Mammary Cancer in Cats: Why Early Spaying Matters and What to Do

By Tailwisp Editorial TeamUpdated October 20, 20264 min read

Cats are masters at hiding lumps under their fur. Mammary cancer is the third most common cancer in cats, and unlike in many other conditions, there is a straightforward way to cut the risk: spay young. For cats that are already older or unspayed, regular checks can catch problems early.

Mammary glands in cats

A female cat has eight mammary glands, in two rows along the belly. They enlarge in pregnancy and nursing. Tumors can develop in any gland, and may affect more than one. Unlike in dogs, where many mammary tumors are benign, the majority in cats, around 80 to 90 percent, are malignant adenocarcinomas, which can spread to lymph nodes and lungs.

Risk factors

• Being unspayed. Hormones such as estrogen and progesterone play a role. Cats spayed before six months have a greatly lower risk, and the risk climbs for each heat cycle they go through. See when to spay or neuter a kitten.
• Age. Most cases occur in cats over ten years old.
• Breed. Siamese cats appear to be at higher risk.
• Hormone treatments, such as progestin injections, which are linked with benign hyperplasia and tumors.

Signs

• A firm lump or several lumps under the belly skin, near the nipples.
• Swelling, redness or ulcers on the skin over the lump.
• Discharge from a nipple, sometimes bloody.
• Licking at the area.
• Pain or reluctance to be touched.
• Swollen lymph nodes, in the groin or armpit.
• Weight loss, cough or breathing trouble, if spread to the lungs. See cat panting and open-mouth breathing.

Not every lump is cancer, since benign hyperplasia and infection can cause swelling, but only a vet can tell.

How to check at home

Once a month, when your cat is relaxed, gently run your fingertips along both rows of the mammary glands, from the chest to the groin. Normal glands feel flat and soft. Report any lump, however small. Make a note, and take a photo of the area. Early detection matters.

Diagnosis

The vet palpates the lump and lymph nodes, takes a needle sample or biopsy, and may remove the lump to send for examination. Bloodwork, chest X-rays and abdominal ultrasound check for spread. See cat blood tests explained.

Treatment

• Surgery. The main treatment, often a radical mastectomy, which removes the affected glands, and sometimes the whole chain on one or both sides. More extensive surgery lowers the chance of regrowth. Cats usually cope well, and are given pain relief and a recovery plan. See cat anesthesia safety.
• Chemotherapy. May be recommended after surgery, particularly for larger or higher-grade tumors, to delay spread.
• Spaying, at the time of surgery, if the cat is not spayed.
• Supportive care.

Outlook

Outcomes depend on the tumor size, grade and spread. Cats with small tumors, less than about 2 centimeters, removed early, may live years, while larger tumors carry a worse outlook. Regular rechecks look for local regrowth and spread. Your vet will discuss prognosis once the tumor is examined.

Prevention

The most effective prevention is to spay female cats before their first heat, around five to six months of age or as your vet advises. Avoid hormone injections. Check your cat regularly. See cancer in cats.

Adopted adults

If you adopt an unspayed adult female, ask your vet about spaying, and examine her belly. Even older cats benefit from spaying, though the risk reduction is smaller.

Supporting your cat after surgery

• Keep her indoors, warm and quiet.
• Use a cone, or a soft recovery suit, to prevent licking.
• Give pain relief as directed.
• Check the incision daily.
• Return for suture removal and follow-up.

See caring for a cat after spay or neuter.

Making treatment decisions

Surgery for mammary cancer is major, and recovery takes time. Ask your vet about the extent of surgery, the likelihood of regrowth, chemotherapy options and the cost. In an older cat with other illness, the plan may be adjusted. Discuss quality of life, and what outcomes to expect. If you are unsure, ask for an oncology referral.

Benign lumps and other swellings

Not every lump is cancer. Mammary hyperplasia occurs in young cats, usually after heat or hormone treatment, and causes enlarged glands. Mastitis, an infection of the gland, may occur in nursing cats. Abscesses and other skin lumps also appear on the belly. Only a sample under the microscope can tell, so do not wait.

Follow-up after surgery

After surgery, your vet will check the wound, lymph nodes and chest. X-rays may be repeated every few months to look for spread. Monthly belly checks continue. If a new lump appears, report it immediately. Early action can still help.

When to see a vet

See a vet promptly for any lump on your cat's belly. Use the US vet directory to find a clinic.

This article is general educational information, not veterinary advice. Every cat is different. If your cat is unwell, or you are unsure about a symptom, diet change or medication, contact your veterinarian.