Tumors in Dogs | Types, Symptoms, and Treatment

Tumors are a fairly common condition in dogs, especially from around 10 years of age onward.

Although when we hear the word "tumor" our mind automatically jumps to cancer, we should know that tumors can be benign or malignant, so a tumor showing up doesn't necessarily mean our dog is going to develop cancer.

Although there are many types of tumors, in this article we'll explain the characteristics of the ones that most commonly affect dogs. Shall we get started?

What is a tumor, and what types of tumors occur in dogs?

A tumor is an uncontrolled multiplication of cells in a tissue, which build up, usually forming a mass that can sometimes be felt. Depending on their growth pattern and ability to invade nearby tissue, tumors are classified as benign or malignant.

If the tumor is benign, the cells multiply in an uncontrolled way but don't spread to other parts of the body. If the tumor is malignant (cancer), on the other hand, the cells that make it up can spread to other areas of the body and grow in other nearby organs. This spread is what's known as metastasis.

Benign tumors usually don't need treatment unless they cause the dog discomfort, or press on some organ due to their size, and only need periodic monitoring to make sure they don't grow or change in appearance. Malignant tumors, or cancer, need to be treated as soon as possible, generally through surgical removal.

Is it common for dogs to develop cancer?

Cancer is a fairly common disease, especially in dogs over 10 years old. Around 50% of dogs over 10 develop cancer at some point in their life. And, although cancer is the most common cause of death in older dogs, we should know that half of cancers are curable if caught in time.

What symptoms does cancer cause?

Cancer symptoms are similar to those seen in people. A lump or bump appearing, sores that won't heal, enlarged lymph nodes, limping or bone swelling, abnormal bleeding, weight loss, among others.

These are classic cancer symptoms, but sometimes dogs show no signs at all, at least at first. Because of this, it's very important to see the vet as soon as possible whenever we notice something unusual in our dog.

Treatments available for cancer

In dogs, there are various treatment options similar to those available for people. Surgical removal tends to be the most common option, followed by chemotherapy and radiotherapy, and immunotherapy techniques (similar to vaccines) that stimulate the immune system to fight cancer are currently being developed.

What are the most common tumors in dogs?

The cancers most commonly diagnosed in dogs are mast cell tumors of the skin, lymphoma in the lymph nodes, mammary gland tumors, soft tissue sarcoma, and bone cancer.

As for benign tumors, the most common ones found in dogs are lipomas and skin histiocytomas.

Mast cell tumor

The mast cell tumor is one of the most common types of skin cancer in dogs. It appears as a mass on the skin that grows quickly and is generally reddish-looking and itchy. This is because it contains histamine, a substance linked to the itching symptoms seen in allergies.

Flat-faced breeds such as the Boxer, Pug, or French Bulldog are the dogs most prone to this type of tumor, and it's more common in older dogs.

This type of tumor is diagnosed by taking a sample of the mass through a needle aspiration for cytology. Once the diagnosis is confirmed, since it's a malignant tumor, it needs to be surgically removed, and its aggressiveness determined through biopsy analysis to see whether any additional treatment is needed.

Lymphoma

Lymphoma is a type of cancer that affects the lymphatic system. In dogs it causes loss of appetite, lethargy, and enlarged lymph nodes. It's diagnosed through a needle aspiration of the nodes or a biopsy. The most common treatment for it is chemotherapy.

Mammary gland tumor

Mammary tumors are very common in female dogs, which is why spaying is recommended after their first heat, since this greatly reduces the chances of developing this type of cancer.

This type of tumor is usually detected by feeling for masses developing in the mammary glands. It commonly metastasizes to the lungs, seriously worsening the situation. Because of this, we should see a vet if we notice any lumps in our female dog's mammary glands.

Treatment involves surgical removal of the tumors, along with spaying the animal.

Hemangiosarcoma

Hemangiosarcoma is a type of cancer of the blood cells, so it commonly develops in the spleen, since it's an organ with a rich blood supply. It can also develop in the heart and skin.

It's usually diagnosed during a routine abdominal ultrasound, or because it causes a splenic rupture. The spleen is surgically removed and the diagnosis is confirmed by analyzing the tissue. Treatment then continues with chemotherapy, since metastasis is common with this type of cancer.

Osteosarcoma

Osteosarcoma is a type of cancer that affects the bones, especially the limbs of large and giant breed dogs. This condition causes limping in the dog and is diagnosed via X-ray. A biopsy is sometimes needed, since the radiographic signs can look similar to other conditions such as arthritis.

Once diagnosis is confirmed, treatment usually consists of amputating the affected limb, followed by chemotherapy. In some cases, only the affected part of the bone can be removed.

Histiocytoma

Like the mast cell tumor, the histiocytoma is a skin tumor, but this one is considered benign. It appears as a small lump on the skin and usually resolves on its own within 2 to 3 months. Removal is only recommended in cases where it bothers the dog.

It's the most common tumor in young dogs under 3 years old, and especially in English Bulldogs, Boxers, Boston Terriers, Shar Peis, and Scottish Terriers.

Lipoma

Lipomas are the most common tumors in dogs. They appear as fatty masses under the skin, which can be located anywhere on the body. They're considered benign tumors and rarely cause the dog pain.

Diagnosis is confirmed through needle aspiration of the contents, and they aren't removed unless they bother the dog.

What is the cure rate for cancer in dogs?

Generally speaking, for malignant tumors we're talking about a 60% survival rate. Many lumps or masses, if removed in time, give patients a very good long-term prognosis.

However, if the cancer goes untreated, we'd be talking about a survival time of months.

What's more, the prognosis is directly tied to how early the diagnosis is made, so whenever we notice anything that makes us suspect something's wrong with our dog, we should see a vet.