In general, a blood test and normal radiography are not sufficient to make a diagnosis.
Generally, the blood test does not show specific evidence for gastric adenocarcinoma. It may help to detect certain side effects or to distinguish them from other tumor types.
By contrast radiography of the stomach, a growth that should not be present in the stomach can be discovered. It is also possible to find a stomach ulcer, which often occurs with gastric adenocarcinomas. Alternatively, the stomach may empty more slowly than usual (the contrast material moves more slowly than usual).
Via an ultrasound the veterinarian can collect a sample from more difficult to reach places with a needle. The location of the tumor may be a possible indicator of the tumor type. Gastric adenocarcinomas tend to occur more at the level of the gastric outlet, while leiomyosarcomas are more common at the level of the stomach entrance.
By sliding a flexible tube into the stomach of the dog, the veterinarian can visualize growths and take extensive samples in a targeted manner (the surface of a stomach tumor is often unusable for analysis because, e.g. the tissue may be ulcerated).
This is the surest way to obtain a good sample of the tumor.
If there is a suspicion of a GIST (gastrointestinal stromal tumor), a CD117 staining is done to confirm or not. This is a rare tumor that arises from the support tissue of the gastrointestinal tract.
Thanks to these studies, it can be determined whether the tumor is malignant or very aggressive. This information will help determine if additional treatments are needed.