NIFT-P: Are they indolent tumors? Results of a multi-institutional study.

Background: Encapsulated follicular variant of papillary thyroid carcinoma has recently been reclassified as noninvasive follicular thyroid neoplasm with papillary-like nuclear features on the basis of its highly indolent behavior, as proposed by an international group of experienced thyroid pathologists.

Methods: All patients from 9 high-volume endocrine surgery departments who underwent surgery between 2005 and 2015 and whose final surgical pathology revealed noninvasive follicular thyroid neoplasm with papillary-like nuclear features (>10 mm) were included in this study. The primary outcome was to determine the potential for recurrent disease in these patients.

Results: Among the 363 patients with noninvasive follicular thyroid neoplasm with papillary-like nuclear features, 76% were female with a median age of 50 years (5-86 years); 345 patients (95%) underwent total thyroidectomy. A total of 65 patients had an associated micropapillary thyroid carcinoma. In the group of 133 patients who underwent prophylactic lymph node dissection (37%), 1 patient had a micrometastasis but with an associated micropapillary thyroid carcinoma. Over a median follow-up period of 5 years, 1 patient with an associated micropapillary thyroid carcinoma had recurrent disease at 6 years. All patients with noninvasive follicular thyroid neoplasm with papillary-like nuclear features without micropapillary thyroid carcinoma had no lymph node metastasis or recurrent disease.

Conclusion: We found that noninvasive follicular thyroid neoplasm with papillary-like nuclear features presents with indolent behavior. However, the identification of an associated micropapillary thyroid carcinoma should be carefully evaluated because it could be a factor for lymph node metastasis and/or of recurrence.