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Managing Thyroid Tumors Diagnosed as NIFTP, Endocr Pract. 2017;23(No. 9)

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Fig. 1. NIFTP: Low-power view showing a thinly encapsulated noninvasive follicular patterned nodule ( A - B ) comprised of macro- and microfollicles lined by cells showing papillary-like nuclei ( C ). NIFTP = noninvasive follicular thyroid neoplasm with papillary-like nuclei.

Fig. 2. A cartoon depiction of diagnostic criteria for encapsulated follicular lesions of the thyroid gland: follicular adenoma, follicular carcinoma, NIFTP, and the follicular variant of papillary thyroid carcinoma ( lightest blue, black asterisk = tumor capsule, medium blue = tumor, red asterisk = tumor cells without nuclear features of PTC, darkest blue = invasive tumor). The follicular adenoma is encapsulated and shows no invasion ( A ), whereas the follicular carcinoma shows tumor cells invading into or beyond the tumor capsule (red arrows) and/or showing vascular invasion into the capsular vessels ( black arrow, B ). The NIFTP is an encapsulated tumor that shows PTC-like nuclei without invasive characteristics ( C ). The encapsulated follicular variant of PTC shows nuclear features of PTC and invasion into or beyond the tumor capsule ( red arrows ) and/or vascular invasion ( black arrows, D ). NIFTP = noninva- sive follicular thyroid neoplasm with papillary-like nuclei; PTC = papillary thyroid carcinoma. A B C D

The diagnosis of NIFTP be made with strict adherence to the following inclusion and especially to, exclusion histo- morphologic criteria (18) (Table 1, Fig. 1 and 2). As mentioned above, the renaming of noninvasive EFVPTC to NIFTP may prove to be beneficial to patients; however, it may also raise the following questions for both clinicians and patients: Invasive Characteristics The diagnosis of tumor capsule invasion can be a diffi- cult task for the surgical pathologist, partly due to lack of consensus among experts in defining the diagnostic crite- ria (8). Various criteria have been cited in the literature for the diagnosis of invasion into the tumor capsule (8). Some debate the importance of capsular invasion in the absence of vascular invasion (20). Since it has been associated with metastatic disease, any form of invasion by the tumor cells

into its capsule (usually traversing the entire thickness of capsule) or into the surrounding normal thyroid parenchy- ma should exclude the diagnosis of NIFTP. Multifocal Tumors and Staging The diagnosis of NIFTP does not preclude the diagno- sis of another distinct tumor(s) in the thyroid gland. Cancer staging in such cases should not include NIFTP lesions. Tumor Size The NIFTP proposal study did not include tumors measuring <1.0 cm; however, a recent study has shown that these tiny tumors can be included in the new category (21). A recent study by Xu et al demonstrated that NIFTP tumors measuring ≥4.0 cm appear to have an extremely low risk of recurrence, even when treated with conservative surgi- cal treatment without radioiodine therapy (22). However,

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