Colorectal cancer, hepatocellular carcinoma and gastric malignancy are three of the most common gastrointestinal cancers in Asia.

Colorectal cancer most likely results from a complex interplay of environmental and genetic factors. Genetic predisposition is emerging as an increasingly important risk factor for colorectal cancer, beyond those associated with a known neoplastic syndrome (i.e. familial adenomatous polyposis).

Typical presenting features depend on the site and stage of the tumor. Anemia of unexplained origin, rectal bleeding, and altered bowel habit are the common presenting features.

The regional lymph nodes and the liver are the main sites for metastasis

The definitive treatment is resection. Adjuvant chemotherapy or radiotherapy may be indicated, depending on the site and stage of the tumor.

Prognosis depends on the stage at the time of diagnosis. Improved survival rates are probably secondary to screening and ability to identify premalignant and early neoplastic disease.

Staging of colorectal cancer is based on the tumor-node-metastases (TNM) staging system

The TNM classification has five stages (0–IV):

• Stage 0 – carcinoma in situ (Tis, N0, M0)
• Stage I (Dukes' stage A) – tumor invades the submucosa or muscularis propria (T1–2, N0, M0)
• Stage II (Dukes' stage B) – tumor invades through the muscularis propria into the subserosa, pericolonic, or perirectal tissue, or invades adjacent structures and/or perforates the visceral peritoneum (T3–4, N0, M0)
• Stage III (Dukes' stage C) – primary tumors at any level of invasion with involvement of local lymph nodes (any T, N1–2, M0)
• Stage IV (Dukes' stage D) – primary tumors at any level of invasion, local lymph node involvement and distant metastases (any T, any N, M1)

Hepatocellular carcinoma (HCC) is one of the most common types of cancer in Asia where chronic hepatitis or liver diseases are prevalent. Men are more likely to develop this disease, as are patients with cirrhosis or a chronic liver disease such as hepatitis B or hepatitis C.

Usually asymptomatic until late stages of the disease; symptoms usually include abdominal pain and an abdominal mass, and may also include fever, anorexia, stomach fullness, edema, and jaundice.

Prognosis is generally very poor, with less than 5% of symptomatic patients surviving for more than 2 years.

Treatments include total surgical resection if possible, systemic chemotherapy such as multikinase inhibitor, hepatic arterial chemotherapy, hepatic arterial chemoembolization, radiation therapy, percutaneous ethanol injection, radiofrequency ablation, and liver transplantation.

Screening at-risk patients (cirrhotic disease, chronic hepatitis B or C infection, or other liver injury) with alpha-fetoprotein tests and ultrasound may detect disease in early stages. Preventive measures include hepatitis B vaccination, elimination of aflatoxin exposure, and decreased alcohol intake.

Gastric carcinoma are divided into intestinal and diffuse forms, each with its own prognostic factors.

• About 95% of gastric cancers are adenocarcinomas; the rest are leiomyosarcomas, lymphomas, carcinoids, squamous cancers, or other rarer types
• Intestinal-type gastric cancers are usually well differentiated, have more distal location, occur in younger patients, are more frequently endemic, and are associated with inflammatory changes and with H. pylori infection
• Diffuse-type gastric cancer is associated with hereditary factors and a proximal location and does not appear to occur in the setting of intestinal metaplasia or dysplasia. Diffuse-type generally occurs in patients <50 years of age and is more common in women. Diffuse-type gastric cancer is usually less differentiated and thickens the stomach wall (linitis plastica, 'leather bottle' stomach) rather than forming a discrete tumor mass. It carries a poorer prognosis than intestinal-type gastric cancer
• Often clinically silent with nonspecific complaints, and often diagnosed at late stage
• Double-contrast gastric radiograph followed by endoscopic biopsy is the typical diagnostic protocol
• Endoscopy with multiple biopsies is the primary diagnostic modality
• Poor prognosis overall, with 5-year survival rate of 23% in a series of patients 1995-2001
• Prognosis is dependent on the degree of invasion, extension, and spread. Other factors include location of the tumor and tumor histology
• Treatment is primarily surgical, and either total or subtotal gastrectomy with regional lymphadenectomy offers the only hope of cure
• Postoperative chemoradiation using 5-fluorouracil and leucovorin is now the standard of care for resected patients able to tolerate such treatment

GIST tumors (gastrointestinal stromal tumors) are the most common mesenchymal tumor in the digestive tract

• Most gastrointestinal mesenchymal tumours, previously classified as leiomyomas, schwannomas or leiomyosarcomas, are today classified as GISTs on the basis of molecular and immunohistological features, which may be of spindle cell, epitheliod or mixed cell type
• The great majority of GISTs occur in the stomach, in particular the fundus (60%–70%) and small intestine (25%–35%)
• Most small GIST tumors are symptomatic. Large lesions can ulcerate and bleed
• Mutation with increased activation of the of the c-kit (tyrosine kinase receptor) is strongly associated with pathogenesis; familial c-kit mutations are seen. As such they are usually imatinib sensitive
• Histologically, the tumor may be of spindle cell, epitheliod or mixed cell type; immunochemistry with CD117 and CD34 is useful in the diagnosis of GIST