Home › Animalia › Animal health › Animal diseases › Breast tumors of the cat
Breast tumors of the cat
Mammary tumors are among the most common cancers of the cat. Unlike the female dog, in whom many of these tumors are benign, they are malignant in the vast majority of cases in the cat. They appear as one or more lumps along the mammary cha...
What is it?
Mammary tumors are among the most common cancers of the cat. Unlike the female dog, in whom many of these tumors are benign, they are malignant in the vast majority of cases in the cat.
They appear as one or more lumps along the mammary chains, under the belly.
Two messages are important here: these tumors spread quickly, so a lump under the belly of a cat shows itself without delay; and early sterilization greatly reduces the risk of them appearing.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
One or more firm lumps along the udders, under the belly, often discovered by chance while petting the animal.
They are initially small and painless, sometimes the size of a grain of rice.
Several udders are frequently affected at the same time, on one or both chains.
Over time, the masses enlarge, adhere to the skin, ulcerate, ooze and bleed; they then become painful.
Swelling of a hind limb or lower abdomen when lymphatic circulation is blocked.
Swollen lymph nodes in the groin or armpit.
Weight loss, depression, rapid or difficult breathing when the disease has reached the lungs.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
These tumors arise from cells in the mammary glands, whose multiplication becomes uncontrolled.
Sex hormones play a central role: repeated exposure to hormones during successive heats promotes their appearance.
Hormonal treatments intended to block heat, still used in some homes, clearly increase the risk and can also cause benign breast lumps.
A predisposition exists in certain lines, notably Siamese type cats.
Cat not sterilized, or sterilized late.
Use of hormonal treatments to prevent heat.
Age: the disease mainly affects middle-aged to older cats, and the risk increases with age.
Certain Oriental and Siamese lines seem more concerned.
Males can be affected, but it is rare.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
Palpate your cat's belly regularly: these tumors are accessible by hand and early discovery changes a lot of things.
The veterinarian examines all of the udders, on both chains, measures each mass and palpates the lymph nodes in the groin and armpit.
Chest x-rays are taken before any decision: the lungs are the first destination for these tumors, and their condition determines the strategy.
An ultrasound of the abdomen looks for damage to deep lymph nodes and organs.
A blood test assesses the general condition and prepares for anesthesia.
Laboratory analysis of the removed tumor specifies its nature and aggressiveness: it is this analysis which guides the rest of the treatment.
Treatment
Surgery is the basic treatment and it must be broad. In the cat, the removal of the entire mammary chain from the affected side is the rule, and not the removal of the lump alone: the tumor cells circulate along the chain.
Neighboring lymph nodes are removed when they are affected or suspected.
When both chains are involved, the procedure is often carried out in two stages to allow the skin to close.
Chemotherapy is frequently offered after surgery because these tumors spread early.
Sterilization is carried out at the same time if the cat is not yet.
Pain management and care of the wound, which is extensive, are part of the treatment.
Close monitoring is implemented: regular palpation and chest x-rays at intervals defined by the veterinarian.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Early sterilization is the most effective preventive measure known for cats. Carried out before the first heatwave, it greatly reduces the risk of breast tumors; the benefit diminishes as the intervention is postponed and becomes weak after several years of cycles.
This is today the strongest medical argument in favor of early sterilization, beyond the sole question of unwanted litters.
Avoid hormonal treatments intended to block heat: surgical sterilization is safer and more permanent.
Palpating your cat's belly once a month, especially after six or seven years, allows you to spot a lump when it is still tiny.
Have the udders examined at each annual visit.
Possible complications
Extension to the lungs and lymph nodes, often early and sometimes already present at the time of diagnosis.
Ulceration of the skin over the masses, with infection, bleeding and pain.
Swelling of a hind limb due to blockage of lymphatic circulation.
Local recurrence after surgery, especially if the removal was not large enough.
Damage to the pleura with accumulation of fluid around the lungs and difficulty breathing.
When to see a veterinarian
You feel a lump, even tiny, along the breasts of your cat: consult without delay, do not monitor for months.
A udder is swollen, hot or painful.
The skin over a lump breaks open, oozes, or bleeds.
A hind leg swells.
Your cat is breathing quickly or with difficulty: emergency.
She loses weight, becomes weaker or hides.
Prognosis
The prognosis depends mainly on the size of the tumor at the time of the operation: the smaller the mass removed, the better the outlook. This is why you should never wait.
Involvement of the lymph nodes or lungs at diagnosis clearly clouds the outcome.
Extensive surgery, supplemented if necessary by chemotherapy, offers the best chance of control.
Monitoring after the operation continues over time, recurrences and extension may occur later.
Frequently asked questions
Can a lump under my cat's belly be benign?
It's possible, but in cats the majority of these masses are malignant, unlike what we observe in female dogs. Any breast lump must therefore be considered serious until proven otherwise, and reported quickly.
Does sterilization really protect?
Yes, it is a well-established protective effect. Sterilization carried out before the first heatwave greatly reduces the risk. The later it is, the more this benefit diminishes, without disappearing completely.
Why remove the entire breast chain and not just the ball?
Because tumor cells travel along the mammary chain and lymphatic vessels. Removing just the visible mass often leaves cells in place and exposes you to rapid recurrence.
My cat is old: is the operation worth it?
Age is not a disease. It is the condition of the heart, kidneys and the extent of the disease that decides. A preoperative assessment makes it possible to respond on a case-by-case basis, and ablation also relieves ulcerated and painful masses.
References
AAFP — American Association of Feline Practitioners
Content reviewed by the TunisieVet editorial team · Updated 09 August 2026
AT A GLANCE
Need a veterinarian?
Find a practitioner near you on TunisieVet, with their specialities, hours and contact details.
Find a veterinarianAffected species
This information is provided for educational purposes only and is not a substitute for a veterinary consultation. If you have any concerns about your animal's health, consult a veterinarian.
To discover
Related diseases and linked Animalia content.
Rabies
Viral · Vaccine available
Hip dysplasia
Other
Otitis externa
Environmental
Periodontal disease
Other