Classification Definition of<unk>  (NIFTP): A<unk><unk>  that arises from the<unk> <unk>  cells (cells that normally make<unk>  hormone), showing a predominantly<unk>  growth pattern and with<unk><unk>  of<unk> <unk>  carcinoma. There are several specific inclusion and exclusion criteria (see below). When these are met, this tumor has an extremely low malignant potential. Abbreviations: NIFTP:<unk>  EFVPTC: Encapsulated<unk>  variant of<unk> <unk>  carcinoma. PTC:<unk> <unk>  carcinoma. The new classification will be included in the World Health Organization's new Classification of Endocrine Organ Tumours, due out in 2017. Imaging findings Clinical evaluation is usually done with ultrasound studies, which will usually show a solid, well demarcated mass, often showing limited shadowing (hypoechoic). Depending on the specific character on ultrasound and other clinical findings, a fine needle aspiration is often performed. Fine needle aspiration This involves extracting a fluid sample through a thin needle inserted into the nodule (mass), and creating slides that are then interpreted by a cytopathologist. These tumors are difficult to interpret. As a result, it is<unk> ly that over 90% of these tumors will be put into one of the indeterminate categories of The Bethesda System for Reporting<unk>  Cytopathology: Recommended Diagnostic Categories The indeterminate categories of Bethesda include: * Benign * Atypia of Undetermined Significance or<unk>  Lesion of Undetermined Significance (Bethesda Category III); *<unk><unk>  or Suspicious for a<unk><unk>  (Bethesda Category IV); * Suspicious for Malignancy (Bethesda category V). * Malignant (Bethesda category IIV) It is important to note that a NIFTP diagnosis cannot be made on the basis fine needle aspiration alone. Evaluation of a surgical resection specimen is required to rule out invasive growth. If molecular studies are applied to the fine needle aspiration material, an RAS mutation is the most common identification. Pathology findings Size Tumors can be quite variable in size, ranging from as small as up to , although in general the tumors are about . The critical size threshold used to be , but supporting studies have lowered that threshold. Most tumors are seen in just one lobe of the<unk>  gland (unifocal), but multicentric tumors (same lobe or opposite lobe) can be seen in up to 38% of cases. Histologic<unk> <unk>  NIFTP tumor capsule There is no evidence of invasion of this well formed fibrous connective tissue capsule, helping to support a diagnosis of NIFTP. NIFTP tumor shows specific<unk><unk>  of<unk> <unk>  carcinoma. The<unk><unk>  of<unk> <unk>  carcinoma, but within an encapsulated<unk> : NIFTP Several specific<unk>  must be identified for the tumor to be classified in this new category, while exclusion criteria should also be evaluated. 1) Encapsulated or partially encapsulated. The tumors are usually very well delimited or circumscribed, with the majority encapsulated, surrounded by a well formed fibrous connective tissue capsule. 2) Complete absence of invasion of any kind in a tumor that has been thoroughly and carefully evaluated with the whole capsule of the lesion sampled. 3) Predominantly<unk>  pattern of growth.<unk>  structures should not be present. Further, solid, insular, or trabecular architecture must be <30% of the overall tumor for this category to still apply. Colloid (the material that<unk> <unk>  cells create) is easily identified throughout. 4) Must have the characteristic<unk><unk>  of<unk> <unk>  carcinoma, although sometimes the<unk>  are patchy in distribution without all of the tumor showing those<unk> . The<unk><unk>  can be divided into three main categories: *<unk>  size and shape:<unk>  enlargement,<unk>  elongation, and<unk>  overlapping and crowding. Loss of<unk>  polarity, with nuclei at the lumen, middle, or basal zone of the cells is also a helpful finding. *<unk>  membrane irregularities: irregular<unk>  contours,<unk>  grooves and folds, "rat-bites" or demi-lune formations, and the presence of intranuclear cytoplasmic inclusions. *<unk>  chromatin characteristics:<unk>  chromatin clearing, often with condensation or margination along the<unk>  membranes, resulting in accentuated<unk>  margins, glassy nuclei, or fine, even delicate, powdery<unk>  chromatin. These<unk>  have been recently validated by an international group of practicing general surgical pathologists, showing a substantial interobserver agreement with applying a<unk>  Standardized Scoring System. Exclusion criteria 1) Any invasion. 2) The presence of any other<unk> <unk>  carcinoma variant (examples would include tall cell, columnar cell, cribriform morular, diffuse sclerosing, etc.). 3) True<unk>  structures (a fibrovascular core surrounded by<unk> ic cells). While originally limited to <1%, newer data suggests no<unk>  structures should be allowed. 4) Psammoma bodies. These are calcified remnants of<unk>  structures, and thus if a psammoma body is present anywhere within the tumor (in the correct location), then a NIFTP cannot be diagnosed. 5) Tumor necrosis: If there is true tumor necrosis not associated with a fine needle aspiration. 6) Increased mitoses: If there are ≥3 mitoses per 10 high-power fields, then this category cannot be used.
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