Abstract 3166: Impact of cancer associated fibroblast phenotypes on the infiltration of t-lymphocytes in early age onset colorectal cancer

Background: Incidences of early age onset colorectal cancer (CRC) (those diagnosed before age 50) have been increasing by 2% every year since the 1990s, with the rate expecting to double by 2030. Although there has been some research done on differences in mutational profiles between patients diagnosed before and after age 50, little research has been done to understand the immune and stromal environments of early age onset (EAO) CRC. As identified by previous literature, there are two distinct phenotypes of cancer associated fibroblasts (CAFs): myofibroblastic (myCAFs) and non-myofibroblastic (non-myCAFs). Here, we evaluate both CAF environments as well as immune infiltrating cells in context of EAO CRC. Methods: A total of 153 CRC patient samples were obtained with matching adjacent normal tissue. Of these, 60 patients had EAO CRC. Tissue slides were stained via immunohistochemistry (IHC) for the CAF subtype markers αSMA, FAP, PDPN, and MMP2, by Masson's Trichrome for collagen, and then quantified on an intensity scale from 0-3. MyCAF and non-myCAF scores were calculated by averaging the scores of αSMA and collagen, or FAP, PDPN, and MMP2, respectively. Once these scores were determined, they were split into low (average score <2) and high (average score ≥2) groups. CD4 and CD8 IHC stains were quantified as the number of tumor infiltrating lymphocytes (TILs) per high power field (HPF) in the epithelial compartment. Results: Cancers with a low myCAF and non-myCAF score display the highest average number of CD4+ (10.6) and CD8+ (10.3) TILs across both age groups. Furthermore, cancers with both myCAF and non-myCAF high scores had reduced average CD4+ and CD8+ TILs when compared to both CAF scores being low (p value: 0.018 for CD8+ TILs, <0.001 for CD4+ TILs). Also, cancers that show myCAF high and non-myCAF low scores show the overall lowest average CD8+ TILs. Comparing the age groups directly, there are significantly higher CD4+ TILs in the 50+ age group in all CAF phenotypes except non-myCAF high (p-values 0.01 myCAF low, 0.05 myCAF high, 0.007 non-myCAF low, 0.36 non-myCAF high). However, for CD8+ TILs, the EAO CRC group trends towards higher CD8+ TILs in the myCAF high (3.7 vs 2.1) and non-myCAF high cancers (5.7 vs 3.3), but lower CD8+ TILs in myCAF low (6.8 vs 10.5) and non-myCAF low cancers (4.0 vs 8.4) when compared to the 50+ age group. Conclusions: Here we demonstrate that there are differences in the stromal and immune microenvironments between both age groups of CRC. We indicate that increased myCAF and non-myCAF scores are associated with T cell exclusion. However, the extent of T cell exclusion is different in EAO CRC compared to patients diagnosed after age 50. The reasoning for the difference in T-cell exclusion remains unknown and this implicates the importance for further research into the stromal and immune microenvironments of EAO CRC. Citation Format: Anna Lippert, Katherine A. Johnson, Philip B. Emmerich, Cheri A. Pasch, Linda Clipson, Kristina A. Matkowskyi, Wei Zhang, Dustin A. Deming. Impact of cancer associated fibroblast phenotypes on the infiltration of t-lymphocytes in early age onset colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3166.