Rectal cancer, comprised of 30% of overall colorectal cancer cohort, is one of the leading cancers of Taiwan. In patients with advanced disease, the standard of care is concurrent chemoradiotherapy (CCRT) before surgery. After CCRT, the abscopal effect, a phenomenon that localized radiation not only destroys local tumor but also inhibits the growth of tumor at the remote site, has been observed. This effect is believed to be associated with tumor immune response. In addition, other immune checkpoint molecules, such as Programmed cell death-1(PD-1), Programmed cell death ligand-1 (PD-L1), and Cytotoxic T-Lymphocyte Associated Protein 4 (CTLA-4), have been reported associated with therapeutic outcome. However, after CCRT, more than 50% of patients were still either having persistent disease or developed distant metastasis. To improve therapeutic outcome of patients with rectal cancer, this project, thus, aims at exploring the evolution of factors that may affect the abscopal effect and immune checkpoint functions in tissues and in blood before and after CCRT.

For most patients, preoperative chemoradiotherapy results in clinically tumor regression, but the degree of response varies among patients. There are approximately 40-60% of LARC patients treated with CCRT achieve some degree of pathologic response. However, there is yet an effective method before the commencement of CCRT that can predict how patients will respond to CCRT and can subsequently render better survival. Identify patents who will benefit most from CCRT is crucial not only in lowering treatment-related morbidity and sustaining local control but also to improve survival rate in LARC.

Inclusion Criteria:

• Rectal cancer patients in China Medical University Hospital (Age limit: 20 yrs and older)

Exclusion Criteria:

• Pregnancy, Disabilities

Rectal cancer patients in China Medical University Hospital (Age: 20 yrs and older)