A Review of Scheduling Strategies for Radiotherapy and Immune Checkpoint Inhibition in Locally Advanced Rectal Cancer

Colorectal cancer (CRC) is the third most common malignancy across the globe and, despite advances in treatment strategies, survival rates remain low. Rectal cancer (RC) accounts for most of these cases, and traditional management strategies for advanced disease include total neoadjuvant therapy (TNT) with chemoradiotherapy followed by curative surgery. Unfortunately, approximately 10-15% of patients have no response to treatment or have recurrence at a short interval following radiotherapy. The introduction of immunotherapy in the form of immune checkpoint blockade (ICB) in metastatic colorectal cancer has improved clinical outcomes, yet most patients with RC present with microsatellite stable disease, which lacks the immune-rich microenvironment where ICB is most effective. There is evidence that combining radiotherapy with ICB can unlock the mechanisms that drive resistance in patients; however, the sequencing of these therapies is still debated. This review offers a comprehensive overview of clinical trials and preclinical models that use radiotherapy-immunotherapy combinations in RC in an attempt to extrapolate the ideal sequencing of the two treatment modalities. The results highlight the dearth of evidence to answer the question of whether ICB should be given before, during, or after radiotherapy, yet it is suggested that improving the relevance of our preclinical models will provide a platform with higher translational value and will lead to appropriate clinical trial designs.

Spatially Resolved Transcriptomics Deconvolutes Prognostic Histological Subgroups in Patients with Colorectal Cancer and Synchronous Liver Metastases

Strong immune responses in primary colorectal cancer correspond with better patient survival following surgery compared with tumors with predominantly stromal microenvironments. However, biomarkers to identify patients with colorectal cancer liver metastases (CRLM) with good prognosis following surgery for oligometastatic disease remain elusive. The aim of this study was to determine the practical application of a simple histological assessment of immune cell infiltration and stromal content in predicting outcome following synchronous resection of primary colorectal cancer and CRLM and to interrogate the underlying functional biology that drives disease progression. Samples from patients undergoing synchronous resection of primary colorectal cancer and CRLM were evaluated in detail through histological assessment, panel genomic and bulk transcriptomic assessment, IHC, and GeoMx spatial transcriptomics (ST) analysis. High immune infiltration of metastases was associated with improved cancer-specific survival. Bulk transcriptomic analysis was confounded by stromal content, but ST demonstrated that the invasive edge of the metastases of long-term survivors was characterized by adaptive immune cell populations enriched for type II IFN signaling and MHC-class II antigen presentation. In contrast, patients with poor prognosis demonstrated increased abundance of regulatory T cells and neutrophils with enrichment of Notch and TGFβ signaling pathways at the metastatic tumor center. In summary, histological assessment can stratify outcomes in patients undergoing synchronous resection of CRLM, suggesting that it has potential as a prognostic biomarker. Furthermore, ST analysis has revealed significant intratumoral and interlesional heterogeneity and identified the underlying transcriptomic programs driving each phenotype.

SIGNIFICANCE

Spatial transcriptomics uncovers heterogeneity between patients, between matched lesions in the same patient, and within individual lesions and identifies drivers of metastatic progression in colorectal cancer with reactive and suppressed immune microenvironments.

Spatially resolved transcriptomics deconvolutes histological prognostic subgroups in patients with colorectal cancer and synchronous liver metastases

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Background: Up to 50% of patients with Colorectal Cancer (CRC) will metastasise to the liver (CRLM). KRAS-mt liver metastases particularly when co-mutated with TP53 are associated with poor prognosis. We have used the Glasgow Microenvironment Score (GMS), a histological score performed on H+E slides utilising immune and stromal components of the microenvironment to robustly stratify outcome in primary CRC. The aim of the current study was firstly to determine the utility of GMS in metastatic CRC and secondly to employ the NanostringTM GeoMx Digital Spatial Profiler (DSP), a state-of-the art analysis platform enabling spatial transcriptomic characterisation while maintaining tumour microenvironment (TME) topographical features, to interrogate the functional biology underlying the GMS. Methods: FFPE specimens from primary and metastatic lesions from 44 patients undergoing synchronous resection of CRLM underwent GMS, IHC and panel genomic assessment. Primary endpoints were recurrence-free survival (RFS) and cancer-specific survival (CSS). In addition to bulk transcriptomic assessment, 4 matched pairs from the cohort were selected for GeoMx analysis: 2 samples were GMS0 (high-immune) and 2 were GMS1 (low-immune) with an equal distribution of KRASmt and wt. After multiplex IF staining (PanCK, CD45, DAPI, αSMA), 48 regions of interest were selected and Cancer Transcriptome Atlas Transcriptomic outputs (2000 genes) were analysed using Pathway enrichment analysis with immune deconvolution of the transcriptome performed. Results: GMS0 (high-immune) was associated with improved RFS (p=0.0048) and CSS (p=0.0012) remaining an independent predictor of survival on multivariate analysis (HR 2.90, 95% C.I 1.18-7.16 P=0.021). GMS0 lesions were enriched for adaptive immune (NES=2.20 p.adj<0.0005) and IL-10 (NES=1.9 p.adj<0.0005) pathways specifically at the invasive edge. In contrast, a poor prognostic KRAS/TP53 lesion demonstrated profound immunosuppression, upregulated NOTCH signalling (NES=2.13 p.adj<0.0005) and neutrophil degranulation (NES=1.99 p.adj<0.0005). Topographical Immune-cell deconvolution demonstrated significantly higher populations of CD4 (p=0.05) and CD8 (p=0.0003) cells in GMS0 leading edges. Conclusions: We have demonstrated that spatial transcriptomic analysis using the Nanostring GeoMx tool can reveal potential novel mechanisms underlying biologically relevant histological and mutational subgroups (KRAS-mt) of CRC, providing potential therapeutic targets requiring further investigation. Future studies will apply this technology to pre and post treatment biopsy samples.