The prospective study will focus on patients undergoing multimodal treatment for rectal cancer. The main objective of the study will be to monitor changes in circulating tumor cells (CTCs) in the peripheral blood of patients during multimodal treatment. For each patient enrolled in the study, peripheral blood samples will be collected at specified time intervals to determine the presence and quantity of CTCs. The CTCs levels will be compared among rectal cancer patients with neoadjuvant chemoradiotherapy and without neoadjuvant chemotherapy.