Abstract 2734: Impact of the mutation profile and versican status on lymphocyte infiltration in early age onset colorectal cancer
Authors: Johnson Katherine A. , Emmerich Philip B. , Lippert Anna L. , Pasch Cheri A. , Clipson Linda , Zhang Wei , Matkowskyj Kristina A. , Deming Dustin A. 
Published: July 2021

Abstract
Background: The incidence of colorectal cancer (CRC) in those of pre-screening age continues to rise. A deeper understanding of the differences in tumor biology in early age onset (EAO) cancers is needed. Differences in the tumor microenvironment have been understudied in this setting. We previously have identified versican (VCAN), a large matrix proteoglycan, as an important factor in lymphocyte exclusion in CRC. Here we explore the impact of the mutation profile and VCAN status on the infiltration of CD8+ and CD4+ lymphocytes in EAO CRC.
Methods: Cancer tissues from 153 patients with CRC were stained via immunohistochemistry for CD4, CD8, and VCAN. CD4 and CD8 stains were quantified by number of positive-staining tumor-infiltrating lymphocytes per high powered field (TILs/HPF). VCAN stains were quantified on an intensity scale from 0-3+. 121 of these patients had tissue that was sequenced using the Qiagen Comprehensive Cancer targeted sequencing panel, and variations were called using Strelka. Patients were split by age into early-onset (EAO; age at diagnosis &lt;50) and later-onset (LAO; age at diagnosis 50 or later).
Results: Mutations in BRAF and APC were significantly more common in LAO cancers (p&lt;0.05 for both). TP53 mutations were correlated with significantly lower CD4+ and CD8+ TILs/HPF in the LAO cohort (12.6 CD4+ TILs/HPF for TP53-wild type [WT] vs 3.5 for TP53-mutant, p&lt;0.001; 10.0 CD8+ TILs/HPF for WT vs 3.2 for mutant, p&lt;0.01), but trended opposite, though not statistically significant, in the EAO group (2.4 vs 5.9 CD4+ TILs/HPF; 3.0 vs 5.9 CD8+ TILs/HPF). PIK3CA mutations were correlated with an increase in CD8+ TILs in the LAO cohort (5.3 vs 11.9 CD8+ TILs/HPF; p&lt;0.05) but a decrease in CD4+ TILs in the EAO cohort (4.9 vs 0.8 CD4+ TILs/HPF; p&lt;0.05). TP53-WT tumors are disproportionately low in VCAN in the LAO cohort (p&lt;0.01). Differences in VCAN accumulation could account for the changes in CD8+ and CD4+ T lymphocyte infiltration across the age cohorts and TP53 mutation status.
Conclusions: The impacts of TP53 and PIK3CA mutations on immune infiltration in CRC differ in EAO compared to later onset cancers, indicating that the processes controlling immune infiltration vary between age cohorts. Such differences in immune infiltration may be linked to changes in microenvironmental factors such as VCAN. These data warrant further investigation into the relationship between tumor microenvironment and mutation profiles in EAO CRC.
Citation Format: Katherine A. Johnson, Philip B. Emmerich, Anna L. Lippert, Cheri A. Pasch, Linda Clipson, Wei Zhang, Kristina A. Matkowskyj, Dustin A. Deming. Impact of the mutation profile and versican status on lymphocyte infiltration 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 2734.