Gastrointestinal (GI) cancer in canines is a term used to describe various abnormal growths stemming from tissues in the digestive system. Dog GI cancers are rare but locally invasive and metastasizing. 

Common malignant gastrointestinal tumors are adenocarcinoma, lymphoma, leiomyosarcoma, gastrointestinal stromal tumors (GISTs), and mast cell tumors. 

Gastrointestinal cancer in dogs is caused by genetic and environmental factors, with age, breed, sex, and dietary habits being contributing factors. 

Vomiting and diarrhea with or without blood, drooling, anorexia, appetite loss, and abdominal pain and distension are standard symptoms of GI cancer in dogs.  

Gastrointestinal cancer in dogs is diagnosed with biopsy combined with bloodwork and imaging techniques like X-rays and ultrasounds. 

The treatment for dog stomach cancer and intestinal cancer entails surgery, chemotherapy, and radiation. The median survival rate for dogs with GI cancer is several months. 

What is gastrointestinal cancer in dogs?

Gastrointestinal cancer in dogs is a collection of tumors arising from stomach and intestinal tissues. The majority of tumors of the gastrointestinal (GI) tract are malignant. 

GI cancer in dogs is rare but devastating. The signs of digestive tract tumors are non-specific, and by the time a diagnosis is made, they are advanced. 

Cancers of the dog’s gastrointestinal system are locally invasive, form metastases, and regrow after treatment. The general GI cancer prognosis is guarded to poor. 

What are other terms for gastrointestinal cancer in dogs?

Other terms for gastrointestinal cancer in dogs are stomach cancer and intestinal cancer. GI cancers in dogs are classified as benign or malignant. 

Gastrointestinal cancers are named based on type. A malignant GI tumor arising from glandular tissue is called an adenocarcinoma, while a benign glandular tumor is an adenoma. 

Certain cancers, such as gastrointestinal stromal tumors (GISTs), feature terms explaining their location and type. 

What are the common types of gastrointestinal cancers found in dogs?

The common types of gastrointestinal cancer found in dogs are listed below. 

• Adenocarcinoma: Adenocarcinoma is a malignant, invasive, and metastatic tumor that rises from epithelial tissues and affects various parts of the digestive tract. 
• Lymphoma: Alimentary lymphoma is a lymphoid tissue tumor of the GI tract that causes digestive symptoms. 
• Leiomyosarcoma: Leiomyosarcoma is a rare but painful malignant tumor in dogs that originates from the soft muscles of the stomach and intestines. 
• Gastrointestinal Stromal Tumors (GISTs): GI stromal tumors are a submucosal type of cancer that forms from intestinal pacemaker cells called "interstitial cells of Cajal.”
• Mast Cell Tumors: Mast cell tumors comprise mutated mast cells, which invade the dog’s gastrointestinal tract in sporadic cases. 

1. Adenocarcinoma

Adenocarcinoma is a malignant tumor arising from glandular tissue. The tumor is highly invasive and forms metastasis. Adenocarcinoma develops on all GI tract parts but is the most common and dangerous on the stomach. 

Stomach adenocarcinoma has the worst prognosis compared to other GI cancers. The goal of the treatment is to reduce the symptoms and keep the dog comfortable for as long as possible. 

2. Lymphoma

Lymphoma is a type of tumor originating from white blood cells or lymphocytes. The condition is called alimentary lymphoma when affecting the digestive tract. 

Alimentary lymphoma is rare and causes gastrointestinal problems like vomiting and diarrhea. Localized lymphoma has a better prognosis than general lymphoma and other GI cancers. The median survival rate for dogs with alimentary lymphoma is one year. 

3. Leiomyosarcoma

Leiomyosarcoma is a malignant tumor stemming from soft muscles in the stomach or intestines. Canine leiomyosarcoma is the second most common GI cancer in dogs.

Leiomyosarcoma is excruciatingly painful and prone to metastasizing. Local leiomyosarcoma has a good prognosis when caught early. Advanced leiomyosarcoma has a similar malignancy level as adenocarcinoma. 

4. Gastrointestinal Stromal Tumors (GISTs)

Gastrointestinal stromal tumors (GISTs) are specific mesenchymal tumors. GISTs originate from intestinal pacemaker cells known as interstitial cells of Cajal. 

GI stromal tumors develop anywhere in the digestive tract but are most prevalent in the cecum or first part of the large intestine. The behavior of GISTs ranges from asymptomatic to highly metastasizing and attacking the liver. GISTs have a regrowing tendency after removal. 

5. Mast Cell Tumors

Mast cell tumors or mastocytomas are abnormal growths arising from mast cells. Mast cells are part of the dog’s immune system and safeguard against viruses and parasites. 

Mastocytomas are primary skin tumors but develop in the gastrointestinal tract in rare cases. The upper parts of the digestive system are frequently affected. GI mast cell tumors thicken the intestinal wall, cause lumen narrowing, and have a poor prognosis. 

How does gastrointestinal cancer develop in dogs?

Gastrointestinal cancer develops in dogs gradually over several weeks or months. The average age of onset is between six and nine years. 

The cancer starts manifesting with vomiting. Telltale digestive upset signs unravel as the issue progresses. Gastrointestinal cancer usually advances by the time it is diagnosed.

How common is gastrointestinal cancer in dogs?

Gastrointestinal cancer in dogs is rare. "Overall, digestive tract tumors are uncommon in dogs and cats, comprising approximately 2% of cancers in pets," reports an article “Intestinal Tumors” published by VCA Hospitals. 

The top three gastrointestinal cancers are adenocarcinoma, lymphoma, and leiomyosarcoma. Adenocarcinomas are most common in the stomach and large intestine, while leiomyosarcoma is found in the small intestine. Lymphoma develops anywhere in the GI tract. 

Gastrointestinal cancer is rare in puppies and cats. Lymphoma of the small intestine is the most frequent feline GI cancer. 

Which breeds are more prone to developing gastrointestinal cancer?

The breeds more prone to developing gastrointestinal cancer are listed below. 

• German Shepherds: German Shepherds are overrepresented in digestive tract cancer studies and are prone to various types of gastrointestinal tumors. 
• Rough Collies: Rough Collie members are at a higher-than-average risk of developing different forms of gastrointestinal cancer. 

What does gastrointestinal cancer in dogs look like?

Gastrointestinal cancer in dogs looks like persistent vomiting, diarrhea, weight loss, decreased appetite, and abdominal pain or swelling. Signs include visible blood in vomit or stool and a noticeable abdominal mass.

How do the type and stage of cancer affect the prognosis?

The type and stage of cancer affect the prognosis by determining the course of the condition. The GI tract cancer type determines whether it is benign or malignant. 

The staging evaluates the advancement of malignant tumors. Dog cancer is classified into four stages, from I to IV. Staging is determined based on the tumor location, size, lymph node involvement, and spreading to distant body parts or metastasis. 

What are the causes of gastrointestinal cancer in dogs?

The causes of gastrointestinal cancer in dogs are listed below. 

• Genetics: Specific gastrointestinal cancer types are widespread among certain breeds, indicating a genetic component. 
• Environmental Factors: Long-term exposure to chemicals, secondhand smoke, and airborne pollutants is associated with cancer development. 
• Dietary Choices: Low-quality dog food formulas made with artificial preservatives and additives are believed to contribute to GI cancer. 
• Chronic Gastroenteritis: Recurrent or chronic inflammation of the gastrointestinal tract predisposes dogs to cancer. 

Are there genetic factors that contribute to GI cancer in dogs?

Yes, there are genetic factors that contribute to GI cancer in dogs. The high incidence of cancer of the stomach and intestines in specific dog breeds confirms the genetic link. 

GI cancer is present in multiple dogs over several generations of the same breeding stock. The inheritance mode is unknown, and researchers are investigating the genes responsible for it. 

What are the symptoms of gastrointestinal cancer in dogs?

The symptoms of gastrointestinal cancer in dogs are listed below.

• Vomiting: Vomiting is one of the earliest signs of gastrointestinal cancer. The vomit, in some dogs, contains blood, which is called hematemesis. 
• Diarrhea or Constipation: Gastrointestinal cancer causes diarrhea or constipation, with or without blood. Blood in the stool is dark and resembles coffee grounds when it originates from the upper GI tract (melena) or bright red when it originates from the lower GI tract (hematochezia). 
• Drooling: Excessive drooling or hypersalivation is commonly reported and indicates a feeling of nausea. 
• Anorexia: Significantly reduced or completely lost appetite (anorexia) is one of the main stomach cancer symptoms in dogs. 
• Weight Loss: The decline in appetite combined with abnormal digestion results in weight loss in dogs with gastrointestinal cancer. 
• Abdominal Pain: The abdomen of dogs with GI cancer is painful and visibly distended in some cases. 

When do symptoms of gastrointestinal cancer typically occur in dogs?

The symptoms of gastrointestinal cancer typically occur in dogs when the tumor starts growing. The initial signs are non-specific. 

Early-stage GI cancer symptoms mimic gastrointestinal distress, delaying diagnosis. Schedule a veterinary consultation for dogs with intermittent signs of stomach upset. Prompt diagnosis affects the dog’s prognosis. 

What are the risk factors for gastrointestinal cancer in dogs?

The risk factors for gastrointestinal cancer in dogs are listed below. 

• Age: Malignant and benign gastrointestinal tumors are prevalent in middle-aged and older dogs, making age a significant contributing factor. 
• Breed: Certain dog breeds, such as German Shepherds, Rough Collies, Chow Chows, and Belgian Terevurens, are predisposed to GI cancer. 
• Sex: Stomach and intestinal cancer in dogs occurs more frequently in males than females. 

What are the complications of gastrointestinal cancer in dogs?

The complications of gastrointestinal cancer in dogs are listed below. 

• Metastases: The main complication of GI cancer in dogs is spreading to distant tissues and organs or metastasizing. 
• Ascites: Stomach cancer causes an accumulation of fluids in the abdomen, medically termed ascites. The fluid buildup pressures surrounding tissues. 
• Mechanical Obstruction: Tumors in the intestines, especially large growths, physically block food passage through the digestive tract. 
• Ulcers: Certain types of GI cancer are ulcerative and perforate the walls of the digestive tract, leaking content into the abdomen and causing a life-threatening infection. 

Where can you seek a diagnosis for gastrointestinal cancer in dogs?

You can seek a diagnosis for gastrointestinal cancer in dogs at a veterinary clinic. The veterinarian examines the dog and recommends additional tests based on initial findings. 

The general veterinary practitioner refers the dog to an oncology vet in more severe cases. The oncologist determines the dog’s cancer type and stage. A treatment strategy is developed based on the findings.  

How is gastrointestinal cancer diagnosed in dogs?

Gastrointestinal cancer in dogs is diagnosed with a biopsy. Biopsy samples are collected with laparoscopy or laparotomy. 

Laparoscopy is less invasive and uses an endoscope, while laparotomy is a surgical procedure that involves opening the dog’s abdomen. Fine needle aspiration, or FNA, is feasible in some dogs with gastric cancer. 

Other diagnostic procedures helpful in staging the cancer are plain and contrast X-rays of the abdomen, abdominal ultrasound, chest X-rays, blood counts, and biochemistry profiles. 

Are there early detection methods for GI cancer in dogs?

Yes, there are early detection methods for GI cancer in dogs. A next-generation screening test is being developed for preclinical cancer diagnosis, reports a study, “Cancer Detection in Clinical Practice and Using Blood‐Based Liquid Biopsy: A Retrospective Audit of over 350 Dogs,” published in the Journal of Veterinary Internal Medicine in 2023. 

The procedure is called a liquid biopsy because it uses a blood sample. The method’s potential uses are groundbreaking. Currently, 88% of canine cancer cases are diagnosed after the owner reports worrisome signs, at which time the cancer is advanced.  

What is the prognosis for dogs diagnosed with GI cancer?

The prognosis for dogs diagnosed with GI cancer is guarded to poor. Factors affecting the dog’s prognosis are related to the cancer and treatment. 

The prognosis is best for dogs with gastrointestinal stromal tumors (GISTs) and certain localized leiomyosarcoma. The cancers have high treatment survival rates and long post-surgical survival periods. 

The worst prognosis is for dogs with gastric adenocarcinoma, which is fatal within days without treatment or within six months with treatment. 

How long can a dog survive with gastrointestinal cancer?

A dog can survive several months with gastrointestinal cancer. The median survival rate varies based on cancer type, stage, and location. 

Gastric adenocarcinoma, the most common GI cancer in dogs, is metastasized at the time of diagnosis in 76% of cases, according to an article “Stomach Tumors in Dogs and Cats” published by the Animal Surgical Center of Michigan.  

Dogs with gastric adenocarcinoma survive for six months after surgery, and dogs with colorectal adenocarcinoma for 22 months. Gastrointestinal stromal tumors have survival rates of up to three years, resulting in a long gastrointestinal disease in dogs life expectancy.

How effective is surgery in treating GI cancer in dogs?

Surgery is relatively effective in treating GI cancer in dogs. The results of the treatment depend on the type and stage of the tumor. 

For example, surgery is curative for dogs with early stages of leiomyosarcoma. Surgery reduces symptoms in dogs with advanced adenocarcinoma. Combining surgery with other options, such as chemotherapy and radiation, improves its effectiveness in some instances. 

What are the treatment options for gastrointestinal cancer in dogs?

The treatment options for gastrointestinal cancer in dogs are listed below. 

• Surgery: Surgical removal is the treatment of choice for most gastrointestinal tumors. The goal is to treat the condition if dealing with a localized tumor or ease the symptoms and keep the dog comfortable until the tumor regrows or the metastases cause issues. A successful surgery requires removing the entire affected area. 
• Chemotherapy: Chemotherapy is used in combination with surgery when the tumor is impossible to remove entirely or alone in the management of alimentary lymphoma. Dogs are much more resistant to chemotherapy and rarely exhibit side effects such as stomach upset and reduced appetite. The incidence of severe complications is under 5%, says a study, “Chemotherapy: Managing Side Effects and Safe Handling,” published in the Canadian Veterinary Journal in 2009. 
• Radiation: Radiation is recommended for localized and inoperable cancers. Vets use high-dose-rate (HDR) brachytherapy, which delivers radiation directly to the affected site. Fatigue and local skin rashes are infrequent side effects of radiation therapy in dogs.   

Can CBD oil help manage symptoms in dogs with gastrointestinal cancer?

Yes, CBD oil can help manage symptoms in dogs with gastrointestinal cancer. Cannabidiol, or CBD, is a non-addictive, non-psychogenic, and health-boosting extract sourced from hemp. 

Dog CBD alleviates pain, inflammation, and nausea while supporting appetite and relaxation. Cannabidiol has a direct anti-tumor effect and boosts the effectiveness of chemo and radiation. 

Discuss the use of CBD oil for dogs with gastrointestinal cancer with a veterinarian to ensure correct use and optimal results. 

Are there preventive measures that can reduce the risk of GI cancer in dogs?

Yes, there are preventative measures that can reduce the risk of GI cancer in dogs. Common recommendations include a balanced diet, minimizing pollutant exposure, regular vet checkups, and genetic testing. 

Provide the dog with high-quality food that is nutritionally rich and balanced for its age and lifestyle. Limit exposure to known carcinogens in the air, food, and environment. Visit the veterinarian for routine exams frequently. Consider genetic testing for dog breeds at a high risk of GI cancer.