Cytologic diagnostic approach to poorly differentiated thyroid carcinoma: a single-institution study

Area of Science:

• Cytopathology
• Oncology
• Endocrinology

Background:

• Fine-needle aspiration cytology (FNAC) is a standard preoperative tool for thyroid nodules.
• Cytologic diagnostic criteria for poorly differentiated thyroid carcinoma (PDTC) are not standardized, unlike its histological criteria.
• PDTC are rare tumors, and review articles on their cytologic diagnosis are scarce.

Purpose of the Study:

• To investigate the cytomorphological features of PDTC.
• To identify distinguishing features between PDTC, differentiated thyroid carcinoma (DTC), and medullary thyroid carcinoma (MTC).

Main Methods:

• Retrospective analysis of 44 PDTC FNAC smears from a single tertiary cancer institute (2009-2013).
• Evaluation of 21 cytomorphologic features on Papanicolaou and Giemsa stained smears.
• Limited availability of immunocytochemistry (6 cases).

Main Results:

• Common features included hypercellularity (84.1%), insular pattern (79.5%), small cell size (93.2%), high nuclear-cytoplasmic ratio (93.2%), granular chromatin (95.45%), nuclear overlapping (88.64%), and mild pleomorphism (86.36%).
• Less frequent features were grooves/inclusions (22.7%), binucleation (9.1%), abrupt nucleomegaly (34.1%), apoptosis (45%), mitosis (25%), necrosis (34.1%), and colloid (22.7%).

Conclusions:

• A high index of suspicion is crucial for upfront PDTC diagnosis on FNAC.
• While PDTC, DTC, and MTC share overlapping features, distinguishing characteristics exist.
• Standardization of cytologic diagnostic criteria for PDTC through collaborative efforts is needed for prompt diagnosis and multimodality treatment planning.