Effect of neoadjuvant chemoradiation on tumor-infiltrating/associated lymphocytes in locally advanced rectal cancers

Background: Lymphocytes and natural killer cells (NK) appear to be important in colorectal cancer. Their role in chemoradiotherapy for rectal cancers is unclear. We evaluated T-lymphocytes (CD3), sub-groups CD4 and CD8, and NK cells (CD56+CD57) in normal and rectal tumor tissues pre- and post-chemoradiotherapy, and investigated their relationship to tumor regression grade, disease-free survival and pathological stage. Materials and Methods: Tissue microarrays from colonoscopic biopsies, resection specimens and normal tissues, from 52 patients, were immunostained. Results: NK cell counts were significantly lower in tumor samples compared to normal tissues (p=0.007). T-lymphocyte counts were higher in post-treatment compared to pre-treatment samples (p=0.025), specifically in the CD8 subgroup after long-course treatment. The results suggested an association between post-treatment CD8 and NK cell counts with higher tumor regression. No associations were found with regard to stage or disease-free survival. Conclusion: NK cell counts were significantly reduced in rectal cancers compared to normal tissues, while total T-lymphocyte counts increased post-chemoradiotherapy. Both appeared important in tumor regression.