CONDITION
Gastric Adenocarcinoma
Gastric adenocarcinoma is a type of cancer that arises from the glandular cells lining the stomach. These cells normally produce mucus and digestive fluids, but when they become cancerous, they can form masses or thicken the stomach wall in ways that interfere with normal digestion and movement of food. It occurs most commonly in older dogs, with certain breeds appearing more susceptible, and is less frequently diagnosed in cats. Owners often arrive at this page because their dog or cat has been vomiting intermittently, losing weight despite a reasonable appetite, or showing a gradual decline in energy and interest in food. These signs can develop slowly over weeks or months, and may initially be mistaken for less serious digestive upset. In some cases, the condition is discovered during investigation of anaemia or abdominal discomfort. This page explores the signals that may prompt investigation, what is happening at a tissue and cellular level, how the condition is identified through imaging and biopsy, and the range of approaches that exist—including surgery, chemotherapy, and supportive care—each with its own considerations and limitations.
Why this matters now
Gastric adenocarcinoma tends to appear in dogs over seven years of age, with the highest incidence in animals between eight and ten years old. Certain breeds including Belgian Shepherds, Rough Collies, Staffordshire Bull Terriers, and Chow Chows appear to be diagnosed more frequently, though the condition can occur in any breed. Male dogs may be affected slightly more often than females. In cats, the condition is less common and the age and breed patterns are less clearly defined.
The condition often develops slowly over several months before signs become noticeable enough to prompt investigation. Early changes in the stomach lining may cause subtle digestive disturbance that owners attribute to dietary indiscretion or minor gastritis. As the tumour grows or spreads through the stomach wall, signs typically become more persistent and the animal's condition may decline more noticeably. The rate of progression can vary considerably between individuals.
Signals & patterns
Early signals
Intermittent vomiting
Vomiting may occur sporadically, sometimes hours after eating, and may contain undigested food or frothy liquid. The pattern can be inconsistent enough that it does not initially seem linked to a single underlying cause.
Gradual weight loss
Weight may decline slowly over weeks or months, even when the animal appears to be eating reasonable amounts. The loss can be subtle at first, particularly in dogs with thick coats or cats who are not weighed regularly.
Reduced appetite or selective eating
Interest in food may wane gradually, with the animal becoming pickier or eating smaller portions than usual. Some animals will eat normally for days, then refuse food for a day or two, creating an unpredictable pattern.
Decreased energy or enthusiasm
Activity levels may drop in ways that are easy to attribute to normal ageing, such as less interest in play, shorter walks, or more time spent resting. The change is often gradual enough that it becomes the new normal before it is recognised as a shift.
Later signals
Persistent or worsening vomiting
Vomiting may become more frequent and predictable, often occurring shortly after meals. In some cases, the stomach's ability to empty becomes significantly impaired, leading to vomiting of larger volumes.
Visible abdominal discomfort
The animal may show reluctance to be touched around the abdomen, adopt a hunched posture, or seem restless and unable to settle comfortably. These signs can suggest pain or nausea.
Dark or tarry faeces
Stools may become darker or have a tar-like consistency, which can indicate digested blood from bleeding within the stomach. This sign often appears alongside other digestive disturbances.
Pronounced weakness or collapse
Advanced disease or significant internal bleeding can lead to pale gums, weakness, and in some cases episodes of collapse. These signs reflect anaemia or systemic compromise.
Click to read about the biological mechanisms
How this is usually investigated
Options & trade-offs
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