LAUSR

Background: Despite heightened interest in early-onset CRC, little is known about the tumor molecular, immune, and microbial characteristics of early-onset CRC. It is also unclear whether CRCs diagnosed at or shortly after age 50 are similar to early-onset CRC. We hypothesized that tumor molecular, immune, and microbial characteristics in CRC tissue might show differential heterogeneity patterns between three age groups (<50 "early-onset", 50-54 "intermediate-onset", ≥55 "later-onset"). Methods: We examined 3,395 CRC cases with available tissue data, including 660 early-onset and 243 intermediate-onset cases in the Nurses' Health Study, Health Professionals Follow-up Study, and Ontario Familial Colon Cancer Registry. We profiled the in situ T-cell landscape of 959 cases using digital imaging, machine learning, and a customized 9-plex multiplexed immunofluoresence panel with antibodies directed against CD3, CD4, CD8, CD45RA, CD45RO, FOXP3, and MKI67 (Ki-67). Using chi-squared test or Spearman’s correlation test, we assessed differences in tumor characteristics including microsatellite instability, CpG island methylator phenotype (CIMP), KRAS, and BRAF mutations, LINE-1 methylation levels, pks+ E. coli and Fusobacterium nucleatum positivity, histopathologic lymphocytic reaction, and T-cell densities between early-onset, intermediate-onset, and later-onset cases. Results: Compared to later-onset CRC (21%), early-onset (4.8%) and intermediate-onset CRCs (5.1%) exhibited a lower prevalence of CIMP-high status (P<0.001). The mean tumor LINE-1 methylation level increased with increasing age [59 (SD, 12) in early-onset, 61 (SD, 10) in intermediate-onset, and 64 (SD, 9.8) in later-onset CRC (P<0.001)]. Early-onset CRC (4.1%) had fewer BRAF mutations than intermediate-onset (10.4%) and later-onset CRC (15%) (P<0.001). Compared to later-onset CRC, early-onset CRC tended to show lower levels of tumor-infiltrating lymphocytes (P=0.013), and intratumoral periglandular reaction (P=0.025). Compared to later-onset CRC, early-onset CRC had a lower density of memory (both CD4+ and CD8+) T-cells (median 21 vs. 48 cells/mm2; P=0.002) and a higher density of MKI67+ immune cells (median 50 vs. 19 cells/mm2; P=0.003) in tumor epithelial areas but not in the surrounding stroma. No significant differences in other tested characteristics were identified. Conclusions: Compared to later-onset CRC, early-onset and intermediate-onset CRCs tended to have aggressive tumor phenotypes such as LINE-1 hypomethylation, lower lymphocytic immune reaction, and a higher density of MKI67+ immune cells. These findings highlight the importance of the tumor microenvironment in the etiology of early-onset and intermediate-onset CRCs. Citation Format: Tomotaka Ugai, Yasutoshi Takashima, Andressa Dias Costa, Daniel Buchanan, Jeroen Huyghe, Li Hsu, Conghui Qu, Claire Thomas, Steve Gallinger, Robert Grant, Ulrike Peters, Amanda I. Phipps, Jonathan Nowak, Shuji Ogino. Molecular, immune, and microbial profiles of early-onset, intermediate-onset, and later-onset CRCs. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5760.