Lumps and bumps

Finding a lump on your pet can be a worrying experience. Although most lumps are harmless it is impossible to tell what a lump is simply by looking at it. If your pet has a swelling that lasts for more than a few days always ask your vet to check it for you.

There are many different things that can cause swellings: bruising or fluid build-up, abscesses, things attached to the skin, e.g. ticks (small parasites which latch onto your pet and suck blood swelling as they do so), and of course cancers. If you find any unusual lump or swelling on your pet you should make an appointment for your vet to check it out. Although most lumps are harmless, some can be very dangerous if left untreated. The biggest concern for most people is whether their pet has cancer.

Cancers are divided into two groups:

  • Benign: These lumps may grow bigger but do not spread elsewhere.
  • Malignant: More aggressive lumps, which not only grow but also spread through the body and may affect organs such as lungs and liver.

Some benign growths can also cause problems if they continue to grow. Even fatty lumps can grow to a huge size and may cause problems due to their size, e.g. restricting leg movement or pressing on the airways and causing breathing problems. Malignant growths are obviously more worrying – they must be removed before they have spread elsewhere.

Even your vet probably won’t be able to tell whether the lump is cancer, or some other kind of swelling, just by looking at it. There are several things to look for which may help your vet decide whether a lump on your pet is likely to be benign or malignant:

  • If the lump can be picked up in the fingers and moved around it is less likely to be aggressive. Malignant lumps often grow into the tissues beneath the skin and this makes them more difficult to remove.
  • If the lump grows very quickly it can soon cause problems even if it does not spread. Removing a large lump is much more difficult and leaves a bigger wound so fast-growing lumps should be removed while they are still small.
  • Malignant lumps often cause a reaction in the tissue around them – if any lump is red, painful when touched or is ulcerated or discharging then it should probably be removed.
  • Some cancers produce substances that make animals unwell – if your pet has a lump and shows signs of illness e.g. sickness, depression or excessive drinking then mention this to your vet when he examines your pet.

If a lump has been present for a long time without causing any problems it is unlikely to suddenly turn nasty. However, all lumps should be monitored closely. Feel the lump once a month (if you feel it too often you will not notice if it is growing slowly), and keep a note of its size. Ask your vet to measure the lump each year at the time of vaccination and record if it is growing. If the lump changes in any way, i.e. starts to grow more quickly, is sore or discharging, make an appointment for your vet to check the lump again.

If you find a lump on your pet your vet will want to examine the lump to see if they think it is likely to cause a problem. They will also examine your pet to see if they are otherwise healthy or if there are any other growths elsewhere. Unfortunately it will not be possible to say for certain that a growth will never cause problems just by looking at it.

If your vet is concerned they will take some samples from the lump to try to find out what sort of lump it is. Sampling a lump can be as easy as putting a needle into it to collect a few cells or it may be necessary to take a piece of the lump under anaesthetic. These samples can be sent to a pathologist at a laboratory who will be able to tell your vet what kind of lump it is. Once your vet knows this they will be able to advise you on the best treatment for your pet.

In most cases, the only treatment needed for small growths is to remove them. However, if it is a type of cancer that could spread elsewhere your vet may want to make sure that there is no sign of spread and to do this they may need to take X-rays or perform an ultrasound examination. If your pet is old or unwell your vet may want to take a blood sample to check your pet is healthy enough to have an anaesthetic.

In human medicine, skin lumps are often removed by a doctor using a local anaesthetic. It is unusual for this to be done in veterinary medicine. It is very important that the whole of a cancer is removed to make sure that it does not regrow. Even if the lump appears very small it may be necessary to cut quite deeply to remove all of it.

It is important that your pet lies still during the procedure – if they jump or move the operation will be more difficult and dangerous. It is necessary to give patients a sedative to make sure they stay still and sedation is no safer than a well-monitored anaesthetic. Sedated patients may take many hours to recover whereas the effects of a short anaesthetic should wear off more quickly in most animals. If you are worried about treatment of your pet, mention your concerns to your vet who will be happy to discuss all the options with you.

Fatty lumps

Probably the most common lump found on dogs is a fatty lump (lipoma). These are more common in obese animals. These are benign cancers that rarely spread and are often quite slow growing. However, over many years they can become very large and may need to be removed because they cause physical problems.

Sebaceous cysts

Often seen in older animals – these are swellings filled with a creamy substance similar to toothpaste. They are often found in the middle of the back. Sometimes the swellings become red and sore but normally they do not cause any problems. Sebaceous cysts can be removed but removing one does not stop others from developing.

Mast cell tumours (cancer)

These are one of the most common types of lumps found in the skin. Mast cells tumours are a type of cancer that can take on many different appearances and can easily be confused with all sorts of other lumps. Some mast cell tumours are harmless and cause no problems, others are very nasty cancers. It is difficult to tell how a mast cell tumour will behave and they can turn from a benign cancer to a malignant one so all mast cell tumours should be removed.


These are button like lumps about 1 cm across found on the skin of young animals. The lump may look quite red and usually comes up very quickly. Often they will go away as rapidly as they appeared without any treatment.


Warts look like small tags of skin. They are more common in older animals. Often animals that have a wart will go on to develop many others. Sometimes warts bleed and may be irritating in which case they will need to be removed.

Mammary tumours (breast cancer)

Lumps in the mammary glands of female dogs are very common and account for nearly half of all cancers in bitches. Most of these are relatively harmless but some of the most aggressive types of cancer can also be found here. Mammary lumps in male animals are often very nasty. Surgical removal of all mammary lumps is advisable and in some cases removal of all mammary tissue (mastectomy) is also necessary. Before removing mammary lumps your vet will want to check your pet thoroughly to make sure that the cancer has not spread anywhere else.

The most important thing to remember is that most lumps, even cancers, can be cured if they are caught early enough – so always check with your vet if you find anything unusual on your pet. In most cases your vet will be able to reassure you.