Identification and prognostic value of non-hotspot POLE exonuclease domain mutations in endometrial cancer

BACKGROUND: Endometrial cancer with somatic POLE exonuclease domain mutations (EDMs) has a highly favorable prognosis; however, the clinical implications of non-hotspot EDMs in POLE remain unclear. MATERIALS AND METHODS: In 793 patients with endometrial cancer enrolled at the National Cancer Center and Juntendo University Hospitals, 25 prespecified variants were screened using the Luminex assay. Whole-exome sequencing (WES) was carried out to evaluate 54 patients with hotspot and non-hotspot EDMs. In patients with endometrial cancer (n = 4864) registered in Genomics Evidence Neoplasia Information Exchange (GENIE), those harboring hotspot EDMs were matched with randomly sampled patients without EDMs, and a polymerase epsilon (POLE) score for gene panel testing was developed. RESULTS: In our cohort, POLE-EDMs, including hotspot (n = 91) and non-hotspot (n = 12) EDMs, were identified in 103 (12.9%) of 793 patients. The prevalence of grade 3 and advanced-stage endometrial cancer was higher in patients with non-hotspot EDMs than in those with hotspot EDMs. WES analysis of 54 patients revealed no significant differences in genomic mutations between the groups, and four non-hotspot EDMs were identified. A POLE-specific mutational signature was observed in tumors with EDM. In addition, the POLE score criteria were developed based on hotspot EDMs using the GENIE cohort, achieving a detection sensitivity of 0.94. Using the established POLE score, we identified nine non-hotspot EDMs. CONCLUSIONS: We identified 13 novel candidate non-hotspot EDMs using a newly established POLE score for gene panels and demonstrated an association between non-hotspot EDMs and favorable prognosis. The identification of additional non-hotspot EDMs will facilitate precise molecular classification of endometrial cancer.