When a dog starts skipping meals, vomiting more than usual, or acting uncomfortable after eating, many owners chalk it up to an upset stomach. But sometimes these subtle changes signal a more serious issue. Stomach cancer—most commonly gastric adenocarcinoma or lymphoma—can be aggressive, and catching it early gives you more treatment options and a better chance at a positive outcome.
Stomach cancer develops when abnormal cells in the stomach lining multiply and form tumors that interfere with digestion. These growths can cause bleeding, blockages, and may spread to nearby organs such as the liver or lymph nodes. While not the most common cancer in dogs, it is serious and most frequently occurs in middle-aged to older animals.
Because the early symptoms often resemble minor digestive problems, owners must pay attention to patterns and persistence. Here are ten signs that warrant a veterinary exam:
If your dog refuses food for five days or more—even their favorite treats—this is more than temporary picky behavior. Cancer-related appetite loss often doesn’t respond to food swaps, changes in schedule, or coaxing.
A drop of roughly 10% or more of body weight within a short period is alarming. Watch for ribs or spine becoming more pronounced and decreased muscle mass around the hips.
Vomiting several times per week, especially hours after eating, may point to a stomach issue. Vomit that contains bright red blood or resembles coffee grounds signals digested blood and requires immediate attention.
Dogs in gastric pain may assume a "prayer position" (front legs down, hind end raised), avoid jumping, move stiffly, or flinch when the belly is touched. These behaviors often start small and worsen over time.
Dark, sticky stools with a metallic odor usually indicate bleeding higher in the digestive tract. Photographing abnormal feces can help your veterinarian determine the source.
If food returns shortly after eating, or your dog repeatedly adjusts their head while trying to swallow, an upper-stomach mass could be obstructing the passage from the esophagus.
Marked lethargy—sleeping excessively, avoiding walks, or taking far shorter routes than usual—can be a sign that something is wrong. Comparing current activity levels to your dog’s normal baseline helps identify a decline.