Encapsulated non-invasive follicular variant of PTC was reclassified as NIFTP in 2016 , and was included in the WHO Classification of Tumours of Endocrine Organs in 2017  as a separate entity, acknowledging its very low malignant potential. However, Ferris et al  recommend considering NIFTP as a preneoplastic lesion. Therefore, and considering that the reclassification is a recent event, strict follow-up is endorsed until further evidence is gathered. (aca necesitamos una cita)
Prevalence of NIFTP in our series was 1.12%, (30/2677), thus being among the lowest reported. Similar findings were found in Korea (0.18% (2/1411 PTC), Japan (0.5% (54/10176) and Canada (2.1% (102/4790) [9, 10, 11]. In a multi-institutional series from Southern Europe, the rate was 5.2%, but was highly variable in neighbouring institutions, ranging from 0 to 12.1%, suggesting pathologist’s interpretation of nuclear alterations as the main cause of these differences . A meta-analysis including seven series showed that the incidence of NIFTP was 1.6% in different Asian populations. This is significantly lower than the incidence found in non-Asian series, which can be as high as 15% . Dissimilarities may be due to environmental and ethnic differences, as well as the thorough examination and strict criteria for diagnosing NIFTP that the samples in our series were submitted to. Also, in some countries, fear of malpractice claims can modify the histological thresholds, leading many pathologists to diagnose malignancy in equivocal lesions ,
Although widespread adoption of the new NIFTP terminology was anticipated, reports of NIFTP on cancer registries failed so far to confirm this. Kitahara et al.  in 2017 informed that the observed number of NIFTPs recorded in SEER-18 accounted for only 1.3% of the number of total PTCs, much lower than the estimated proportion predicted by Nikiforov et al. (18.6%). Furthermore, a recent study including 3368 pathology reports from six countries found that the prevalence of NIFTP among papillary thyroid cancer cases was 4.8%. No substantial changes in the frequency of diagnosis of NIFTP were found from 2016 to 2019 .
Regarding cytological evaluation of NIFTP, it was suggested that there are certain characteristics, such as hypercellularity, sheet-like architecture, follicular pattern, follicular microarchitecture and nuclear score that point towards the diagnosis [17, 18]. However, in order to establish an accurate diagnosis of NIFTP, the indemnity of the tumor capsule needs to be fully assessed and lympho-vascular invasion should be ruled out, and this cannot be estimated exclusively on the information yielded by FNA . Additionally, even if psamomma bodies and papillae are exclusive of PTC, other nuclear features are shared between NIFTP and PTC [7, 18, 20]. In our series, only 9% of the cases had cytologic diagnosis corresponding to the categories III and IV of the BSRC. This is in contrast with other results, showing that the prevalence of these categories may reach to 58% . The impact of changes in the predictive value for malignancy of ultrasonography, cytology, molecular tests or even fluorodeoxyglucose positron emission tomography (FDG-PET) depend on the prevalence of NIFTP in the population (22]. As we found only 1.12% of NIFTP in our multicentric study in Argentinian patients, no substantial changes on the relative malignancy rate of each of the Bethesda system for reporting thyroid cytology (TBSRTC) categories should be expected with the introduction of NIFTP in the classification of thyroid tumors in Argentina.
All of the patients included in this series were treated with total thyroidectomy. Over half of them also were submitted to radioiodine ablation, according to usual practices before the reclassification of these tumors as NIFTP [23, 24]. Currently, radioiodine ablation in NIFTP is not recommended. Surgery remains the therapy of choice, as NIFTP is considered a preneoplastic lesion, and definitive diagnosis needs the complete histologic assessment of the tumor. Hemithyroidectomy is the preferred surgical approach, providing there are no lesions in the contralateral lobe, as recommended by the American Thyroid Association guidelines . However, Katsakhyan et al.  did not find significant changes in the number of total or partial thyroidectomies performed as initial surgeries comparing a pre- to a post-NIFTP cohort. Perhaps more time is needed to show changes, as a significant increase in the rate of hemithyroidectomies was found when comparing surgical treatment of thyroid cancer before or after the release of the 2015 American Thyroid Association Guidelines .
As for follow up, since NIFTP was only recently established as a diagnostic entity, it was suggested that an occasional neck ultrasound and annual measurements of thyroglobulin and anti-thyroglobulin antibodies should be performed until more clinical experience is obtained . In contrast, Rosario argues that if patients with NIFTP continue to be followed up like those with low risk PTC, the practical impact promoted by these changes would have been minimal or none .
Molecular biology studies were performed in 19 cases (63%). RAS mutations were the most frequent finding and were identified in 4 tumors (13%). This is in coincidence with other studies, in which overall prevalence of RAS mutations ranges from 10-67% [1, 27, 28]. This genetic profile is similar to the one found in other follicular lesions (such as PVCPT, follicular adenoma and follicular carcinoma), and differs from the usual molecular findings in classic PTC, further warranting the reclassification of NIFTP as a different entity. In our series, HRAS and NRAS mutations were equally frequent (6.5% each), in contrast with other reports, in which HRAS mutations comprise between 25-50% of cases [1, 27–34] being NRAS mutations the most usual [27, 28, 35, 36].
The original diagnostic criteria for NIFTP were proposed in 2016 , and then modified in 2018  stating that the presence of any true papillary structure would rule out the diagnosis of NIFTP. In addition, if molecular testing (which is not mandatory) is performed, the presence of high-grade mutations, such as TERT, BRAF V600E, or RET/PTC rearrangements would exclude the diagnosis of NIFTP. This item raises the practical question of whether NIFTP can be diagnosed without molecular biology techniques, which are not routinely available in Argentina.
Additionally, an accurate differential diagnosis of NIFTP from encapsulated FVPTC requires, besides routine BRAF mutation testing, a complete assessment of the tumour (and not only the capsule) to rule out the presence of papillae . This places higher demands on the pathologists (both in terms of time and expertise), and also may lead to further diagnostic confusion and increasing costs (due to mandatory molecular studies). The benefits are therefore unclear, as both entities share a similar clinical behaviour. Further studies with longer follow up are needed to elucidate these questions.
In conclusion, NIFTP prevalence in this series was among the lowest reported. Excellent response to initial treatment confirms the indolent behaviour of these neoplasms, which will probably lead to a more conservative management, avoiding unnecessary expenses for the health care system, and reducing emotional distress for patients with this diagnosis. Molecular findings differ from other series, which may be related to stringent criteria for diagnosing NIFTP and/or, to environmental or ethnic features of our population.