The Bethesda System Revisited: Malignancy Risk Estimation and NIFTP Impact in a Large Cohort From Northern India

Area of Science:

• Endocrinology
• Cytopathology
• Oncology

Background:

• Thyroid nodules are frequently encountered in clinical practice.
• Fine-needle aspiration cytology (FNAC) is the primary diagnostic tool for assessing malignancy risk.
• The Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) standardizes thyroid nodule interpretation and management.

Purpose of the Study:

• To evaluate the distribution of TBSRTC categories in thyroid nodules.
• To determine the risk of neoplasia (RON) and risk of malignancy (ROM) for each TBSRTC category.
• To assess the impact of reclassifying non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) on ROM.

Main Methods:

• Retrospective review of 2578 thyroid FNAC cases from 2016-2024.
• Classification of cytological diagnoses using TBSRTC (2017 and 2023 versions).
• Histopathological correlation in 1043 cases (40.5%) to calculate RON and ROM, with ROM assessed before and after NIFTP exclusion.

Main Results:

• Benign and Malignant categories comprised the majority of cases (73.2% and 7.2%, respectively).
• ROM demonstrated a progressive increase across TBSRTC categories, ranging from 3.7%-9.9% (Benign) to 58.6%-100% (Malignant).
• Excluding NIFTP significantly reduced ROM in indeterminate categories: AUS (43.2% to 31.8%), FN (40.2% to 28.4%), and SM (52.4% to 42.9%).

Conclusions:

• TBSRTC provides reliable risk stratification for thyroid nodules.
• Reclassification of NIFTP substantially alters ROM for indeterminate categories.
• Accurate cytologic-histologic correlation and regional validation are crucial for optimizing thyroid nodule management.