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Lumps, Bumps and Skin Tumours in Dogs

How often have you been patting your dog and discovered a lump? Skin cancers are by far the most common cancers in dogs, with around 20 to 30% found to be malignant. Cats have a much lower incidence of skin cancer, but a higher percentage – over 50% – are malignant.

While this means more than half the lumps we might detect on our dogs are benign, just like us, it’s very important to investigate promptly every unusual lump or skin mark you discover on your pet.

Typically, benign tumours grow slowly (if at all) and they are well circumscribed, non-painful and can remain unchanged for years. Malignant tumors are more likely to grow rapidly, have poorly defined margins, infiltrate into the surrounding tissues, and may be ulcerated.

While the list below does not cover all the skin tumours diagnosed in dogs, these are some of the most common lumps and bumps.

Sebaceous cysts

These cysts are the result of blocked oil glands. They rarely grow to more than 1cm across and can occur anywhere over the body. They do appear to be more common in older dogs and while it’s sensible to get veterinary advice to confirm the diagnosis, no treatment is required for sebaceous cysts.


Soft fatty tumours are most often seen (or felt) in middle-aged or older dogs. Large overweight dogs of any breed are more prone to lipomas, and while they can develop anywhere over the body, they occur mostly around the ribs and often as multiple lumps.

While fatty tumours are benign (so won’t spread to other organs), it’s still important to find out if your dog’s lump is in fact a benign fatty tumour.

Diagnosis is easy – at CVH we take a fine needle aspirate from the lump and look at the tumour cells under the microscope. Fat cells are straightforward to diagnose.

Lipomas can grow to quite a large size and in some cases, will start to impact on a pet’s mobility. In these cases we recommend surgery to remove the tumour, otherwise all that’s usually required by the pet owner is regular monitoring of the tumour’s size and appearance once diagnosis is confirmed.

The dog pictured on the right is prepped for surgery to remove a massive lipoma. While the surgery was successful, it would have been much better for the dog and our vets if the owners had sought veterinary advice much earlier. Carrying around a lipoma this size is uncomfortable for any pet and, the larger the tumour, the more complex and extensive a blood supply is required to support the mass making surgery more challlenging.



Mast cell tumours

Mast cell tumours are the most common malignant skin cancer in dogs. They can occur in any breed but are most frequently diagnosed in boxers, Boston terriers, labradors, pugs, Staffordshire terriers and schnauzers. In healthy dogs, mast cells occur throughout the body and help animals respond to inflammation and allergies. When they become cancerous, they can develop rapidly into serious, life-threatening disease.

Mast cell tumours are a good example of why it’s so important to have any lump or skin lesion examined promptly. They are very variable and can appear small and insignificant, but when first noticed they are usually raised and around 1 cm in diameter. They are found most commonly on the trunk, limbs, and perineal (genital) area. Early surgery to remove the lesion and prevent spread of the cells to other parts of the body is essential. Follow-up pathology to confirm the diagnosis is important to guide future treatment. If caught early enough, surgery will stop further spread.


In dogs, melanomas are not related to sun exposure and they are not always malignant. The most dangerous occur in dark pigmented areas of the skin including inside the mouth, on the paws, or in the eyelid tissues. These pigmented areas may be normal for that pet – for example, a black Labrador – but any darkly pigmented, raised, thickened or ulcerated growth on your dog needs to be checked promptly. Diagnosis by fine needle aspirate helps determine the course of treatment – that could mean surgery if the lump is easily removed.

Squamous cell carcinomas

Another quite common skin cancer in dogs, squamous cell carcinomas (SCC) are usually the result of too much sun exposure and frequently occur in white-skinned dogs. White dogs with thin coats or hairless areas – such as bull terriers and dalmations – can develop a SCC on their tummy for example, if they are allowed to lie in the sun, belly up, for long periods.

Squamous cell carcinomas are one of the most common and dangerous skin cancers in cats – especially cats with white ears and non-pigmented noses. The usual sites for this cancer are the front of the nose, eyelids, lips and ear tips. It’s essential – as with white-skinned dogs – that these pets are kept inside or, at the very least, allowed only minimal time in the sun. SCCs in cats become invasive quickly. Early treatment can include surgery and/or cryosurgery, more advanced cases require radiation therapy and have a poor prognosis.

Diagnosis and Treatment

Regardless of the size, shape or appearance of a new skin lesion or lump on your pet, please make sure you have a prompt check up. It’s often an easy exercise to determine if the lump needs immediate treatment or if it just needs monitoring over time.

The specific treatment for any lump and bump found in or on your dog or cat’s skin will depend on the tumor's type, location, size, and whether the cancer has spread to other organs. If required, surgical removal of the tumor remains the treatment of choice, but other forms of therapy such as radiation and chemotherapy are available.