Reclassification as NIFTP: a Retrospective Review in a Single Institution with an Emphasis on Workload Kevin O’Hare 1 & E. O’Regan 1,2 & A. Khattak 3 & M. L. Healy 3 & M. Toner 1,2 # Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract The aim of this study was to determine the number of cases of papillary thyroid carcinoma (PTC) which could be reclassified as non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) in our institute over a 10-year period, document their clinical status and assess the number of slides that had to be reviewed per case to exclude NIFTP. The histopa- thology reports for thyroid resections for all papillary carcinoma over a 10-year period (2007–2016) were reviewed. Five hundred forty-five histopathology reports were reviewed, and 71 cases were identified as potential cases of NIFTP. Forty-nine (69%) cases had been referred from external departments and the slides were not available for review. Of the remaining 22 (31% of 71) cases, 5 were reclassified as NIFTP. The 17 cases that were not reclassified as NIFTP required review of 114 of 356 slides (median 5.5 slides per case) was required to exclude NIFTP. For the 5 NIFTP cases, 58 slides were reviewed (median 12 slides per case). We found that review of the histology reports alone was adequate for exclusion in most cases, e.g. classic PTC or EVPTC cases with documented lymphovascular invasion or capsular invasion. As a single exclusion criterion is required for exclusion from reclassification as NIFTP, this can be achieved efficiently. Two of the five patients received radioactive iodine [RAI] as per standard treatment at time of diagnosis, on the basis of tumour size. None have recurrent or metastatic disease with mean follow- up of 5.8 years. Keywords Thyroid neoplasms . Thyroid cancer . Papillary carcinoma . Papillary follicular/pathology . Reclassification . Follow-up Introduction In 2016, an international expert consensus group proposed reclassification of a subgroup of encapsulated follicular vari- ant of papillary thyroid carcinoma (EFVPTC) as a non- malignant entity, namely non-invasive follicular thyroid neo- plasm with papillary-like nuclear features (NIFTP) [1]. The diagnosis of NIFTP is based on lack of invasion along with other histological criteria which include nuclear and architec- tural features (Table 1). The diagnosis can only be made with confidence if the entire capsule of the nodule has been exam- ined. The foundation for this change had been laid with the understanding that FVPTC fundamentally consists of two types of tumours that differ in behaviour and in molecular profile [2]. Firstly, the non-invasive EFVPTC that exhibits indolent behaviour and is often associated with a molecular profile seen in follicular neoplasms, e.g. RAS type mutations among others, and secondly, the infiltrative FVPTC that may be associated with recurrence or metastasis and shows a mo- lecular profile similar to classic PTC, e.g. BRAF V600E or RET/PTC rearrangements [3, 4]. The non-malignant label of NIFTP reflects the prognosis of these tumours, allowing for less radical treatment and more appropriate clinical follow up [5–9]. Patients who have al- ready been treated for such tumours prior to the reclassifica- tion would be expected to have an excellent prognosis but are usually attending for long term follow up. The change in no- menclature has the potential to remove the psychological and financial burden and stigma that may have come with their cancer diagnosis and to reduce future surveillance. Pathologists have expressed reservations about doing such a look back exercise, with some insisting that it is always inappropriate to revisit historical diagnoses [10]. As the * Kevin O’Hare kohare@tcd.ie 1 Department of Histopathology, St. James Hospital, Dublin, Ireland 2 Department of Oral and Maxillofacial Surgery, Medicine and Pathology, Dublin Dental University Hospital, Dublin, Ireland 3 Department of Endocrinology, St. James Hospital, Dublin, Ireland Endocrine Pathology https://doi.org/10.1007/s12022-018-9538-3