V28: Molecular Basis of Extramural Vascular Invasion (EMVI) Positive Colorectal Carcinoma

Extramural Vascular Invasion (EMVI) is a known poor prognostic factor in Colorectal Carcinoma (CRC). However, its molecular basis has not been well defined. Our aim in this study is to assess the expression of immune and molecular markers in EMVI positive Colorectal Carcinoma in order to understand their tumor microenvironment.


Methods:

Clinicopathological records of 987 patients who underwent CRC surgery at our institution (N=300 EMVI positive) were extracted from an IRB approved database. Immunohistochemistry was performed on tissue microarrays of the respective surgical pathology specimens for immune and molecular markers. Automated quantification was used for CD8, LAG3, FOXP3, CD163, HSAT II non-coding RNA repeats; & manual quantification was used for PD-L1, HLA I markers (Beta-2 Microglobin, HC10) and HLA II. Dual staining for PDL1-PU1 was also performed, and represented tumor associated macrophages.

CD8, LAG3, FOXP3, CD163, PU1, PDL1 positive macrophages were represented as cells/mm²  tissue area. HSAT II was represented as average number of copies per cell. PDL1, HLA I and II markers were expressed as percentages of tumor cells positive for these markers. Wilcoxon signed-rank test was used to compare EMVI positive and negative tumors.


Results: PDL1 was barely expressed on tumor cells throughout the entire cohort. There was significantly lower expression of CD8 (p=0.009), LAG3 (p=0.03), FOXP3 (p < 0.0001), PU1 immune cells (p=0.0004), PDL1 positive macrophages (p < 0.0001) and Beta-2 Microglobin on tumor cells (p=0.003) in the EMVI positive tumors when compared to the EMVI negative tumors. When looking at chemo naïve tumors, LAG3 (p=0.04), FOXP3 (p=0.001), PU1 immune cells (p=0.04), PDL1 positive macrophages (p=0.0001) and Beta-2 Microglobin on tumor cells (p=0.01) also had significantly lower expression in EMVI positive tumors.


Conclusions:

There is blunting of the immune response in EMVI positive tumors compared to EMVI negative tumors in CRC. Further studies are needed to better elucidate the role of immunoregulatory cells in the context of CRC.