2.9 Lower Digestive System - Stomach Cancer Cheat Sheet (DRAFT) by Molly

The breaking down of food molecules for use by body cells is called digestion, and the organs that collec­tively perform this function comprise the digestive system.

1. the gastro­int­estinal (GI) tract or alimentary canal and

Gastric cancer was once the second most common cancer in the world. In most developed countries, however, rates of stomach cancer have declined dramat­ically over the past half century.

Decreases in gastric cancer have been attributed in part to widespread use of refrig­era­tion, which has had several beneficial effects: increased consum­ption of fresh fruits and vegeta­bles; decreased intake of salt, which had been used as a food preser­vative; and decreased contam­ination of food, by carcin­ogenic compounds arising from the decay of unrefr­ige­rated meat products.

Nevert­heless, gastric cancer is still the second most common cause of cancer­-re­lated death in the world, and it remains difficult to cure in Western countries, primarily because most patients present with advanced disease. Even patients who present in the most favourable condition and who undergo curative surgical resection often die of recurrent disease.

There are multiple risk factors for the develo­pment of gastric adenoc­arc­inoma, including precursor condit­ions, genetic and enviro­nmental condit­ions, and age. Helico­bacter pylori infection is associated with risk of stomach cancer.

Other known risk factors for stomach cancer include:

Smoking: Smokers are more likely than non-sm­okers to develop stomach cancer. Heavy smokers are most at risk.

Poor diet, lack of physical activity, or obesity: Studies suggest that people who eat a diet high in foods that are smoked, salted, or pickled have an increased risk for stomach cancer. While people who eat a diet high in fresh fruits and vegetables may have a lower risk of this disease.

Approx­imately 95% of all malignant gastric neoplasms are adenoc­arc­inomas, and in general, the term gastric cancer refers to adenoc­arc­inoma of the stomach.

The stomach is a hollow J shaped organ, which begins at the gastro­-es­oph­ageal (GE) junction and ends at the pylorus; it is usually divided into three sections.

The wall of the stomach has five layers. From the lumen out, the layers include the mucosa, the sub-mu­cosa, the muscularis layer, the sub-se­rosal layer, and the serosal layer.

The gastro­-oe­sop­hageal junction has limited or no serosal covering. The right portion of the anterior gastric surface is adjacent to the left lobe of the liver and the anterior abdominal wall.

1. Blood tests – indicates metastatic spread to the liver.

3. CT scan of the abdomen and chest - to ascertain spread to the lungs and liver.

5. Staging laparo­scopy - to determine presence of small cancer nodules and lymph node involv­ement within the abdominal cavity that CT scan can miss. Laparo­scopy is a minor procedure that is done when all other staging procedures are clear. It is done to prevent major surgery being performed in patients whose cancer is not curable.

Staging of gastric cancer is usually performed using the TNM classi­fic­ation system. In the TNM staging system, a score is given for each of the three areas of interest:

Treatment for stomach cancer may involve surgery, chemot­herapy, or radiation therapy.

The majority of patients with operable stage II, IIIA, or IIIB disease have at least a 60% chance of tumour recurrence and death within 5 years of diagnosis. This group therefore might benefit from adjuvant therapy.

Partial (subtotal) Gastre­ctomy for tumours at the lower part of the stomach: The surgeon removes the lower part of the stomach containing the tumour. The surgeon attaches the remaining part of the stomach to the intestine. Nearby lymph nodes and other tissues may also be removed.

The propensity for gastric carcinoma to spread by means of sub-mu­cosal lymphatics suggests that a 5cm margin of normal tissue proximally and distally may be optimal. The 5-year survival rate for a curative surgical resection ranges from 60-90% for patients with stage I, 30-50% for patients with stage II disease, and 10-25% for patients with stage III disease. Due to the high likelihood of local and systemic relapse, some physicians offer adjuvant therapy.

Several chemot­her­apeutic agents have shown activity against gastric adenoc­arc­inoma, including fluoro­uracil, mitomycin, cisplatin, doxoru­bicin and methot­rexate. A standard regime includes the combined use of fluoro­pyr­imidine and cisplatin.

Radiation therapy, usually admini­stered with concom­itant 5-fluo­rou­racil (5-FU)­-based chemot­herapy, is indicated in locally confined gastric cancer that is either not techni­cally resectable or occurs in medically inoperable patients.

The irradi­ation field should include unresected or residual tumour or the tumour bed plus major nodal regions.

With properly shaped fields, doses of 45 to 50.4 Gy in 1.8- to 2.0-Gy fractions can be delivered to stomach and small intestine with a 5% or less risk of severe toxicity.

Target volumes for stomach cancer irradi­ation based on the sites of loco-r­egional failure should include for all patients;

Major nodal chains at risk include lesser and greater curvature, celiac axis, pancreatic duodenal, splenic, suprap­anc­reatic, and porta hepatis.

Parall­el-­opposed antero­pos­ter­ior­-po­ste­roa­nterior (AP/PA) fields are the most practical arrang­ement for the major portion of tumour nodal irradi­ation.

For patients with gastro oesoph­ageal junction or proximal to mid-ga­stric cancers, one half to two thirds of the left kidney can often be spared as a result of accurate field defini­tion, which is aided by pre- and postop­erative imaging studies and clip placement.

However, for distal gastric lesions with narrow or positive duodenal resection margins, the duodenal circum­ference may need to be included as target volume. In such instances 50% or more of the right kidney is within the field, and two thirds to three fourths of the left kidney should be spared. Chronic renal problems are infrequent when these techniques are utilised.

With single daily fractions, the usual dose is 45 to 52 Gy delivered in 1.8- to 2.0-Gy fractions over 5.0 to 5.5 weeks, with a field reduction after 45 Gy. Reduced boost fields to small areas of residual disease can sometimes be cautiously carried to doses of 55 to 60 Gy.

Evidence evaluating the use of radiation therapy in patients with locally recurrent or metastatic carcinoma of the stomach is limited due to small patient numbers. The role of radiation therapy in patients with advanced stomach cancers is likely to be limited to palliation of sympto­ms—such as bleeding or contro­lling pain secondary to local tumour infilt­ration and biliary obstru­ction. Although minimal data is available, radiation therapy seems to be fairly effective (from anecdotal experi­ence) in contro­lling bleeding, as is true in other sites. This can often be accomp­lished at relatively low radiation doses. Pain from local tumour invasion can also be palliated, although the doses required are higher (45 Gy).

Toxicity is often the limiting factor in radiation therapy involving both the lower and upper digestive system.

Late effects consist of fibrotic changes leading to reduced mobility and ischemia.

However, the treatment management approaches for radiation toxicity are mainly supportive care. The increased use of concurrent chemot­herapy and radiation therapy, has required enhanced awareness of potential effects and better methods to decrease toxicity, as this combin­ation of treatments is associated with a higher rate of gastro­-in­tes­tinal toxicity.

Transient mal-ab­sor­ption may occur as a result of diffuse damage to the bowel mucosa in the irradiated field.

Common complaints during gastric irradi­ation include: Anorexia, Nausea, and Fatigue