The follicular-variant subtype of papillary thyroid cancer may be subdivided into subtypes with different characteristics
The background of the study. One subgroup of thyroid cancer consists of tumors called follicular variant of papillary cancer (FVPTC). These tumors have some features of papillary cancers, such as lack of a capsule, but others are encapsulated, like follicular cancers. This study was done to determine the relative frequency and course of these two subgroups of FVPTC.
How the study was done. The study group consisted of 78 patients who had a FVPTC, as defined by the presence of follicles lined by cells with the nuclear features of papillary cancer and the absence of papillary architecture, that was >1 cm in longest dimension. The tumors were characterized as encapsulated if they were completely surrounded by a capsule, with or without foci of capsular or vascular invasion, and nonencapsulated (infiltrative), if there was little or no capsule. The patients’ records were reviewed to obtain information about extent of surgery, operative findings, other treatment, and outcome.
The results of the study. The 78 patients with FVPTC included 59 women and 19 men. The tumor was 4 cm in 88 percent of the patients and >4 cm in 12 percent, and it was encapsulated in 78 percent and infiltrative in 22 percent. Most patients were treated by removal of only the side of the thyroid with the nodule (thyroid lobectomy). The characteristics of the patients with encapsulated and infiltrative tumors and the pathologic characteristics of the tumors were similar, except that the tumor had spread outside the thyroid more often in the patients with infiltrative FVPTCs.
Sixty-nine patients were followed for >1 year (range, 1 to 21). None of the patients with a noninvasive encapsulated FVPTC had a recurrence of their tumor, including 31 patients treated by thyroid lobectomy alone. Among 13 patients with invasive encapsulated tumors, 1 had a recurrence, and among 14 patients with infiltrative tumors none had a recurrence.
The conclusions of the study. The follicular variant of papillary thyroid cancer occurs in two forms. Most are encapsulated tumors that do not spread, and may not be cancers at all, whereas others are infiltrative tumors that resemble papillary cancers.
The original article. Liu J, Singh B, Tallini G, Carlson DL, Katabi N, Shaha A, Tuttle RM, Ghossein RA. Follicular variant of papillary thyroid carcinoma: a clinicopathologic study of a problematic entity. Cancer 2006;107:1255-64.