Mammary Tumours in Cats

Mammary tumours are among the most frequently diagnosed cancers in older, unspayed female cats. These tumours can significantly impact a cat’s health and wellbeing, particularly if they are malignant and left untreated. Early identification and prompt veterinary intervention are essential to improving outcomes and ensuring the best possible quality of life. Despite their seriousness, mammary tumours can be effectively managed in many cases when addressed early and treated appropriately.

This article provides a comprehensive overview of mammary tumours in cats, including the causes, risk factors, clinical signs, diagnostic process, and treatment options available. Read on to find out everything you need to know about this condition.

What Is a Mammary Tumour?

A mammary tumour is a lump that forms due to abnormal cell growth in a cat’s mammary glands. These glands, which are responsible for producing milk, run in two rows along your cat’s underside; there are usually four pairs. They start near the chest and end close to the back legs. Tumours can develop in any of these glands and may feel like small, firm lumps just under the skin. Sometimes, there might be more than one lump, and in some cases, they can become sore, inflamed, or even ulcerated.

Mammary tumours can be either benign (non-cancerous) or malignant (cancerous). Benign lumps tend to grow slowly and don’t usually spread to other parts of the body. However, in cats, most mammary tumours are unfortunately malignant. In fact, studies show that around 85% to 96% of mammary lumps in cats turn out to be cancerous. The most common type is called an adenocarcinoma, which starts in the glandular tissue that produces and transports milk.

Malignant tumours are more serious because they don’t just grow in one place—they can invade nearby tissue and spread to other parts of the body. This spreading process is called metastasis. These tumours often reach the nearby lymph nodes first and can then spread further, commonly affecting the lungs and other internal organs if not caught early. Because of this, early detection and treatment are incredibly important when it comes to improving your cat’s chances of a good outcome and maintaining their quality of life.

Which cats are at risk?

There are several known risk factors that can increase the chances of a cat developing mammary tumours. Some of these are related to the cat’s sex, age, breed, and hormone exposure throughout their life.

Spaying and hormone levels play a major role

Female cats that haven’t been spayed (also known as “intact” females) are at a much higher risk of developing mammary tumours than those that have been neutered. The hormones oestrogen and progesterone, which are produced during a female cat’s reproductive cycles, are believed to encourage the growth of certain types of mammary cells, increasing the chance of abnormal cell changes over time. Thankfully, spaying can dramatically reduce this risk. If a female cat is spayed before 6 months of age, her risk of developing mammary cancer later in life can be reduced by around 91%. Even spaying before the age of one can still reduce the risk by approximately 86%.

Age is another factor

Mammary tumours are most often diagnosed in middle-aged to older cats, typically between 10 and 12 years old. However, they can occasionally occur in younger or older cats as well.

Breed can also play a role

Certain breeds, such as Siamese and Persian cats, appear to be more prone to developing mammary tumours. Siamese cats, in particular, are reported to be at a higher risk and may develop more aggressive forms of the disease at a younger age than other breeds.

Male cats are rarely affected by mammary tumours, but it’s not impossible

This is primarily because they have very low levels of the hormones involved in mammary development. However, on the rare occasions when a male cat does develop a mammary tumour, it tends to be malignant and quite aggressive, so early detection and treatment are especially important.

Understanding these risk factors can help cat owners make informed decisions about neutering and be more aware of the signs to watch for as their cats age.

Clinical signs of mammary tumours in cats

In the early stages, mammary tumours in cats often develop without causing any obvious signs of illness. This can make them easy to miss at first. However, as the tumour grows or spreads, certain symptoms may start to appear, and being able to spot them early can make a big difference.

One of the most common signs is a firm lump or nodule near one of the nipples

These lumps can vary in size, from something as small as a pea to a much larger mass. They’re usually found just under the skin, along your cat’s underside, and may be singular or appear as multiple growths.

As the tumour gets bigger, it may become ulcerated, meaning the skin over it breaks open. This can lead to bleeding, scabbing, or discharge, which are definite red flags that veterinary attention is needed. The area may also feel sore or tender, and some cats will groom the site excessively or show signs of discomfort when touched.

If the cancer has begun to spread, you might also notice swollen lymph nodes, particularly in the armpit area (known as the axilla) or near the groin (inguinal region). These swellings may feel like additional lumps and can be a sign that the tumour has started to move beyond the original site.

In more advanced cases – especially when the cancer has metastasised (spread to other parts of the body, such as the lungs) – cats may show general signs of being unwell, such as lethargy, a decreased appetite, or even weight loss. These symptoms can be caused by the tumour itself or by the body’s response to the cancer spreading internally.

The importance of regular checks

Regularly checking your cat at home for any new or unusual lumps, especially in the belly and chest areas, is a simple yet important way to catch problems early. If you spot anything unusual, it’s always best to get your cat checked by a vet as soon as possible.

Diagnosis of mammary tumours in cats

The diagnosis of mammary tumours in cats involves several important steps to confirm the type of tumour present, its stage of advancement, and whether it has metastasised to other parts of the body. Obtaining a clear and accurate diagnosis is crucial in determining the most suitable treatment and providing the best possible prognosis.

The first stage usually starts with a thorough physical examination. Your vet will examine your cat’s mammary glands and surrounding tissues, including gently palpating for any enlarged lymph nodes, particularly those in the armpits (axillary nodes) and groin area (inguinal nodes). Swollen nodes in these regions can be a sign that the tumour may be spreading.

Why biopsies are useful

To investigate further, your vet may carry out a procedure called a fine-needle aspiration (FNA). This involves using a thin needle to collect a small sample of cells from the lump, which is then examined under a microscope. While this can provide useful clues about the nature of the growth, it often isn’t enough to fully confirm whether the tumour is cancerous or how aggressive it is. For a definitive diagnosis, a biopsy, where a larger tissue sample is taken, is needed. This sample is sent to a specialist laboratory for histopathology, a detailed analysis that helps determine the exact type of tumour and its grade (how aggressive the cancer cells look).

Once a diagnosis is confirmed, the next step is staging – this means assessing how far the cancer has spread in the body. Staging is vital for deciding on treatment options and predicting likely outcomes.

Staging often includes:

Blood tests to check your cat’s overall health and detect any underlying issues with organs like the liver or kidneys. This typically includes haematology (a blood cell count), biochemistry, and urinalysis.

Diagnostic imaging to look for signs of spread. Most commonly, this involves chest x-rays or a CT scan to check for tumours in the lungs — a common site of metastasis. An abdominal ultrasound may also be used to examine internal organs, and further FNA samples from the lymph nodes may be taken to check for cancer cells there.

Vets often use a system called the TNM staging system

This was originally developed by the World Health Organization, to describe the extent of the cancer. TNM stands for:

T – Tumour size

N – Node involvement (whether nearby lymph nodes are affected)

M – Metastasis (whether the cancer has spread to distant organs)

Early diagnosis and staging not only help guide treatment choices but also allow for more accurate discussions about prognosis, costs, and the potential benefits and risks of surgery, chemotherapy, or palliative care.

Treatment Options

1. Surgery

Surgery is usually the most effective treatment for mammary tumours in cats. A local mastectomy can be performed when one gland is removed, or a regional mastectomy, where more than one gland in an area is removed. Often, the best surgical option is something called a mammary strip, which involves removing the entire chain of mammary glands (not just the lump itself). While this may sound drastic, it greatly reduces the risk of the tumour coming back and can improve long-term survival.

If your cat has lumps on both sides of the body, your vet might suggest doing a bilateral mastectomy, where both sets of mammary glands are removed. This is usually done in two separate surgeries to allow recovery between procedures.

2. Chemotherapy

Because many feline mammary tumours are aggressive and can spread to other parts of the body, chemotherapy is often recommended, especially if the tumour has already started to spread or if the tumour is considered high-grade.

A common chemotherapy drug used is doxorubicin, and it’s often combined with another medication called cyclophosphamide. While chemotherapy doesn’t work for every cat, lots do show some improvement, and some can go into temporary remission, meaning the tumour shrinks or disappears for a while.

There are also newer chemotherapy options available. For example, tyrosine kinase inhibitors (like toceranib) and low-dose continuous chemotherapy (called metronomic chemo) are sometimes used for cats that aren’t suitable for more intense treatments or where the main goal is to slow the cancer down and maintain comfort, rather than cure it.

3. Supportive and Palliative Care

Not every cat will be a good candidate for surgery or chemotherapy. For example, if your cat is very elderly, has other serious health problems, or if the cancer has spread too far, your vet may recommend palliative care, which means managing the symptoms and keeping your cat comfortable, rather than trying to cure the disease.

Options for palliative care may include:

Removing the tumour partially to reduce pain or discomfort, especially if it’s ulcerated (open and sore).

Pain relief and anti-inflammatory medication to help keep your cat comfortable.

Wound care and antibiotics, if the tumour has become infected.

Nutritional support ensuring your cat maintains a healthy appetite and energy levels.

Emotional and environmental support, including keeping stress levels low and maintaining a calm, familiar home environment.

Even if curative treatment isn’t possible, there’s still a lot that can be done to improve your cat’s quality of life and make sure their final months or years are as happy and pain-free as possible

Prognosis and Survival

The outlook for cats with mammary tumours depends on a few key factors — mainly tumour size, whether the cancer has spread, and how aggressive the tumour appears under the microscope.

1. Tumour Size

Tumour size is a strong predictor of outcome:

Less than 2 cm – Best prognosis; cats can live over three years post-surgery.

2 to 3 cm – Moderate outlook; survival is typically around two years.

Over 3 cm – More serious; average survival drops to around six months.

2. Metastatic Disease

If the tumour has spread to lymph nodes, lungs, or other organs, the prognosis worsens. This is why staging tests like scans and bloodwork are so important to understand the extent of the disease before starting treatment.

3. Tumour Grade

Tumours are graded based on how abnormal the cells look:

Low-grade tumours grow more slowly and are less likely to spread.

High-grade tumours are more aggressive and linked to a poorer prognosis.

Can mammary tumours be prevented?

While we can’t always prevent mammary tumours entirely, there are some very effective ways to reduce the risk, particularly when action is taken early in life.

1. Early Neutering

The most effective preventative measure is spaying female cats before their first season. Doing so can reduce the risk of developing mammary tumours by over 90%. Spaying before six months of age offers the greatest protection, while spaying before 12 months still significantly lowers the risk.

This is because hormones like oestrogen and progesterone are thought to fuel abnormal growth in mammary tissue. The longer a cat remains unspayed, the more exposure she has to these hormones, increasing her risk over time.

2. Avoid Hormonal Medications

Medications used to suppress seasons (such as synthetic progestins) can increase the risk of mammary changes and are best avoided unless absolutely necessary and under veterinary advice.

3. Monitoring at home

Get into the habit of gently feeling along your cat’s underside when grooming or stroking them. Look out for any small lumps, bumps, or swellings around the nipples. Early detection can make a big difference to outcomes.

4. Regular Vet Visits

Routine health checks are key, especially for middle-aged or older cats, or those from at-risk breeds such as Siamese or Persian cats. Your vet may spot changes long before they become obvious at home.

Conclusion

Effective management of mammary tumours in cats relies on a timely and well-rounded approach. The most important steps include early recognition of changes, accurate diagnosis, surgical removal, and, where appropriate, follow-up treatment such as chemotherapy or supportive care. When these tumours are detected at an early stage, particularly while still small, outcomes can be significantly more favourable. A proactive response greatly improves the chances of long-term control. If you notice any lumps, swelling, or unusual changes around your cat’s mammary area, it’s essential to seek veterinary advice without delay. Early intervention can be life-saving.