Polymerase ε (POLE) ultra-mutation in uterine tumors correlates with T lymphocyte infiltration and increased resistance to platinum-based chemotherapy in vitro

Abstract

Objective Up to 12 % of all endometrial-carcinomas (EC) harbor DNA-polymerase-ε-(POLE) mutations. It is currently unknown whether the favorable prognosis of POLE-mutated EC is derived from their low metastatic capability, extraordinary number of somatic mutations thus imparting immunogenicity, or a high sensitivity to chemotherapy. Methods Polymerase-chain-reaction-amplification and Sanger-sequencing were used to test for POLE exonuclease-domain-mutations (exons 9–14) 131 EC. Infiltration of CD4+ and CD8+ T-lymphocytes (TIL) and PD-1-expression in POLE-mutated vs POLE wild-type EC was studied by immunohistochemistry (IHC) and the correlations between survival and molecular features were investigated. Finally, primary POLE-mutated and POLE-wild-type EC cell lines were established and compared in-vitro for their sensitivity to chemotherapy. Results Eleven POLE-mutated EC (8.5%) were identified. POLE-mutated tumors were associated with improved progression-free-survival (P<0.05) and displayed increased numbers of CD4+ (44.5 vs 21.8; P = .001) and CD8+ (32.8 vs 13.5; P < .001) TILs when compared to wild-type POLE EC. PD-1 receptor was overexpressed in TILs from POLE-mutated vs wild-type-tumors (81% vs 28%; P < .001). Primary POLE tumor cell lines were significantly more resistant to platinum-chemotherapy in-vitro when compared to POLE-wild-type tumors (P < 0.004). Conclusions POLE ultra-mutated EC are heavily infiltrated with CD4+/CD8+ TIL, overexpress PD-1 immune-check-point (i.e., features consistent with chronic antigen-exposure), and have a better prognosis when compared to other molecular subtypes of EC patients. POLE-mutated tumor-cell lines are resistant to platinum-chemotherapy in-vitro suggesting that the better prognosis of POLE-patients is not secondary to a higher sensitivity to chemotherapy but likely linked to enhanced immunogenicity.

Molecular Subtype Not Immune Response Drives Outcomes in Endometrial Carcinoma

“…There is increasing appreciation of the importance of the tumor microenvironment in defining outcomes and therapeutic opportunities in cancer. In particular, TILs have been shown to be both prognostic and predictive in that their presence is generally associated with improved outcomes and favorable response to conventional chemotherapies and immune-targeting agents (1)(2)(3)(4)(45)(46)(47)(48)(49). We investigated the relationships between immune response, molecular subtype, and patient survival in endometrial cancer.…”

“…Thus, molecular subtype, not immune response, was the most significant prognostic factor in this series, suggesting that the molecular/genomic features of tumors influence outcome through mechanisms apart from the immune response. Immune markers have been assessed in endometrial cancer in both the pre-(2, 50) and post-TCGA eras (12,30,31,46,51). The latter have primarily focused on the newly recognized POLE ultramutated and MSI/MMRd-hypermutated subtypes.…”

Interpretation of somatic POLE mutations in endometrial carcinoma

“…A review of the literature was undertaken, to the end of 2018, to identify ECs in which POLE had been sequenced and the mutations published [6,7,[9][10][11][12][13][14][15][17][18][19][20][21][22]24,25]. All literature contributing entries into the COSMIC database (POLE + endometrium) were reviewed; in addition, searches in PubMed and Web of Science were undertaken with the keywords 'POLE + Endometrial + Carcinoma' and 'POLE + Endometrial + Cancer', noting that 'POLε' is interpreted as 'POLE' in these resources.…”

“…'POLE ultramutated' EC (POLEmut EC) has therefore been proposed as a distinct clinical entity that can be diagnosed in the presence of a pathogenic POLE exonuclease domain mutation (EDM) [8]. For the five most common POLE mutations (P286R, V411L, S297F, A456P, and S459F), pathogenicity (in this sense meaning causal for tumour ultramutation) has been confirmed [4][5][6][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]; however, the classification of other, less frequent POLE variants is currently challenging. This is becoming an urgent problem, as POLE sequencing for molecular EC classification is rapidly entering clinical practice.…”

“…To define the extent of the problem of ascribing pathogenicity to POLE mutations in clinical practice, we identified 296/3840 (7.7%) tumours with a somatic POLE mutation from EC cohorts other than TCGA [6,7,[9][10][11][12][13][14][15][17][18][19][20][21][22]24,25] (Table 5 and supplementary material, Table S3). Of 296 non-TCGA POLE-mutant ECs reported in the literature, 15 had mutations outside the exonuclease domain, and 254 carried mutations in the exonuclease domain previously detected in the TCGA and classified by POLE-scores as pathogenic (249 cases), of uncertain pathogenicity (four cases), or non-pathogenic (one case).…”