AB066. SOH22ABS061. Mucinous rectal cancer is associated with an immune rich tumour microenvironment and enhanced expression of PD-1
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AB066. SOH22ABS061. Mucinous rectal cancer is associated with an immune rich tumour microenvironment and enhanced expression of PD-1

William Duggan1, Emer O’Connell1, Batuhan Kisakol2, Jochen H. Prehn1, John Burke2, Deborah McNamara1

1Department of Colorectal Surgery, Beaumont Hospital, Dublin, Ireland; 2Department of Physiology and Medical Physics, Royal College of Surgeons, Dublin, Ireland

Background: Mucinous adenocarcinoma of the rectum is a molecularly distinct subtype of rectal cancer (RC), associated with a poor response to chemoradiotherapy. Immune checkpoint inhibitors are anti-cancer therapeutics that can overcome tumour mediated immune suppression in solid-organ tumours. Previous work from our group, found significant correlation between mucinous RC and elevated expression of various immune checkpoints. The aim of the current study was to validate our previous findings within our own clinical cohort, and further characterise the immune landscape of mucinous RC.

Methods: Multiplexed immunofluorescence staining of tumour micro-arrays were undertaken using Cell DIVE™. This involves multiple rounds of antibody staining performed on the same tissue sections with mild dye oxidation between successive rounds of staining and imaging. Staining intensity was measured within each tumour core and expressed as mean staining intensity at the patient level.

Results: Our cohort included 15 cases of mucinous and 43 cases of non-mucinous RC. Of the mucinous cohort, 53.3% received neoadjuvant chemoradiotherapy and 14.3% were found to be microsatellite instability-high. The mucinous cohort demonstrated enhanced expression of the immune checkpoint PD-1 (P=0.02), as well as regulatory T-cells (P=0.009). Cytotoxic T-cells were found in greater abundance in the tumour microenvironment of mucinous tumours (P=0.02), though tumour infiltration was only marginally higher in this group (P=0.72).

Conclusions: We have found mucinous RC to be associated with an immune rich tumour microenvironment. PD-1 expression is enhanced in this cohort and correlates positively with a reduction in cytotoxic T-cell tumour infiltration. Our findings strongly support a possible future role for immune checkpoint inhibition in mucinous RC.

Keywords: Cell DIVE; immune checkpoint inhibition; immunotherapy; mucinous; rectal cancer (RC)

Acknowledgments

Funding: None.

Footnote

Conflicts of Interest: The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

doi: 10.21037/map-22-ab066
Cite this abstract as: Duggan W, O’Connell E, Kisakol B, Prehn JH, Burke J, McNamara D. AB066. SOH22ABS061. Mucinous rectal cancer is associated with an immune rich tumour microenvironment and enhanced expression of PD-1. Mesentery Peritoneum 2022;6:AB066.

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