Abstract 6478: Relapse prediction of stage III MSS colon cancer by certain cell subtype distribution characteristics in tumor and tumor invasive margin

Colorectal cancer (CRC) is a frequent gastrointestinal malignancy with high rates of morbidity and mortality. Previous studies have shown a significant correlation (p<0.001) between immune score and recurrence time, overall survival, and disease-free survival in subgroups of microsatellite stability (MSS) patients with stage II colon cancer. Current study reviewed 17 stage III MSS CRC patient archived FFPE samples including 11 relapse and 6 no-relapse, to investigate their immune cell features and the correlation to relapse after chemotherapy. IHC control, multiplex immunofluorescence (mIF) panel control and the followed mIF staining were conducted using PN 6-Plex Detection Kit (PhenoVision Bio Co., Itd) targeted CD68, CD3, CD20, panCK, PD-L1 and PD-1. The 17 staining slides were scanned, tumor areas were lined out by pathologist based on H&E staining from the serial section of each sample. Non-tumor region, tumor invasive margin (IM), which was defined as 360μm within and outside of tumor boundary i.e. total 720μm, tumor islands and stromal areas were analyzed using PhenoVision mIF AI analysis system trained from Oncotopix Discovery system (Visiopharm). Statistical analysis exhibited significant correlation of MSS mIF results to relapse rate based on binary logistic regression (p<0.05). Positive cell percentage and positive cell densities were both analyzed in 17 samples. When focused in tumor region, there were significant variated PD-1 negative/CD20 positive cells in tumor stromal region between relapse and non-relapse group (6.64% in non-relapse vs. 2.58%in relapse, p=0.026). Significant differences were observed in PD-L1/CD3 co-positive cell subtype (p=0.01) between relapse and non-relapse groups. Further focus on tumor and IM region, we observed significant more PD-1 negative/CD20 positive cell subtype in IM region compared to tumor area in relapse groups (0.68% tumor vs. 2.21% IM, p=0.0483). Similar trend of less in tumor and more in IM region with CD3 positive and PD-1 negative/CD3 positive cell subtypes was observed in non-relapse group, with p=0.05. Current study indicated that tumor microenvironment carried significant amount variations of cell subtypes between relapse and non-relapse groups. Although there were certain amount of PD-1 negative/CD20 positive cell subtype in relapse group, most located in IM region. The cell distribution feature may be utilized for prognosis prediction of MSS stage III CRCs after chemotherapy to guide patients' health monitoring plans after treatment. Moreover, therapies improve PD-1 negative/CD20 positive and such immune cell subtypes infiltrated into tumor region may improve patient prognosis which need more studies in the field. Citation Format: Hanqing Hu, Hongzhe Sun, Xia Liu, Shuo Han, Lin Zhu, Miao Wang, Zhifu Zhang, Na Li, Guiyu Wang. Relapse prediction of stage III MSS colon cancer by certain cell subtype distribution characteristics in tumor and tumor invasive margin [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6478.