procedure to remove all or a large portion of the thyroid gland may be necessary to obtain sufficient tissue for a definitive diagnosis of follicular thyroid cancer. Pathological examination showing capsular or vascular invasion may be required for this determination.
Follicular thyroid carcinoma (FTC) is a well-differentiated tumor. In fact, FTC resembles the normal microscopic pattern of the thyroid. FTC originates in follicular cells and is the second most common cancer of the thyroid, after papillary carcinoma. Follicular and papillary thyroid cancers are considered to be differentiated thyroid cancers; together they make up 95% of thyroid cancer cases.
Papillary/follicular carcinoma must be considered a variant of papillary thyroid carcinoma (mixed form), and Hurthle cell carcinoma should be considered a variant of FTC.
Thyroid cancers are found more often in patients with a history of low-dose or high-dose external irradiation to the cervical or thyroid area. The most common thyroid tumor to develop after exposure to radiation is papillary thyroid cancer. Patients whose thyroid cancer has developed following radiation to the head and neck area may present with more extensive disease. Overall, about 5% of patients with thyroid cancer have metastases beyond the cervical or mediastinal area on initial presentation, as do 2-3% of patients with papillary thyroid cancer and 11% of patients with follicular thyroid cancer. Some 5-10% of patients with thyroid cancer will die of their disease.
Despite its well-differentiated characteristics, follicular carcinoma may be overtly or minimally invasive. In fact, FTC tumors may spread easily to other organs. Life expectancy of affected patients is related to their age; the prognosis is better for younger patients than for patients who are older than 45 years. Patients with FTC are more likely to develop lung and bone metastases than are patients with papillary thyroid cancer. The bone metastases in FTC are osteolytic. Older patients have an increased risk of developing bone and lung metastases.
Current National Comprehensive Cancer Network (NCCN) guidelines recommend lobectomy plus isthmusectomy as the initial surgery for patients with follicular neoplasms, with prompt completion of thyroidectomy if invasive FTC is found on the final histologic section. The NCCN recommends total thyroidectomy as the initial procedure only if invasive cancer or metastatic disease is apparent at the time of surgery, or if the patient wishes to avoid a second, completion thyroidectomy should the pathologic review reveal cancer.[1]
In a study by Asari et al of 207 patients with FTC, the 127 patients with minimally invasive growth had no lymph node metastases. According to the authors, total thyroidectomy is recommended for all patients with FTC, but patients with widely invasive FTC need more aggressive surgery because of a higher tendency toward lymph node metastases. Patients with minimally invasive disease have an excellent prognosis with a limited need for nodal surgery, according to this study.[2