___________________________________________________________________________ Colorectal Cancer
AMERICAN JOINT COMMISSION ON CANCER TNM CLASSIFICATION FOR COLON AND RECTAL CANCER
Code
Description
Primary Tumor (T) TX
Primary tumor cannot be evaluated No evidence of primary tumor
T0 Tis T1 T2 T3
Carcinoma in situ
Tumor extends through the mucosa and into the submucosa Tumor extends through the submucosa and into muscularis propria Tumor extends through the muscularis propria and into the subserosa but not to any neighboring organs or tissues Tumor penetrates to the surface of the visceral peritoneum Tumor directly invades or is adherent to adjacent organs or structures
T4a T4b
Regional Lymph Node Involvement (N) NX
Regional lymph nodes cannot be evaluated
N0 N1
No regional nodal involvement
Metastasis in 1–3 regional lymph nodes Metastasis in 1 regional lymph node Metastasis in 2–3 regional lymph nodes
N1a N1b N1c
Tumor deposit(s) in the subserosa, mesentery, or nonperitonealized pericolorectal tissues without regional nodal metastasis
N2
Metastasis in 4 or more regional lymph nodes Metastasis in 4–6 regional lymph nodes Metastasis in 7 or more regional lymph nodes
N2a N2b
Distant Metastasis (M) M0
No distant metastasis Distant metastasis
M1
M1a M1b
Metastasis confined to one organ or site
Metastasis in more than one organ/site or the peritoneum
Source: [204]
Table 6
Imaging Modality After colorectal cancer is diagnosed, additional imaging is required for disease staging. Liver and chest imaging, prefer- ably using CT, is necessary to detect metastases. Rectal cancers should be staged using endorectal ultrasonography or MRI. Positron emission tomography (PET) imaging is increasingly used in colorectal cancer to detect extrahepatic metastases in patients considered for hepatic resection of presumed liver- only metastatic disease. PET is also used to localize disease in patients thought to have a recurrence, as reflected by emergent symptoms or rising CEA [174; 200; 201]. PET is generally not recommended for routine colon cancer staging [190]. Practice guideline recommendations for imaging to stage colorectal cancer have been published by the American Society of Colon and Rectal Surgeons (ASCRS) and by Cancer Care
Ontario [190; 202]. They recommend contrast-enhanced CT of the chest, abdomen, and pelvis should be performed in all patients with colon cancer (unless contraindicated) to estimate disease stage and identify metastases. If local exci- sion is considered for low rectal cancer (0–5 cm from the anal verge), transrectal ultrasonography is preferred over MRI to improve discrimination between T1 and T2 lesions. For upper rectal cancers (10–15 cm above the anal verge), whereby the mesorectal fascia is not threatened, MRI is not considered superior to pelvic CT. MRI can stage the local rectum but is not adequate to assess regional disease at the level of the inferior mesenteric artery or distant disease. CT of the abdomen and pelvis should be used to assess for distant metastases and regional disease, including lymph node involvement along the inferior mesen-
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