A potential diagnostic pitfall for hobnail variant of papillary thyroid carcinoma

Kristine S. Wong, Tiffany Y. Chen, Sara E. Higgins, Brooke E. Howitt, Jochen H. Lorch, Erik K. Alexander, Ellen Marqusee, Nancy L. Cho, Matthew A. Nehs, Gerard M. Doherty, Justine A. Barletta*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

Aims: Hobnail variant of papillary thyroid carcinoma (PTC) is an aggressive PTC subtype characterised by a hobnail cytomorphology. However, some classic PTC have a ‘hobnail-like’ cytomorphology associated with thick, hyalinised, variably oedematous fibrovascular cores that appears to be a form of ischaemic/degenerative atypia. Methods and results: We studied three cohorts to compare the histopathological characteristics and clinical outcome of ‘hobnail-like’ classic PTC and true hobnail variant of PTC: cohort 1, PTC consecutively resected between 2016 and 2017 (to assess frequency of ‘hobnail-like’ cytomorphology); cohort 2, 20 ‘hobnail-like’ classic PTC resected between 2005 and 2007 (to assess clinical outcome); and cohort 3, seven true hobnail variant of PTC. A ‘hobnail-like’ cytomorphology was identified in 16% of consecutively resected PTC. Compared with true hobnail variant, ‘hobnail-like’ classic PTC occurred in younger patients (mean age 40 years versus 68 years, P < 0.001), were smaller tumours (mean tumour size 2.1 cm versus 4.4 cm, P < 0.001), had a lower rate of gross extrathyroidal extension (0% versus 71%, P < 0.001), had a lower proliferative rate (≥3 mitoses per 10 high-power fields seen in 0% versus 71%, P < 0.001; Ki67 index ≥5% in 0% versus 86%, P < 0.001), a lower rate of secondary pathogenic mutations (for cases with molecular data, 0% versus 100%, P = 0.0061) and improved survival (for cases with sufficient clinical outcome data, 10-year disease-free survival of 93% versus 0%, P = 0.0016). Conclusion: Classic PTC can show ischaemic/degenerative atypia that mimics the hobnail cytomorphology of true hobnail variant; however, these tumours lack aggressive histopathological features and pursue an indolent clinical course.

Original languageEnglish (US)
Pages (from-to)707-713
Number of pages7
JournalHistopathology
Volume76
Issue number5
DOIs
StatePublished - Apr 1 2020
Externally publishedYes

Keywords

  • hobnail variant
  • papillary thyroid carcinoma

ASJC Scopus subject areas

  • Pathology and Forensic Medicine
  • Histology

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