Endometrial Liquid‐Based Cytology Specimens Preserve High Genome Quality for Molecular Classification After Long‐Term Storage

Background Molecular classification of endometrial cancer is useful for predicting prognosis. Genomic examinations are performed using formalin‐fixed paraffin‐embedded (FFPE) tissues; however, we previously reported that liquid‐based cytology (LBC) specimens can be used for next‐generation sequencing (NGS). In this study, we evaluated long‐term storage effects of LBC specimens on NGS‐based genomic profiling, including gene mutations, tumor mutation burden (TMB), and microsatellite instability (MSI). Methods Four LBC fixatives (CellPrep, ThinPrep, CytoRich Red, and SurePath) were used to prepare NGS samples from cultured endometrioid carcinoma HEK‐251 cells. Twelve endometrial LBC specimens from patients with endometrioid carcinoma were fixed with CytoRich Red. The TMB, MSI, and gene mutations were analyzed after 1 week, 6 months, and 12 months of storage in cultured HEK‐251 cells. Paired LBC and FFPE specimens of endometrioid carcinoma stored for 15–45 months were subjected to NGS‐based analysis, and their molecular profiles were compared to those at the initial diagnosis. Results The TMB and MSI did not differ during the storage periods for any of the LBC fixatives in the cultured cells; in addition to gene mutations, they were comparable between the initial and second analyses of the clinical FFPE and LBC specimens. There were no changes in the integrative diagnosis of the endometrioid carcinoma subtype classification. Conclusion LBC specimens, which preserved high‐quality genomes for molecular classification after long‐term storage, may be an alternative source of genomic examination for the integrative diagnosis of endometrial cancer.