Stomach cancer (gastric cancer)

Stomach cancer, also called gastric cancer, starts in the cells that line the inside of the stomach. Nearly all of these cancers are adenocarcinomas, meaning they begin in the cells that make the mucus coating that lining. Under the microscope, stomach cancer shows up in two main forms, intestinal and diffuse, and it helps to look at each separately.

In the intestinal type, the cancer cells arrange themselves into glands, which are tiny hollow structures, like little tubes built out of cells. The most common trigger for this type is Helicobacter pylori, a kind of bacterium. And the evidence suggests this type doesn't appear all at once but develops over time. First comes dysplasia, in which cells already look abnormal but aren't cancer yet. Later comes carcinoma, which is cancer.

The diffuse type works differently. Its cells are missing adhesion molecules, which act like the glue that keeps cells stuck together, and they usually don't build glands. This type can spread into the submucosa, the layer just beneath the stomach's inner lining, without forming a mass, meaning a lump. Picture a drop of ink on a paper napkin: instead of sitting on top as a drop, it seeps in between the fibers and spreads out. When the stomach has been infiltrated this way, its appearance is called linitis plastica.