Activated immune infiltrates expand opportunities for targeted therapy in p53-abnormal endometrial carcinoma

Abstract

Tumor protein p53 mutated/abnormal (p53abn) endometrial carcinomas account for over 50% of deaths but comprise only 15% of all endometrial carcinomas. Most patients show limited response to standard-of-care chemotherapy with or without radiotherapy, and only a minority of cases are amenable to targeted therapies like poly-ADP ribose polymerase (PARP) inhibitors and HER2-directed therapies. Recent immunotherapy clinical trials have demonstrated remarkable efficacy, not only in mismatch repair deficient (MMRd) tumors but also in a subset of mismatch repair-proficient (MMRp) tumors. However, the immune microenvironment and its relationship to other therapeutic targets in MMRp endometrial carcinoma remains poorly understood. Here, we characterize the immune microenvironment of p53abn endometrial carcinoma, the most clinically aggressive subtype of MMRp endometrial carcinoma, and correlate antitumor immune signatures with other targetable alterations. We accrued 256 treatment-naïve p53abn endometrial carcinomas and systemically profiled T-cell, B-cell, myeloid, and tumor-cell populations with multiplex immunofluorescence to assess the tissue localization and functional status of immune cells. Shallow whole-genome sequencing was performed on a subset of 126 cases. Patterns of immune infiltration were compared to survival outcomes and mutational signatures. Mixture modeling divided p53abn endometrial carcinoma into tumor-infiltrating lymphocyte (TIL)-rich and TIL-poor subsets. Over 50% of tumors were TIL-rich. TIL-rich cases overexpressed targetable immune evasion molecules and were associated with longer overall and disease-specific survival in multivariate analysis. This effect was particularly pronounced in advanced stage disease and in patients who did not receive adjuvant chemotherapy. TIL did not associate with homologous recombination deficient mutational signatures or HER2 amplification. Our findings demonstrate a biological rationale for immunotherapy in a substantial subset of patients with p53abn endometrial cancer and may help inform combination therapies with immune checkpoint inhibition, PARP inhibitors, and anti-HER2 agents. © 2025 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Keywords: HER2; PARP inhibitors; endometrial cancer; immunotherapy; p53abn; tumor microenvironment; tumor‐infiltrating lymphocytes.

Figure 1

Graphical overview of clinicopathologic parameters and data types for each sample, showing relationships between different parameters. Missing values are colored white. Grade 3 includes histotypes defined as high grade. Myo, depth of myometrial invasion; LVI, lymphovascular invasion.

Figure 2

Derivation of TIL‐rich and TIL‐poor groups. (A) Representative multiplex immunofluorescence image of B/T cell panel. Representative segmentation of tumor (red), stromal (green), and glass/necrosis (blue) are shown in top left panel. Cytokeratin (white) and DAPI (blue) are shown in each image along with a single immune marker as annotated. (B) Heatmap of log‐transformed epithelial and stromal TIL densities for each sample. Results of hierarchical clustering by sample (top dendrogram) are split by TIL cluster.

Figure 3

Univariate Kaplan–Meier survival curves and log‐rank p values of overall survival (OS) and TIL cluster. (A) All tumors in cohort with known stage and chemotherapy status. (B–E) Tumors grouped by stage. (F and G) Univariate Kaplan–Meier survival curves and log‐rank p values of disease‐specific survival (DSS) and TIL cluster grouped by adjuvant chemotherapy status. (H) Distribution of epithelial CD8⁺ TIL densities for each histotype.

Figure 4

Expression of immune checkpoint molecules in TIL‐rich versus TIL‐poor p53abn endometrial cancer. (A) Relative proportions of CD8⁺ TIL that express PD‐1 for each TIL cluster. (B) Relative abundances of CD8⁺ T cell versus T regulatory cells (CD8/Treg) in TIL‐rich and TIL‐poor tumors. (C) Densities of CD68⁺ macrophages expressing PD‐L1, IDO1, both, or neither, in TIL‐rich versus TIL‐poor cases. (D) Proportions of tumor cells that express PD‐L1, IDO1, or both in TIL‐rich versus TIL‐poor cases. P values (Mann–Whitney U test) corrected for multiple comparisons within each heading are shown. Boxplot bars, boxes, and whiskers show median, first (Q1), and third (Q3) quartiles and Q1–1.5*IQR (interquartile range) and Q3 + 1.5*IQR, respectively. Mann–Whitney U test p values shown with multiple hypothesis testing correction by Holm method.

Figure 5

(A) Overview of relationship between TIL cluster, HRD‐associated CN signature (VS5), and HER2 status. Tumors where VS5 was the dominant CN signature are designated positive. HER2 positivity is defined by an IHC score of 3⁺ or amplification or high‐level amplification by whole‐genome sequencing. (B) Relative proportion (exposure) of HRD‐associated copy number signature in TIL‐poor and TIL‐rich samples. Boxplot bars, boxes, and whiskers show median, first (Q1), and third (Q3) quartiles and Q1–1.5*IQR (interquartile range) and Q3 + 1.5*IQR, respectively. (C and D) Number of TIL‐rich samples (orange) in comparison to TIL‐poor samples (blue) by (C) HER2 IHC score according to College of American Pathologist recommendations for endometrial carcinoma [74] and (D) HER2 CN status. HLAmp, high‐level amplification.