Colon Cancer

Colon cancer is the most common type of gastrointestinal cancer. It is a multifactorial disease process, with etiology encompassing genetic factors, environmental exposures (including diet), and inflammatory conditions of the digestive tract.

Surgery currently is the definitive treatment modality. The image below depicts standard colectomies for adenocarcinoma of the colon.

Standard colectomies for adenocarcinoma of the colon.

See Cutaneous Clues to Diagnosing Metastatic Cancer, a Critical Images slideshow, to help identify various skin lesions that are cause for concern.

Signs and symptoms

Colon cancer is now often detected during screening procedures. Other common clinical presentations include the following:

• Iron-deficiency anemia
• Rectal bleeding
• Abdominal pain
• Change in bowel habits
• Intestinal obstruction or perforation

Physical findings may include the following:

• Early disease: Nonspecific findings (fatigue, weight loss) or none at all
• More advanced disease: Abdominal tenderness, macroscopic rectal bleeding, palpable abdominal mass, hepatomegaly, ascites

See Clinical Presentation for more detail.

Diagnosis

Laboratory studies that may be helpful include the following:

• Complete blood count
• Chemistries and liver function tests
• Serum carcinoembryonic antigen

Imaging studies that may facilitate staging include the following:

• Chest radiography
• Chest computed tomography
• Abdominal barium study
• Abdominal/pelvic CT
• Contrast ultrasonography of the abdomen and liver
• Abdominal/pelvic MRI
• Positron emission tomography, including fusion PET-CT scan

Other procedures that may be warranted include the following:

• Colonoscopy
• Sigmoidoscopy
• Biopsy of suspicious lesions
• Double-contrast barium enema

Current TNM classification is as follows:

• Tx – No description of tumor extent possible, because of incomplete information
• Tis – In situ carcinoma; tumor involves only muscularis mucosa
• T1 – Cancer has grown through muscularis mucosa and extends into submucosa
• T2 – Cancer has grown through submucosa and extends into muscularis propria
• T3 – Cancer has grown through muscularis propria and into outermost layers of colon but not through them; it has not reached any nearby organs or tissues
• T4a – Cancer has grown through serosa (visceral peritoneum)
• T4b – Cancer has grown through wall of colon and is attached to or invades nearby tissues or organs
• Nx – No description of lymph node involvement possible, because of incomplete information
• N0 – No cancer in nearby lymph nodes
• N1a – Cancer cells found in 1 nearby lymph node
• N1b – Cancer cells found in 2-3 nearby lymph nodes
• N1c – Small deposits of cancer cells found in areas of fat near lymph nodes, but not in lymph nodes themselves
• N2a – Cancer cells found in 4-6 nearby lymph nodes
• N2b – Cancer cells found in 7 or more nearby lymph nodes
• M0 – No distant spread seen
• M1a – Cancer has spread to 1 distant organ or set of distant lymph nodes
• M1b – Cancer has spread to more than 1 distant organ or set of distant lymph nodes, or has spread to distant parts of the peritoneum

Staging is as follows:

Table 1. TNM Staging System for Colon Cancer (Open Table in a new window)

Stage	Primary Tumor (T)	Regional Lymph Node (N)	Remote Metastasis (M)
Stage 0	Carcinoma in situ (Tis)	N0	M0
Stage I	Tumor may invade submucosa (T1) or muscularis propria (T2)	N0	M0
Stage II	Tumor invades muscularis (T3) or adjacent organs or structures (T4)	N0	M0
Stage IIA	T3	N0	M0
Stage IIB	T4a	N0	M0
Stage IIC	T4b	N0	M0
Stage IIIA	T1-4	N1-2	M0
Stage IIIB	T1-4	N1-2	M0
Stage IIIC	T3-4	N1-2	M0
Stage IVA	T1-4	N1-3	M1a
Stage IVB	T1-4	N1-3	M1b

See Workup for more detail.

Management

Surgery is the only curative modality for localized colon cancer (stage I-III). Surgical resection potentially provides the only curative option for patients with limited metastatic disease in liver and/or lung (stage IV disease). Surgical options include the following:

• Right hemicolectomy: For lesions in the cecum and right colon
• Extended right hemicolectomy: For lesions in the proximal or middle transverse colon
• Left hemicolectomy: For lesions in the splenic flexure and left colon
• Sigmoid colectomy: For sigmoid colon lesions
• Total abdominal colectomy with ileorectal anastomosis: For selected patients with hereditary nonpolyposis colon cancer, attenuated familial adenomatous polyposis, metachronous cancers in separate colon segments, or acute malignant colon obstructions with unknown status of the proximal bowel

Other therapeutic options for patients who are not surgical candidates include the following:

• Cryotherapy
• Radiofrequency ablation
• Hepatic arterial infusion of chemotherapeutic agents

Regimens used for systemic chemotherapy may include the following:

• 5-Fluorouracil (5-FU)
• Capecitabine
• Tegafur
• Oxaliplatin
• Irinotecan
• Combinations of multiple agents (eg, capecitabine or 5-FU with oxaliplatin, 5-FU with leucovorin and oxaliplatin)

Regimens used for adjuvant (postoperative) chemotherapy commonly include 5-FU with leucovorin or capecitabine, either alone or in combination with oxaliplatin.^{[1, 2, 3]}

Biologic agents employed to treat colon cancer include the following:

• Bevacizumab (Avastin)
• Cetuximab (Erbitux)
• Panitumumab (Vectibix)
• Ramucirumab (Cyramza)
• Regorafenib (Stivarga)
• Ziv-aflibercept (Zaltrap)