Depending on glandular architecture, cellular pleomorphism and mucosecretion, adenocarcinoma may present 3 degrees of differentiation: well, moderate and poorly differentiated. Diffuse type adenocarcinoma (mucinous, colloid, linitis plastica or leather-bottle stomach) tumour cells are discohesive and secrete mucus, which is delivered in the interstitium, producing large pools of mucus/colloid (optically "empty" spaces). It is poorly differentiated. In signet-ring cell carcinomas, the mucus remains inside the tumour cell and pushes the nucleus to the periphery, giving rise to signet-ring cells. Around 5% of gastric cancers are lymphomas. These may include extranodal marginal zone B-cell lymphomas (MALT type) and to a lesser extent diffuse large B-cell lymphomas. MALT type make up about half of stomach lymphomas. Carcinoid and stromal tumors may occur. Staging
If cancer cells are found in the tissue sample, the next step is to stage, or find out the extent of the disease. Various tests determine whether the cancer has spread, and if so, what parts of the body are affected. Because stomach cancer can spread to the liver, pancreas, and other organs near the stomach, as well as to the lungs, the doctor may order a CT scan, a PET scan, an endoscopic ultrasound exam, or other tests to check these areas. Blood tests for tumor markers, such as carcinoembryonic antigen and carbohydrate antigen may be ordered, as their levels correlate to extent of metastasis, especially to the liver, and the cure rate.Staging may not be complete until after surgery.
The exact mechanism by which obesity causes GERD is not completely known. Studies hypothesize that increased dietary fat leading to increased pressure on the stomach and the lower esophageal sphincter, due to excess adipose tissue, could play a role, yet no statistically significant data have been collected. However, the risk of gastric cardia adenocarcinoma, with GERD present, has been found to increase more than 2 times for an obese person. There is a correlation between iodine deficiency and gastric cancer. Genetics
About 10% of cases run in families, and between 1 and 3% of cases are due to genetic syndromes inherited from a persons parents such as hereditary diffuse gastric cancer.A genetic risk factor for gastric cancer is a genetic defect of the CDH1 gene known as hereditary diffuse gastric cancer (HDGC). The CDH1 gene, which codes for E-cadherin, lies on the 16th chromosome. When the gene experiences a particular mutation, gastric cancer develops through a mechanism that is not fully understood. This mutation is considered autosomal dominant, meaning that half of a carriers children will likely experience the same mutation. Diagnosis of hereditary diffuse gastric cancer usually takes place when at least two cases involving a family member, such as a parent or grandparent, are diagnosed, with at least one diagnosed before the age of 50. The diagnosis can also be made if at least three cases occur in the family, in which case age is not considered.The International Cancer Genome Consortium is leading efforts to identify genomic changes involved in stomach cancer.