Non-invasive Thyroid Follicular Neoplasm

 
Papillary thyroid cancer (PTC) is the most common histologic thyroid cancer in children. Follicular thyroid carcinoma (FC) is the second most common thyroid cancer in children occurring less than 5% of the time. FC is associated with TSH elevation, iodine deficiency areas and radiation exposure. FC is a tumor composed of neoplastic follicles rather than papilla but with follicular cells showing nuclear features characteristic of papillary thyroid carcinoma. Two subtypes of FC are recognized: encapsulated or minimally invasive FTC and widely invasive FC. Encapsulated FC has increased its incidence during the past 10 years. It is a tumor with an indolent behavior. In 2012 the National Cancer Institute revised this pathology and determined to call it Non-invasive follicular neoplasm with papillary-like nuclear features (NIFTP) if it reflected the following characteristics: follicular growth pattern, lack of invasion, nuclear features of papillary carcinoma comprising less than 1% of the tumor, absent psammoma calcifications, the lesion had clonal origin determine by findings a driver mutation (biologically a neoplasm) and a very low risk of adverse outcome. NIFTP also has a lack of common somatic mutation like BRAF and/or RAS. Studies have found that NIFTP has a low recurrent rate over the years, low metastatic rate, can be managed with lobectomy only obviating the need for completion thyroidectomy and subsequent radio-iodine therapy. This proposed reclassification will reduce overtreatment of this condition and the psychological and clinical consequences associate with a diagnosis of cancer. NIFTP is a surgical disease and its diagnosis can only be rendered upon excision and depends totally on adequate or entire sampling of the interface between tumor and its capsule/periphery to exclude invasive characteristics. To ensure a lack of infiltrative or invasive growth the entire tumor capsule/periphery should be submitted for histologic evaluation. A diagnosis of NIFTP cannot be rendered using fine needle aspiration cytology only. Lymph nodes metastasis are incompatible with NIFTP.

References:
1- Zou CC, Zhao ZY, Liang L: Childhood minimally invasive follicular carcinoma: Clinical features and immunohistochemistry analysis. J Paediatr Child Health. 46(4): 166-70, 2010
2- Nikiforov YE, Seethala RR, Tallini G, et al: Nomenclature Revision for Encapsulated Follicular Variant of Papillary Thyroid Carcinoma: A Paradigm Shift to Reduce Overtreatment of Indolent Tumors. JAMA Oncol 2(8): 1023-1029, 2016
3- Baloch ZW, Seethala RR, Faquin WC, et al: Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features (NIFTP): A Changing Paradigm in Thyroid Surgical Pathology and Implications for Thyroid Cytopathology. Cancer Cytopathol. 124(9): 616-620, 2016
4- Rossi ED, Mehrotra S, Kilic AI, et al: Noninvasive Follicular Thyroid Neoplasm with Papillary-Like Nuclear Features in the Pediatric Age Group. Cancer Cytopathol. 126(1): 27-35, 2018
5- Hung YP, Barletta JA: A user's guide to non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP). Histopathology 72: 53-69, 2018
6- Poller DN, Nikiforov YE: Non-invasive follicular thyroid neoplasm with papillary-like nuclei: reducing overtreatment by reclassifying an indolent variant of papillary thyroid cancer. J Clin Pathol . 2016 Jul 7. Pii: jclinpath-2016-203930.
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