Cytopathological features associated with POLE mutation in endometrial cancer

For patients with endometrial cancer, the POLE (polymerase epsilon) mutation (POLEmut)-subtype, one of four molecular-analysis-based categories in the Cancer Genome Atlas (TCGA), has the best prognosis. The following histological characteristics are typically observed in endometroid carcinoma cases with the POLEmut-subtype: (1) the presence of tumour giant cells, (2) numerous tumour-infiltrating lymphocytes (TILs) and/or peri-tumoral lymphocytes, and (3) a high grade. However, in the context of cytology, the morphological characteristics of this subtype remain unknown.

DNA extracted from formalin-fixed paraffin-embedded (FFPE) tissues was subjected to next-generation sequencing analysis and categorised according to the TCGA classifications. Genomic mutation, tumour mutation burden (TMB), and microsatellite instability were also assessed. Cytological specimens of resected uteri obtained using the Papanicolaou method were histologically separated into three types.

Seven out of 112 patients (6%) with endometrial cancer were diagnosed with the POLEmut-subtype between January 2019 and August 2021. Tumour giant cells were observed in three cases (43%) on histology and cytology. TIL and/or peritumoral lymphocytes with inflammatory cells were detected in five cases (71%) on histology and three cases (43%) on cytology. Cases in which these three characteristics were observed on both cytology and histology may have belonged to the POLEmut-subtype. There were no cases in which these characteristics were absent on histology but present on cytology. TMB tended to be higher in cases when the three characteristics were observed in both cytological and histological findings.

Preoperative endometrial cytology highlighted the characteristics of the POLEmut-subtype in the histological analysis of resected uterine specimens and has the potential to play an important role in treatment decisions.