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

Abstract Background Encapsulated follicular variant of papillary thyroidcarcinoma has recently been reclassified as noninvasive follicular thyroid neoplasmwith papillary-like nuclear featureson the basis of its highly indolent behavior, as proposed by an international group of experienced thyroidpathologists. Methods All patients from 9 high-volume endocrine surgerydepartments who underwent surgery between 2005 and 2015 and whose final surgical pathologyrevealed noninvasive follicular thyroid neoplasmwith 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 neoplasmwith 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 thyroidcarcinoma. In the group of 133 patients who underwent prophylactic lymph node dissection (37%), 1 patient had a micrometastasisbut with an associated micropapillary thyroidcarcinoma. Over a median follow-up period of 5 years, 1 patient with an associated micropapillary thyroidcarcinoma had recurrent disease at 6 years. All patients with noninvasive follicular thyroid neoplasmwith papillary-like nuclear featureswithout micropapillary thyroidcarcinoma had no lymph node metastasis or recurrent disease. Conclusion We found that noninvasive follicular thyroid neoplasmwith papillary-like nuclear featurespresents with indolent behavior. However, the identification of an associated micropapillary thyroidcarcinoma should be carefully evaluated because it could be a factor for lymph node metastasis and/or of recurrence.