Distinctive hobnail subtype of papillary thyroid carcinoma: a case series and short review of literature.

Abstract

Introduction: The hobnail subtype of papillary thyroid carcinoma (HSPTC) is a rare and aggressive subtype, comprising 1-2% of all PTC cases. It is characterized by poor prognosis, frequent BRAF and p53 mutations, and a high recurrence rate. Given the limited data on HSPTC, especially in the Indian population, this case series aims to provide valuable insights into its clinical behavior, mutational profile, and treatment outcomes.

Materials and methods: A retrospective analysis was conducted from January 2021 to December 2023. Histological reports were reviewed for cases with ≥ 5% hobnail features. Cases fulfilling these criteria were reviewed for features of high-grade differentiated thyroid carcinoma. Immunohistochemistry was performed to identify BRAF.V600E and p53. Patient demographics, tumor characteristics, and follow-up data were collected. Follow-up included clinical exams, thyroid function tests, thyroglobulin, anti-thyroglobulin antibody levels, and imaging when necessary.

Results: Among 600 PTC cases, 4 were identified as HSPTC (0.67% incidence). The median follow-up was 40 months. Mean tumor size of 3.3 cm. 75% showed BRAF and p53 positivity. Lymphovascular invasion (LVI) was present in 50% of patients. Recurrence occurred in two patients, both with LVI, despite receiving radioactive iodine and radiotherapy. The largest tumor (6 cm) did not show lymph node metastasis, while smaller tumors (2.2 cm, 2.3 cm) were metastatic. Higher mitotic rate showed necrosis and lymph nodal metastasis. Neither BRAF nor p53 positivity correlated with thyroglobulin levels.

Conclusion: HSPTC exhibits aggressive behavior, particularly in cases with LVI, high mitotic activity and necrosis. BRAF and p53 mutations are common and cause aggressiveness. Early and aggressive management are essential to improve outcomes.