Comparison of histopathological features and prognosis of classical and follicular variant papillary thyroid carcinoma.

Purpose: To compare the histopathological features and the outcomes of the follicular variant and classical variant of papillary thyroid carcinoma.

Material And The Methods: Demographic data, histopathological features (tumor size, thyroid capsule invasion, extrathyroidal extension, vascular invasion and multicentricity), lymph node metastasis, local recurrence, distant metastasis and mortality during the follow-up of 258 C-PTC and 153 FVPTC patients who underwent total thyroidectomy were compared. The dynamic risk assessment system was used to refine postoperative risk estimates based on the assessment of response to initial treatment.

Results: The demographic data showed no significant difference between the two groups. The mean tumor size showed no significant difference between the two groups. The rate of thyroid capsule invasion, extrathyroidal extension, and lymph node metastasis was significantly higher in C-PTC than in FVPTC group, whereas multicentricity and bilobar involvement were significantly higher in FVPTC group than in C-PTC group. Central lymph node metastasis was significantly more frequent in patients with C-PTC than in those with FVPTC (p < 0.0001). Local recurrence was found in 22 (5.3 %) patients overall and was significantly more common in C-PTC group than in FVPTC group. In patients ≥45 years, the local recurrence rate was significantly higher in patients with CPTC than in those with FVPTC. The local recurrence rate in patients <45 years was not significantly different between the two groups of patients. The multicentricity rate was significantly higher in the FVPTC group for both age groups. Dynamic risk assessment showed that the rate of intermediate- and high-risk groups showed no significant difference between C-PTC and FVPTC patients but the rate of low risk patients was higher in FVPTC group than in C-PTC group (p = 0.04). The recurrence rate in low-risk group was found higher in C-PTC compared to FVPTC patients (4.7 vs. 0.7 %, p = 0.04, respectively). The recurrence rate showed no significant difference in both intermediate- and high-risk groups in C-PTC and FVPTC patients. During the follow-up, the rate of distant metastasis and disease-specific mortality was not significantly different between the two groups (p = 0.25).

Conclusion: FVPTC is a common subtype of PTC and has a higher rate of multicentricity with bilobar involvement. Although aggressive histopathologic features, such as thyroid capsule invasion, extrathyroidal extension, and lymph node metastasis, are significantly more frequent in CPTC than in FVPTC, the long-term outcome is similar in both subtypes after appropriate initial surgery and postoperative RAI ablation treatment.