Discovering a lump or bump on your furry loved one can be a heartstopping moment. Most pet owners’ minds go immediately to cancer, but that is not always the case. Cysts, lipomas, and allergic reactions can also pop up on your pet, and scare you, but a thorough diagnostic workup at Homestead Animal Hospital is needed to determine whether your pet’s mass is truly cancerous. If the tests indicate a cancer diagnosis, your beloved companion may have one of these five most common cancers in pets. 

#1: Mast cell tumor

Mast cell tumors are the most common skin tumor in dogs, and the second-most common skin tumor in cats. These tumors are lumps full of histamine, which is a compound responsible for inflammation and swelling of the surrounding tissue. Since the tumor size is dependent on the amount of histamine that leaches out, the mass can vary from day to day. 

  • Signs — Clinical signs will vary, based on the mast cell tumor’s grade. Pets can display small masses in the skin with minimal inflammation, or they can develop large, ulcerated, and hairless tumors that are more likely to be aggressive.
  • Risk factors — Boxers and Boston terriers are the most commonly affected dog breeds predisposed to developing mast cell tumors, making up roughly 50% of all cases. Other breeds include pugs, cocker spaniels, bullmastiffs, Labrador retrievers, golden retrievers, Staffordshire terriers, and schnauzers. In cats, the Siamese are most at risk for mast cell tumors.

#2: Osteosarcoma

Osteosarcoma is the most common bone tumor in pets, making up 95% of all bone-tumor cases. Other bone tumors include chondrosarcoma, fibrosarcoma, and hemangiosarcoma. The majority of osteosarcoma tumors develop spontaneously, with no known or apparent cause. Osteosarcoma in dogs tends to be highly aggressive, and can metastasize rapidly to the lungs. 

  • Signs — Lameness and swelling of the affected bone are the most common signs of osteosarcoma, while pathologic fractures can occur at the tumor site, if the bone is weakened enough.
  • Risk factors — Scottish deerhounds are most at risk for developing osteosarcoma, but all large- and giant-breed dogs have an increased risk, particularly tall dogs. Older dogs are most commonly affected, although osteosarcoma can also develop in young dogs. Osteosarcoma is uncommon in cats, yet is the most common feline bone tumor. Osteosarcoma is less aggressive in cats than dogs, and up to a third of feline bone tumors are benign.

#3: Lymphoma

Lymphoma is a cancer of a type of white blood cells called lymphocytes, but is not restricted to the blood, and may originate in the lymph nodes, spleen, liver, bone marrow, and gastrointestinal tract—virtually anywhere in the body. In cats, lymphoma generally attacks the gastrointestinal tract. Lymphoma is aggressive if untreated, but often responds well to treatment, which can offer affected pets a good quality of life for months after diagnosis. 

  • Signs — Generalized, swollen lymph nodes under the jaw, near the shoulders, or behind the knees are the most common lymphoma signs, as well as decreased appetite, lethargy, and weight loss. Other signs are specific to the affected organs.
  • Risk factors — While any pet can develop lymphoma, some breeds are more predisposed to lymphoma, with boxers, golden retrievers, Scottish terriers, basset hounds, and bulldogs most at risk. In cats, lymphoma is associated with feline leukemia, which makes vaccination an important prevention tool.

#4: Squamous cell carcinoma

Squamous cell carcinoma originates from squamous cells in the skin, and tends to cause local disease, rarely metastasizing to other body areas. This cancer type can also appear orally, and is much more locally aggressive.

  • Signs — Squamous cell carcinoma lesions initially appear as a scab or red, thickened area, but can progress to skin ulcerations. Some tumors look like a mass, while others will appear as a flat, red, plaque-like lesion. Oral squamous cell carcinoma can create a tumor anywhere in the mouth, such as on the tonsils or gums, but often appears under the tongue, and frequently attacks the jawbone.
  • Risk factors — Squamous cell carcinoma can affect any pet, but white or light-colored pets who spend ample time in the sun are most at risk. Pets exposed to carcinogens, such as tobacco smoke, also have a higher risk of squamous cell carcinoma development.

#5: Mammary cancer

Mammary cancer is typically considered a female-only disease, but can affect male cats and dogs, although females have a much higher risk. In female dogs, 50% of mammary tumors are malignant, but few are fatal. On the other hand, more than 85% of mammary tumors in cats are malignant, and most are aggressive and metastasize. 

  • Signs — The most common mammary cancer sign is a palpable mass under the skin along the mammary chain. Discharge from the mammary gland, skin ulceration over the gland, painful or swollen glands, loss of appetite, weight loss, and weakness are other frequent mammary cancer signs.
  • Risk factors: Poodles, dachshunds, and spaniels are the dogs most affected with mammary cancer, particularly if they become obese at a young age. The risk of a dog developing a mammary tumor is 0.5% if spayed before their first heat cycle, which usually occurs in most breeds between 6 and 8 months of age. After the first heat, the risk increases to 8%, and then to 26% after the second heat.

In cats, Siamese, oriental breeds and domestic shorthairs are most at risk. Cats spayed at any point have a 40% to 60% reduced mammary tumor risk, and before 6 months of age, have a greatly reduced risk, as much as 7 times. 

If you notice an odd lump while massaging your pet, call us to schedule an appointment. The sooner we identify the mass, the better prognosis for your best friend.