Papillary Nuclear Features in Papillary Thyroid Carcinoma; a Single Centre Descriptive Cross-sectional Study

Abstract

Thyroid cancers comprise the second most common cancer among females in Sri Lanka, the commonest being papillary thyroid carcinoma (PTC). The diagnostic criteria for PTC have evolved over the years and the presence of papillary nuclear features (PNF) is now the essential criterion. A range of nuclear features are recognized as PNF but none is specific nor constantly evident in PTC. Objective: To determine the prominent PNFs in PTC diagnosed at a single histopathology centre. Methodology: This descriptive, cross-sectional study included all consecutive PTCs diagnosed over two years from 2020 at the centre. Two pathologists reviewed the H&E slides of all cases. A consensus score was given for each PNF in all cases (absent-0, only slightly expressed-1, moderately expressed-2, and well developed-3) and the average score (AS) for each PNF was calculated. Well documented 16 PNFs were assessed under three categories. Results: A total of 50 PTCs were included. AS for all seven PNFs on nuclear size and shape was ≥2 except for nuclear elongation (AS-1.64). AS for all four PNFs regarding nuclear membrane irregularities was ≥2 except for intra-nuclear pseudo-inclusions (AS-0.54). AS for all five PNFs on chromatin characteristics was <2 except for chromatin clearing (AS-2.5). Irregular nuclear placement within the cell (AS-2.76), nuclear crowding (AS-2.68), chromatin clearing and nuclear overlapping (AS-2.5) were the most prominent PNFs. Although, the presence of intra-nuclear pseudo-inclusions and multiple micro-nucleoli pushed against nuclear membrane are more characteristic of PTC, only 38.0% (19/50) and 40.0% (20/50, AS-0.68) of PTCs expressed these features. Conclusion: PNFs are expressed in different degrees in different proportions of PTCs. PNFs of nuclear size and shape and nuclear membrane characteristics are more prominent than the chromatin pattern in PTC. As the most characteristic PNFs are absent or poorly developed in the majority of tumours, the pathologist need to continue to base the diagnosis of PTC on a constellation of PNFs in order to avoid false negative diagnosis.