Low Stromal CD11c Expression Indicates a Poor Prognosis in Rectal Cancer Patients.

INTRODUCTION: The immune landscape of the tumor microenvironment significantly influences the development and prognosis of colorectal cancer (CRC). High intratumoral and stromal expressions of CD3+ and CD8+ T-lymphocytes have been associated with a better prognosis in CRC patients. However, the prognostic role of antigen-presenting cells, such as dendritic cells and macrophages, has less attention. METHODS: In this study, we assessed the impact of CD11c expression and the disease-specific survival (DSS) in CRC patients. Thus, we evaluated the CD11c expression on tissue microarray samples via immunohistochemistry from 516 patients who underwent surgery at Helsinki University Hospital between 2000 and 2005. Samples were categorized as low expression (<5% positive stromal area) and high expression (≥5% positive). Colon and rectal cancer patients were analyzed separately using Cox regression for survival analysis. RESULTS: A lower CD11c expression associated with a worse DSS among rectal cancer patients (p < 0.001) and right-sided colon cancer patients (p = 0.03), but not among left-sided colon cancer patients (p = 0.41). Among rectal cancer patients, results remained consistent regardless of whether the patient received preoperative radiation (p < 0.003 and p = 0.03, respectively). In the multivariable analysis after adjusting for age, sex, stage, grade, and a mismatch repair status, a lower CD11c expression remained an independent prognostic factor among rectal cancer patients (p = 0.009), but not among colon cancer patients (p = 0.15). These results suggest that stromal CD11c expression captures the distinct immunological characteristics of rectal cancer compared to colon cancer. CONCLUSIONS: We conclude that CD11c could serve as a prognostic marker for rectal cancer patients. However, the immunological mechanisms differentiating colon and rectal cancers warrant further research.