TNM staging of colorectal cancer American Joint Committee on Cancer (AJCC)/UICC TNM staging system for colorectal cancer (7th edition) Primary tumor (T) Tx primary tumor cannot be evaluated; T0 no evidence of primary tumor; Tis carcinoma in situ: confined to the epithelium or invading the lamina propria; T1 tumor invades the submucosa; T2 tumor invades the lamina propria; T3 tumor penetrates the lamina propria to reach the subplasma layer, or T4a tumor penetrates the visceral layer of the peritoneum; T4b tumor directly invades or adheres to other organs or structures. Nx regional lymph nodes could not be evaluated; N0 no regional lymph node metastasis; N1 1 to 3 regional lymph node metastasis; N1a 1 regional lymph node metastasis; N1b 2 to 3 regional lymph node metastasis; N1c tumor implantation (TD, tumor deposit) in subplasma, mesenteric, peri-rectal tissues without peritoneal coverage, no regional lymph node metastasis; N2 more than 4 regional lymph nodes N2a 4-6 regional lymph node metastases; N2b 7 and more regional lymph node metastases; distant metastases (M); M0 no distant metastases M1 distant metastases M1a distant metastases confined to a single organ or site (e.g. liver, lung, ovary, non-regional lymph nodes) M1b distant metastases distributed to more than one organ/site or peritoneal metastases; Note: 1, clinical TNM staging (cTNM) is the basis for surgical treatment. All information is obtained from physical examination, imaging and pathological biopsy performed to clarify the diagnosis at the first consultation of the primary tumor. Pathological TNM staging (pTNM) is used to assess prognosis and decide whether adjuvant therapy is needed. It integrates clinical staging and pathological findings and is considered the most accurate prognostic assessment standard. Post-neoadjuvant TNM staging (ycTNM or ypTNM) refers to the clinical or pathological staging made after receiving neoadjuvant or preoperative radiotherapy or chemotherapy, and its purpose is to determine the subsequent treatment strategy and judge the treatment effect. Recurrent tumor TNM staging (rTNM) is the information collected when a patient survives tumor-free for a period of time and then relapses, and is the basis for further treatment. Autopsy TNM staging (aTNM) is used for staging cases of tumors that were not found during life and only discovered at autopsy. dukes B stage includes patients with both better prognosis (T3N0M0) and worse prognosis (T4N0M0), and the same for dukes C stage (any TN1M0 and any TN2M0). mac is a modified Astler-Coller stage. 2 , Tis includes tumor cells confined to the basement membrane of the gland (intraepithelial) or to the lamina propria (intramucosa), without crossing the mucosal muscle layer to reach the submucosa. 3 . Direct invasion of T4 includes tumor penetrating the plasma membrane and invading other intestinal segments, which is confirmed by microscopic diagnosis (such as cecum cancer invading sigmoid colon), or tumor located in the retroperitoneum or subperitoneal intestinal canal, which directly invades other organs or structures after penetrating the intrinsic base of the intestinal wall, such as tumor in the posterior wall of the descending colon invading the left kidney or lateral abdominal wall, or tumor in the middle and lower rectum invading the prostate, seminal vesicle gland, cervix or vagina. 4. cT4b if the tumor is visually adherent to other organs or structures, but pT3 if no tumor is present at the site of the adhesion under the microscope. v and L sub-stages are used to indicate the presence of vascular and lymphatic infiltration, while PN is used to indicate nerve infiltration (which can be site-specific).