Rectal cancer staging is based on the TNM system. "T" refers to the primary tumor, "N" indicates whether there are lymph node metastases, and "M" indicates the presence of distant metastases. Staging is determined according to these factors. Stage II generally refers to patients with T3, N0, M0, or T4, N0, M0. What does this mean? T3 indicates that the tumor has penetrated the base layer reaching the subserosal layer, or has invaded the tissues adjacent to parts of the colon or rectum that are not covered by peritoneum, which is described as T3. T4 means that the tumor has invaded through the entire bowel wall, perforated the visceral peritoneum, and involved other organs or structures, which is called T4. N0, M0 means there are no lymph node metastases and no distant metastases, such as to the liver or lungs. Such patients are clinically staged as stage II rectal cancer.