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Cancer in Dogs: Symptoms, Types, and Treatment

What Are the Most Common Types of Cancer in Dogs?

Lumps and masses in dogs are quite common occurrences, but not all of them turn out to be cancerous. When a mass is determined to be non-cancerous, it is termed as benign. Generally, benign masses tend to grow at a slower pace and do not metastasize to other areas of the body, thus posing minimal health risks.

In contrast, cancerous masses consist of cells that have the ability to proliferate. These are referred to as malignant tumors and can exhibit rapid growth, spreading to various organs and tissues, potentially leading to severe health complications. The rate of cancer growth and its pattern of metastasis depend on the specific type of cancer involved.

Similar to humans, dogs are susceptible to cancer. Approximately 25% of dogs will encounter some form of cancer during their lifetime, with about 50% of dogs over the age of 10 developing the disease. While not an exhaustive compilation, here are some of the more prevalent types of cancers observed in dogs:

  • Anal Sac Adenocarcinoma: This cancer impacts the anal glands, which are scent glands situated in the rectum. It has the potential to metastasize to other regions of the body.
  • Hemangiosarcoma: Originating from blood vessels, this tumor can theoretically manifest anywhere in the body. However, it is commonly found in the heart, liver, or spleen. It is an aggressive cancer often detected after it has already spread.
  • Lymphoma: Dogs can experience various types of lymphoma, with the most common affecting the lymph nodes. While it is prevalent among canine cancers, it is highly responsive to chemotherapy.
  • Mammary Gland Carcinoma: Unspayed female dogs, possessing about five pairs of mammary glands, are more prone to these tumors. Hormones like estrogen and progesterone contribute to mammary development and cancer risk.
  • Mast Cell Tumor: As the most frequent skin cancer in dogs, mast cell tumors can be challenging to diagnose visually due to varying appearances. Prognosis varies from low to high grade, indicating the likelihood of metastasis.
  • Melanoma: These cancers may arise on the skin or in the oral cavity, with oral melanomas typically being malignant and necessitating aggressive treatment such as surgery, radiation, or chemotherapy. Symptoms may resemble dental issues like halitosis and reduced appetite.
  • Osteosarcoma: Among bone cancers in dogs, osteosarcoma is the most prevalent and aggressive, causing significant pain. It frequently affects the limbs of larger dog breeds and often requires surgery followed by chemotherapy or radiation.
  • Transitional Cell Carcinoma: This type of urinary cancer predominantly affects the bladder and often mimics symptoms of a urinary tract infection.


Dogs afflicted with cancer may exhibit various symptoms. Some might present with a noticeable lump or swelling, a persistent wound, enlarged lymph nodes, or unusual bleeding. However, many symptoms are nonspecific and may include:

  • Swelling in the abdomen
  • Behavioral alterations or neurological symptoms like seizures or head tilting
  • Coughing or alterations in breathing patterns
  • Loss of appetite and weight loss
  • Reduced tolerance for exercise
  • Paleness in the gums
  • Lethargy
  • Episodes of vomiting and/or diarrhea

Should you harbor even the slightest concern about your furry companion—especially if you detect behavioral changes or discover a new lump—do not hesitate to schedule an appointment with your veterinarian for a thorough examination.


The causes of cancer in dogs frequently remain elusive and can be affected by a multitude of factors, such as:

  • Age
  • Viral and bacterial infections
  • Exposure to chemicals and toxins
  • Genetic predisposition
  • DNA mutations
  • Damage from UV radiation or other environmental stimuli

What Does a Cancerous Lump Look Like on a Dog?

Cancerous lumps cannot be distinguished visually from benign, non-cancerous lumps, so attempting to self-diagnose at home is not advisable. Lumps vary in their characteristics, including size, shape, and texture; some may feel firm and fixed, while others may feel soft and flexible. They may exhibit features such as hairlessness, pigmentation, or ulceration, and their sensitivity to touch can vary.

It’s crucial to distinguish lumps from lymph nodes, as dogs have multiple pairs of lymph nodes located in various regions of their body, including underneath the jaw, in front of the shoulders, under the armpits, and behind the knees. Lymph nodes typically present as small, oval-shaped, painless swellings beneath the skin. Enlarged lymph nodes can signify a potential symptom of cancer.

Should you discover a new lump or bump on your dog, it’s important to schedule an appointment with your veterinarian for an accurate diagnosis and appropriate management.


To diagnose cancer in dogs, veterinarians employ various methods:

  • Physical Examination: Veterinarians conduct a thorough physical examination to detect any abnormal or unexplained lumps, bruises, or masses that are palpable (able to be felt by pressing on the body’s surface).
  • Fine-Needle Aspiration (FNA): A sample of the tumor is collected via FNA and sent for analysis to determine its nature.
  • Biopsy: In some cases, a biopsy is performed to obtain a larger sample of the tumor, usually under sedation or anesthesia. The sample is then analyzed to identify the type, malignancy, and grade of the cancer, offering insights into its potential aggressiveness.
  • Bloodwork and Urine Testing: These tests are conducted to identify any abnormalities that may help narrow down the issue to a specific organ or body system.
  • Imaging: Radiographs or ultrasound may be recommended to screen for masses in the chest or abdomen, aiding in the diagnostic process.

Once a diagnosis is made, veterinarians may suggest further testing or refer the case to an oncologist for additional evaluation and treatment, which may include staging to determine the extent of cancer spread. Additional tests such as CT scans, bone marrow aspirates, or biopsies may be performed.

The prognosis varies based on the type of cancer, influenced by its grade and stage. Generally, a higher grade and stage indicate a poorer prognosis.


In general, there are three primary options for treating cancer in dogs: surgery, radiation therapy, and chemotherapy. The effectiveness of each treatment method varies depending on the type and stage of the cancer. Often, a combination of treatments may be necessary to achieve the best possible outcome. While a complete cure is challenging to achieve, these treatments can help manage the disease and improve the dog’s quality of life.

Common chemotherapy medications used in treating cancer in dogs include:

  • Carboplatin
  • Chlorambucil
  • Cyclophosphamide
  • Doxorubicin
  • L-asparaginase
  • Lomustine
  • Mitoxantrone
  • Palladia
  • Prednisone
  • Vinblastine
  • Vincristine

Treatment and Management

Treating and managing cancer in dogs involves distinct approaches from those used in humans, with differing goals and expectations. The primary aim is to sustain a good quality of life, often achieved through lower drug dosages and less frequent administration compared to human treatments, thereby minimizing potential side effects. Common side effects in dogs include decreased appetite, lethargy, vomiting, or diarrhea, with more severe complications like bone marrow suppression and infections also possible. With few exceptions by breed, dogs typically do not experience hair loss during chemotherapy.

During chemotherapy, it’s crucial to ensure your dog’s comfort and effectively manage any pain they may experience. This necessitates a strong partnership with your veterinarian, adherence to recommended appointments, and diligent monitoring through bloodwork and other tests. Caring for a dog with cancer can be emotionally taxing and burdensome, but it’s important to cherish each day’s opportunities for play, bonding, and affection.

Deciding when to cease treatment or consider euthanasia is a deeply personal and variable process for both pets and their owners. Numerous factors such as prognosis, metastasis, treatment risks, costs, and quality of life come into play. However, the evaluation of quality of life, though subjective, can be guided by the principles of the 5 Freedoms:

  • Freedom from hunger and thirst
  • Freedom from discomfort
  • Freedom from pain, injury, and disease
  • Freedom to express normal behavior
  • Freedom from fear and distress

Your veterinarian serves as an invaluable resource in determining the appropriate time for such decisions. They possess expertise in end-of-life care and disease outcomes, with access to various resources and tools to aid in navigating this challenging process.

Reducing Cancer Risks in Dogs

Regrettably, there is limited action a pet owner can take to entirely prevent most cancers in dogs. However, regular checkups and prompt evaluation of any new lumps or unexplained illnesses should prompt an immediate visit to the veterinarian. Minimizing sun and UV exposure, opting for spaying/neutering, and for breeds prone to specific tumors, more frequent screenings are advised.

Cancer in Dogs FAQs

How frequently should dogs be examined for lumps and bumps?

Dogs should undergo an annual examination with your veterinarian, with senior dogs requiring more frequent visits as necessary, particularly if managing an underlying condition. Mast cell tumors have the potential to develop rapidly and change in size quickly, emphasizing the importance of scheduling an appointment promptly upon discovering any new lumps or bumps.

What distinguishes a mass from a tumor in a dog?

Generally, the terms “tumor” and “mass” are used interchangeably. It’s essential to recognize that neither term consistently implies cancer, as some tumors can be benign, and some masses may result from injury or infection (abscess).

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