As pets age, diseases such as cancer become increasingly common. In fact, it is estimated that almost half of dogs older than 10 years will develop cancer, with a likely similar incidence rate in cats. Although you don’t want to think about your pet developing cancer, arming yourself with information can help you be better prepared. 

Although uncontrolled cell growth can develop in almost any part of a pet’s body, certain cancer types are most common in senior pets. 

Lymphoma in senior pets

Lymphoma causes up to 24% of all cancers in dogs, and is the most common cancer type in cats. This cancer involves lymphocytes, a white blood cell type located in the bloodstream and throughout body tissues, including the lymph nodes, spleen, lungs, bone marrow, and gastrointestinal (GI) tract. This wide distribution of lymphocytes means lymphoma can affect almost any body part, and often multiple locations. In cats, lymphoma most commonly develops in the GI tract, and is often linked to feline leukemia infections.

Since lymphoma can affect so many body parts, the signs can be varied, and include:

• Swollen lymph nodes, which can be palpated under the neck, near the shoulders, around the groin, and behind the knees
• Lethargy
• Decreased appetite
• Weight loss
• Vomiting and diarrhea, particularly in cats

Although lymphoma can be aggressive, cancer typically responds well to treatment, and will often go into remission. If your senior pet develops lymphoma, every day is precious, and treatment may provide months, or years, of valuable time together. 

Mast cell tumors in senior pets

Mast cell tumors (MCTs) are the most common skin tumor in dogs, and can also affect cats. The tumors involve the uncontrolled growth of mast cells, which are white blood cells that function in allergic and inflammatory reactions. MCTs appear as a skin mass, which can be hairless or ulcerated, and are often itchy. The tumors can become red and swollen when handled. 

MCTs are typically surgically removed, and analyzed by a pathologist to determine the tumor’s aggressiveness and spread. Aggressive MCTs are locally invasive and likely to spread, while less aggressive MCTs are typically cured with surgical removal. 

Brain tumors in senior pets

Pets can develop brain tumors anywhere in their brain, or the surrounding tissues. Common primary brain tumor types include:

• Meningiomas
• Choroid plexus papillomas
• Gliomas
• Pituitary adenomas and adenocarcinomas

A brain tumor can also develop if another cancer spreads (i.e., metastasizes) to the brain. 

A growing brain tumor can directly affect the section of the brain involved or put pressure on other brain structures. Brain tumor signs will depend on tumor type and location, and may include:

• Incoordination
• Weakness
• Mentation changes
• Seizures

If your senior pet develops a brain tumor, their prognosis also will depend on the tumor type and location. Some brain tumors can be treated with surgical removal, chemotherapy, or radiation therapy. 

Mammary gland carcinomas in senior pets

Mammary gland tumors develop most commonly in older, intact female dogs, or females who were spayed after several heat cycles. The tumors typically start as a small mass on a pet’s chest or abdomen, but can quickly grow to a large, painful tumor that may become ulcerated. In dogs, approximately 50% of mammary masses are cancerous, and 50% of those spread to the lungs. In cats, approximately 80% of mammary masses are cancerous, with 80% of those spreading to the lungs. Surgical removal can be curative if the mass is removed prior to metastasis; however, lung involvement carries a poor prognosis.

Osteosarcoma in senior pets

Osteosarcoma, or primary bone cancer, which accounts for 95% of all bone tumors in dogs, is highly aggressive, and invades and weakens the bone, causing pain, lameness, and possibly a fracture. In addition to local invasion, osteosarcoma often metastasizes to the lungs and progresses. 

Unfortunately, osteosarcoma carries a poor prognosis. Treatment may include amputation of the affected limb and chemotherapy but rarely offers a cure. Additional treatment is aimed at controlling pain and providing a good quality of life during the pet’s remaining time. 

Melanomas in senior pets

Melanoma is cancer that arises from pigmented cells and occurs most commonly in the oral cavity, nailbed, skin, and eye. Melanoma typically appears as a dark mass, although the lesion may be flat, pink, or mottled. Oral melanoma, which is seen most frequently in breeds with darkly pigmented gums or tongue, is the most common oral cancer in dogs.

Unfortunately, melanoma typically spreads and is often incurable. Treatment may involve surgical removal, chemotherapy, and immune-based therapies.