From OMIM
Diffuse gastric cancer and lobular breast cancer syndrome (DGLBC) is an autosomal dominant cancer predisposition syndrome. Heterozygous CDH1 mutation carriers have a 70 to 80% lifetime risk of developing diffuse gastric cancer. In addition to gastric cancer, up to 60% of female mutation carriers develop lobular carcinoma of the breast, and some carriers may develop colorectal cancer. Identification of mutation carriers is important, because the characteristic microscopic foci of signet ring cell adenocarcinoma in HDGC usually involves the submucosa and is often not readily detectable by routine upper endoscopy screening (summary by Fitzgerald et al., 2010). DGLBC is considered to be a distinct disease entity from the more common sporadic occurrence of gastric cancer (613659), which can be associated with environmental factors such as Helicobacter pylori infection, high-fat diet, or smoking and is often associated with somatic mutations in disease tissue.  http://www.omim.org/entry/137215

From MedlinePlus Genetics
Hereditary diffuse gastric cancer (HDGC) is an inherited disorder that greatly increases the chance of developing a form of stomach(gastric) cancer. In this form, known as diffuse gastric cancer, there is no solid tumor. Instead cancerous (malignant) cells multiply underneath the stomach lining, making the lining thick and rigid. The invasive nature of this type of cancer makes it highly likely that these cancer cells will spread (metastasize) to other tissues, such as the liver or nearby bones.

Symptoms of diffuse gastric cancer occur late in the disease and can include stomach pain, nausea, vomiting, difficulty swallowing (dysphagia), decreased appetite, and weight loss. If the cancer metastasizes to other tissues, it may lead to an enlarged liver, yellowing of the eyes and skin (jaundice), an abnormal buildup of fluid in the abdominal cavity (ascites), firm lumps under the skin, or broken bones.

In HDGC, gastric cancer usually occurs in a person's late thirties or early forties, although it can develop anytime during adulthood. If diffuse gastric cancer is detected early, the survival rate is high; however, because this type of cancer is hidden underneath the stomach lining, it is usually not diagnosed until the cancer has become widely invasive. At that stage of the disease, the survival rate is approximately 20 percent.

Some people with HDGC have an increased risk of developing other types of cancer, such as a form of breast cancer in women that begins in the milk-producing glands (lobular breast cancer); prostate cancer; and cancers of the colon (large intestine) and rectum, which are collectively referred to as colorectal cancer. Most people with HDGC have family members who have had one of the types of cancer associated with HDGC. In some families, all the affected members have diffuse gastric cancer. In other families, some affected members have diffuse gastric cancer and others have another associated form of cancer, such as lobular breast cancer. Frequently, HDGC-related cancers develop in individuals before the age of 50.  https://medlineplus.gov/genetics/condition/hereditary-diffuse-gastric-cancer