A Compassionate Guide to the 7 Most Common Cancers in Cats

Our feline friends are masters at hiding illness, which can make diagnosing diseases like cancer a challenge. At Harmony Pet Clinic, we are committed to helping cat owners in Tomball, Spring, and surrounding communities understand the subtle signs of feline cancer. This guide provides essential information on the seven most common cancers in cats to empower you in safeguarding your cat’s health.

1. Lymphoma (Cancer of the Lymphatic System)

Similar to dogs, lymphoma is the most common cancer diagnosed in cats. It targets the lymphatic system, a vital part of the immune defense. In cats, it frequently affects the gastrointestinal (GI) tract, but can also appear in the lymph nodes, chest, or nasal cavity.

Signs to Watch For:

• Digestive Issues (for GI lymphoma): Chronic vomiting, diarrhea, loss of appetite, and significant weight loss.
• Respiratory Distress: Coughing or difficulty breathing if the cancer is in the chest.
• Swollen lymph nodes (less common as a primary sign than in dogs).
• General lethargy and hiding more than usual.

Causes & Treatment:

Historically, Feline Leukemia Virus (FeLV) was a primary cause, but with widespread vaccination, this is less common. Now, it often develops in older, FeLV-negative cats. Chemotherapy is the cornerstone of treatment and is often very effective, leading to remission and a good quality of life. The specific protocol depends on the type and location of the lymphoma.

2. Squamous Cell Carcinoma (SCC)

Squamous Cell Carcinoma is a type of skin cancer that also commonly occurs in the mouth. On the skin, it is strongly linked to sun exposure, typically affecting white or light-colored cats on their ears, eyelids, and nose. Oral SCC is aggressive and locally invasive.

Signs to Watch For:

• Skin: Persistent, non-healing sores or scabs, often on the ear tips or face.
• Oral: Drooling, difficulty eating (dropping food), bad breath, facial swelling, or visible mass in the mouth.

Causes & Treatment:

Sun exposure is a major cause for skin SCC. The cause of oral SCC is less clear. Treatment for skin SCC involves surgical removal, cryosurgery (freezing), or radiation. For oral SCC, treatment is more challenging due to the location. It may involve aggressive surgery, radiation, and/or chemotherapy, with a focus on maintaining quality of life.

3. Fibrosarcoma (Tumor of Connective Tissue)

Fibrosarcoma is an aggressive tumor that develops from the fibrous connective tissues of the skin and subtissues. It is known for being locally invasive, growing quickly and sending out “fingers” of cancerous tissue that can make complete removal difficult.

Signs to Watch For:

• A firm, often irregular lump under the skin.
• The mass is typically attached to the underlying tissues and is not easily moved.
• Rapid growth of the lump.

Causes & Treatment:

While any inflammation can potentially trigger this cancer, it has been notably associated with injection sites (called injection-site sarcoma), though this is rare. The primary treatment is aggressive surgical removal with very wide margins. Due to its invasive nature, surgery is often followed by radiation therapy to eliminate any remaining cancer cells.

4. Mammary Gland Carcinoma (Breast Cancer)

Mammary tumors are very common in cats. Unfortunately, unlike in dogs where 50% are benign, about 85-90% of mammary tumors in cats are malignant (cancerous) and tend to spread quickly to the lymph nodes and lungs.

Signs to Watch For:

• One or more lumps or swellings along the cat’s belly/chest area (the mammary chains).
• The lump may be small like a pea or much larger.
• The tumor may be ulcerated or bleed.

Causes & Treatment:

Hormones play a key role. Spaying a cat before her first heat cycle reduces the risk by over 90%. Treatment involves radical surgical removal of the entire affected mammary chain. Chemotherapy is often recommended after surgery to help prevent or slow metastasis.

5. Mast Cell Tumors

While also seen in dogs, mast cell tumors in cats behave differently. They most commonly appear in two forms: a skin form, which is often benign, and an internal (visceral) form that typically affects the spleen or intestines and is much more aggressive.

Signs to Watch For:

• Skin: Small, firm, raised, hairless bumps, often on the head and neck.
• Visceral: Vomiting, poor appetite, and weight loss due to an enlarged spleen or intestinal mass.

Causes & Treatment:

The cause is unknown, though Siamese cats may be predisposed. Benign skin tumors can often be cured with surgical removal alone. The aggressive visceral form requires surgery (often removal of the spleen) followed by chemotherapy.

6. Osteosarcoma (Bone Cancer)

Though less common in cats than in dogs, osteosarcoma is a serious bone cancer that can affect cats of any age. It is an aggressive tumor that destroys bone tissue and can metastasize to other parts of the body, most notably the lungs.

Signs to Watch For:

• Limping or lameness that does not resolve.
• A firm, noticeable swelling on a leg, the skull, or ribs.
• Reluctance to jump or move, and signs of pain when touched.

Causes & Treatment:

The cause is unknown. Unlike in dogs, it doesn’t seem to be linked to size. Treatment typically involves amputation of the affected limb to remove the painful tumor, which can significantly improve quality of life. In cats, metastasis is less rapid than in dogs, so amputation alone can sometimes be curative. Chemotherapy may be discussed depending on the case.

7. Transitional Cell Carcinoma (Bladder Cancer)

Transitional Cell Carcinoma (TCC) is a cancer of the cells lining the urinary bladder. It can mimic the signs of a urinary tract infection (UTI) or bladder stones, which can sometimes delay diagnosis. It is an invasive cancer that can cause significant urinary obstruction.

Signs to Watch For:

• Straining to urinate or urinating in frequent, small amounts.
• Blood in the urine (hematuria).
• Inappropriate urination outside the litter box.
• Lethargy and loss of appetite as the disease progresses.

Causes & Treatment:

The exact cause is unknown. Due to its location, surgical removal is often not possible. Treatment is typically focused on medical management to improve quality of life. This includes anti-inflammatory drugs (like piroxicam) and sometimes targeted chemotherapy. These treatments can help shrink the tumor and alleviate symptoms for a period of time.