Gastric adenocarcinoma HER2 negative, usually is the result of immunohistochemistry examination of gastric cancer, its negative means that the protein is not expressed, it is one of the bases for guiding the choice of treatment for gastric cancer, usually has no direct relationship with whether the disease is serious or not, whether it is serious or not depends on the staging and differentiation degree. Gastric adenocarcinoma HER2 negative refers to the negative result of immunohistochemistry test, which means that the protein is not expressed. Gastric cancer patients with this test result are not suitable for trastuzumab and other targeted drug treatments, but it does not reflect the severity of the disease. Whether gastric adenocarcinoma is serious or not mainly depends on the staging of the tumor, and the degree of differentiation of the tumor. Relatively speaking, the later the tumor stage and the worse the differentiation degree, the more serious the condition is. If gastric adenocarcinoma is HER2 negative, reasonable treatments can be chosen according to the staging, such as surgical treatment, chemotherapy, radiotherapy and so on. If gastric adenocarcinoma is detected, please go to regular hospitals in time and choose appropriate treatments under doctor’s guidance to avoid delaying the condition.