Thyroid cytology smear slides: An untapped resource for ThyroSeq testing

Area of Science:

• Oncology
• Genetics
• Pathology

Background:

• Molecular testing of thyroid nodules with indeterminate fine-needle aspiration (FNA) cytology guides patient management.
• This testing is typically performed on fresh FNA samples.

Purpose of the Study:

• To evaluate the performance of the ThyroSeq test using cytology smear slides.
• To compare ThyroSeq v3 Genomic Classifier (GC) results from cytology smears and fresh FNA samples.

Main Methods:

• Air-dried Diff-Quik (DQ)-stained and alcohol-fixed Papanicolaou (Pap)-stained smears were analyzed.
• Cellularity and mutation detection sensitivity were determined.
• ThyroSeq v3 GC results from smears were compared to fresh FNA samples from the same nodules.

Main Results:

• 25 out of 31 (81%) cytology smears were adequate for ThyroSeq analysis, with a higher success rate for Pap-stained smears (100%) compared to DQ-stained smears (65%).
• The overall accuracy for detecting molecular alterations was 98%, with high concordance for mutations, gene expression, fusions, and copy number alterations.
• Adequate cellularity required 200-300 cells across 1-3 slides; ThyroSeq detected mutations down to 1-5% allele frequency.

Conclusions:

• Thyroid FNA cytology smears with adequate cellularity can be used for ThyroSeq GC testing in approximately 80% of cases.
• Smear testing achieved 94%-100% accuracy in detecting genetic alterations compared to fresh FNA samples.
• Cytology smears are validated as an alternative for ThyroSeq testing in patients with indeterminate thyroid cytology.