Circulating Tumor Cells in Patients With Locally Advanced Rectal Cancer

This study looks at the level of circulating tumor elements (cancer cells or DNA pieces floating in the blood) and how it may be related to how the tumor responds to standard treatment in patients with rectal cancer that has spread to nearby tissue or lymph nodes (locally advanced). Researchers will also compare the level and genetic characteristics of circulating tumor elements between individuals with rectal cancer and healthy individuals to understand how they may change over time. Information from this study may help researchers better understand rectal cancer.