The Cancer Lump Test – Is Your Dog’s Lump Hard or Soft?


Cancerous lumps, also known as tumors or neoplasms, are abnormal masses of tissue that form when cells divide and grow uncontrollably. They can be benign (non-cancerous) or malignant (cancerous). Cancerous lumps in dogs are a serious health concern, as cancer is a leading cause of death in dogs. According to research, the lifetime prevalence of malignant tumors in dogs is around 30 per 1000 dogs (Schwartz, 2022). Understanding the characteristics of cancerous lumps, like their appearance and texture, is important for early detection and prompt veterinary care.

This article provides an overview of the different types of cancerous lumps in dogs, their typical appearance and location, causes and risk factors, how they are diagnosed, treatment options, prognosis, and steps pet owners can take to prevent cancer in dogs. The goal is to inform dog owners about this common canine health problem so they know what signs to look out for and when to seek veterinary advice if they find a concerning lump on their pet.

Types of Cancerous Lumps

Some of the most common types of cancerous lumps that can develop on dogs include:

Mast cell tumors – These lumps form from mast cells in the skin, connective tissue, and immune system. Mast cell tumors often look like raised bumps on the skin that may be red, ulcerated, or swollen. They can develop anywhere on the body and may release histamine, causing itchiness. According to Knutsford Vet Surgery, mast cell tumors account for about 20% of skin tumors in dogs [1].

Lipomas – While most lipomas are benign fatty tumors, some can develop into a cancer called liposarcoma. Liposarcomas are invasive tumors that may look similar to lipomas at first. They tend to grow rapidly and can spread to other areas of the body.

Sebaceous adenomas – These lumps arise from sebaceous glands in the skin. They often appear as hairless bumps and may ulcerate or bleed. Sebaceous adenomas have the potential to become malignant.

Histiocytomas – Histiocytomas are generally benign tumors of histiocytes, a type of white blood cell. They usually look like raised, hairless bumps on the skin that may ulcerate. While rare, histiocytomas can sometimes progress to histiocytic sarcomas, which are malignant cancers.


Cancerous lumps on dogs can vary greatly in their appearance. Some key things to look for include:

a close up photo of a cancerous lump on a dog

  • Size – Cancerous lumps tend to grow quickly and can become very large, sometimes within just a few weeks. They may start out small but then rapidly increase in size.
  • Shape – Cancerous lumps are often irregularly shaped. They do not have smooth, round, or symmetrical borders.
  • Color – The color of the lump can range from pink to red to dark purple or black. Lumps that are abnormal colors like these warrant investigation.
  • Texture – Cancerous lumps usually feel firm or hard. They are generally solid masses rather than fluid-filled pockets under the skin. The surface may look ulcerated or like cauliflower.
  • Hardness/Softness – While some benign fatty tumors can feel soft, cancerous lumps tend to be much harder in texture. They are solid or firm masses that feel immovable under the skin and do not fluctuate in size.

In general, lumps that are rapidly growing, abnormally shaped or colored, ulcerated, and hard or immovable should raise red flags for potential cancer. Any new lumps on a dog that do not go away within a couple weeks should be evaluated by a veterinarian as soon as possible.


Cancerous lumps on dogs can appear in various locations, but some of the most common areas include:

Mammary Glands: One of the most common locations for cancerous lumps in female dogs is the mammary glands or breasts. Mammary tumors account for around 50-70% of all tumors found in female dogs that have not been spayed. These lumps usually form under or around the nipples.

Skin: The skin is another common site for lumps in dogs. Mast cell tumors, which are a type of skin cancer, represent approximately 20% of all skin tumors found in dogs. They can develop anywhere on the skin surface. Other common skin tumors like lipomas may not be cancerous but can still form lumps.

Mouth: Oral melanoma is a type of cancer that causes lumps and bumps to form in a dog’s mouth, including on the gums, tongue, lips and roof of the mouth. It accounts for up to 7% of all malignant tumors found in dogs.


There are several potential causes of cancerous lumps in dogs, including genetics, environmental factors, and viruses.

Genetics play a key role, as some dog breeds are predisposed to developing certain types of cancer. For example, Boxers are prone to mast cell tumors, while Golden Retrievers have a higher risk for lymphoma and hemangiosarcoma. Genetics make some dogs more vulnerable to the effects of carcinogens in the environment.1

Environmental factors like exposure to pesticides, second-hand smoke, pollution, and sunlight can damage cells and potentially lead to cancer over time. Carcinogens in the surroundings can initiate or accelerate the development of tumors and growths.

Oncogenic viruses are responsible for around 15% of dog cancers. Papillomaviruses can prompt squamous cell carcinoma, while retroviruses are linked to hematopoietic cancers like leukemia. These viruses insert their DNA into the dog’s cells, promoting abnormal and uncontrolled growth.

a dog receiving chemotherapy treatment

Risk Factors

There are several factors that can increase a dog’s risk of developing cancerous lumps:

Age: Older dogs are more prone to cancer. According to the Merck Veterinary Manual, over 50% of cancers occur in dogs older than 10 years.[1]

Breed: Some breeds are genetically predisposed to certain cancers. For example, Boxers are prone to mast cell tumors while Golden Retrievers have a high incidence of lymphoma and hemangiosarcoma.[1]

Obesity: Overweight dogs have an increased risk for some cancers like mammary gland tumors. Maintaining an optimal body weight can help reduce cancer risk.[2]

Sun exposure: Dogs with light skin and short hair coats may be prone to sun-induced skin cancers if not protected from extended UV light exposure.[3]

Environmental factors: Exposure to things like pesticides, herbicides, and secondhand smoke can potentially increase cancer risk in dogs.[3]


The initial diagnostic steps for detecting cancerous lumps in dogs involve a thorough physical exam by a veterinarian. The vet will inspect and palpate all over the dog’s body to locate any abnormal lumps or masses. They will note the size, shape, texture, mobility, and location of any findings. According to the Lombard Veterinary Hospital, some masses feel soft and movable under the skin, while others feel very firm or attached to underlying tissues.

If the vet discovers any suspicious lumps, the next step is to take samples for biopsy. This involves using a needle to extract cells from the mass (fine needle aspiration) or surgically removing a small piece of the lump (biopsy). These samples are then examined under a microscope by a veterinary pathologist to determine if cancer is present and identify the tumor type. Imaging tests like x-rays, CT scans, or ultrasound may also be used to evaluate the size and extent of tumors.

a biopsy sample being examined under a microscope

As per Countryside Veterinary Clinic, early detection and diagnosis is key for effectively treating cancer in dogs. They advise pet owners to routinely check their dog’s body for any new lumps or bumps and to contact their vet promptly if any are found. Catching cancer early greatly improves prognosis and survival rates.


There are several main treatment options for cancerous lumps in dogs, including surgery, chemotherapy, radiation therapy, immunotherapy, and palliative care.1

Surgery is often the first line of treatment and the most effective option for removing accessible tumors. The goal is to fully remove the cancerous cells and prevent further spread. In some cases, multiple surgeries may be required if the cancer recurs.2

Chemotherapy uses anti-cancer drugs to kill cancer cells and shrink tumors. It may be used before surgery to make the tumor smaller and easier to remove. Or it can be used after surgery to kill any remaining cancer cells. Chemotherapy protocols vary based on the type and stage of cancer.3

Radiation therapy uses high-energy radiation to kill cancer cells and shrink tumors. It may be used alone or with chemotherapy and surgery. Side effects can include skin irritation and hair loss in the treated area.

Immunotherapy stimulates the dog’s immune system to attack cancer cells. Certain vaccines, medications, and cellular therapies show promise in treating canine cancers.

Palliative care focuses on relieving pain and discomfort when a cure is not possible. This may include medications, nutritional support, physical therapy, and other therapies to improve quality of life.


The prognosis for canine cancer patients depends significantly on the type and location of the cancer as well as how early it is detected and the treatment pursued. According to the CSU Animal Cancer Center, cancers such as lymphoma, osteosarcoma, and mast cell tumors tend to be more aggressive and have poorer prognoses.1 The prognosis is generally better if the cancer is detected early before it has spread to other parts of the body. Surgical removal of localized tumors and masses can be curative if caught early enough. Dogs receiving chemotherapy or radiation for certain cancers like lymphoma may achieve remission for 6 months to 2 years on average.

Overall, with treatment the average survival time for dogs after a cancer diagnosis ranges from 6 months up to 2 years depending on the type and stage of cancer at diagnosis. Certain cancers like mast cell tumors and soft tissue sarcomas have better prognoses with 1-2 year survival times on average with appropriate treatment. More aggressive cancers like hemangiosarcoma and osteosarcoma tend to have survival times of only 2-6 months even with treatment.2 Pursuing early screening, detection and treatment is key to improving prognosis.


a dog being neutered by a veterinarian

There are some steps dog owners can take to help prevent cancer in their pets. One of the most important is spaying or neutering dogs when they are young, preferably before 6 months of age. Neutering greatly reduces the risk of mammary tumors in female dogs, and neutering male dogs eliminates the risk of testicular cancer (AKC). Maintaining a healthy weight through proper diet and exercise is also key, as obesity has been linked to increased cancer risk in dogs. Owners should avoid exposing their dogs to known carcinogens like secondhand smoke, pesticides, herbicides, and other hazardous chemicals whenever possible.

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