Skin Cancer in Dogs

Common Types of Skin Cancer in Dogs

Mast cell tumors

The most common skin cancer in dogs, usually in dogs around 8 to 10 years old. They can look like almost anything, including a soft lump that feels like a fatty lipoma, and they can swell and shrink from day to day.^6,5,14 Boxers, Boston Terriers, Staffordshire Bull Terriers and Labradors are among the breeds at higher risk.^5,14 See mast cell tumors in dogs.

Show photo: mast cell tumors on a dog's legs

Soft tissue sarcomas

Tumors of the connective tissue under the skin. They may feel soft or firm and can be mistaken for fatty lumps. They make up about 15% of skin and under-skin tumors.^15,16 They tend to grow back if not removed completely, so the first surgery is the best chance of a cure. Most low-grade sarcomas don't spread, but high-grade ones can.^17,16,15

Squamous cell carcinoma (SCC)

About 5% of canine skin tumors. Many are linked to sun exposure on pale, thinly haired skin, especially the belly and groin of white, short-coated breeds such as Dalmatians, Bull Terriers, pit bull types, Beagles and Whippets.^18,6,8 Sun damage often starts as red, crusty, thickened skin.^8,6 SCC can also grow under a toenail, mainly in older, large, dark-coated dogs such as Giant and Standard Schnauzers, Standard Poodles and Gordon Setters.^19,9 SCC is locally invasive but less likely to spread than many cancers.¹⁸

Melanoma

Pigmented growths on haired skin are usually benign (melanocytomas).^10,20 Melanomas in the mouth, on the lips or in a nail bed are much more likely to be malignant and to spread.^10,11,9 Breed matters too: most skin melanomas are benign in Dobermans and Miniature Schnauzers, while most are malignant in Miniature Poodles.²⁰

Other skin tumors

Basal cell tumors (many now called trichoblastomas) are common, usually benign, and often cured by surgery.^6,19 Skin lymphoma and other rarer cancers also occur, and a biopsy is needed to tell them apart.^12,1

Show photo: a skin tumor on a dog's head

How Vets Diagnose Skin Cancer

• Fine-needle aspirate: a quick needle sample, often done in the exam room without sedation. It identifies many tumors, including most mast cell tumors.^1,5,13
• Biopsy: a small piece of tissue, or the whole lump, sent to a pathologist. It's needed for a definite diagnosis and to grade the tumor.^1,5
• Staging: for cancers that may spread, your vet may check the nearby lymph nodes and do chest X-rays or an abdominal ultrasound.⁵

Knowing the type before surgery helps your vet plan how much tissue to remove. Sarcomas in particular shouldn't be "shelled out," because cells left behind make them grow back.¹⁷

Treatment

• Surgery is the main treatment for most skin cancers. Malignant tumors are removed with a margin of normal tissue around them, often 2 to 3 cm.^1,6,5
• Radiation therapy is often used when a tumor can't be fully removed.^5,17
• Chemotherapy and targeted drugs are used for cancers that have spread or are high grade.^5,12
• Other options for some tumors include electrochemotherapy (a chemotherapy drug combined with electric pulses) and, for oral melanoma, immunotherapy.^12,21,11

A veterinary oncologist can explain which options fit your dog's tumor type, grade and overall health.

Outlook

The outlook depends on the type, grade and stage of the cancer and whether it can be fully removed. Many low-grade mast cell tumors, low-grade sarcomas and sun-related SCCs caught early are cured with surgery.^14,16,18 Melanomas of the mouth and nail bed and high-grade tumors are more serious.^11,9,14 Finding lumps early, while they're small, gives the best chance of complete removal.⁷

Prevention and Early Detection

• Check your dog monthly. Run your hands over the whole body, including between the toes and inside the lips, and note any lumps.²²
• Follow the pea-and-a-month rule: have any lump 1 cm or larger that has been there for a month sampled, and don't let a lump grow past that size without having it checked.⁷
• Limit sun for pale, thin-coated dogs. Keep them indoors in the middle of the day on sunny days, use shade, and ask your vet about a dog-safe sunscreen or protective shirt. Don't use human sunscreen without checking first.^8,19

See also lumps and bumps on dogs, signs of cancer in dogs and cancer in dogs.

Frequently Asked Questions

What does skin cancer look like on a dog?

It can look like almost anything: a lump under the skin, a red or raw bump, a sore that won't heal, or a dark growth. That's why lumps need a needle sample.

What is the most common skin cancer in dogs?

Mast cell tumors.

Can dogs get skin cancer from the sun?

Yes. Squamous cell carcinoma is linked to sun exposure on pale, thinly haired skin.

How long can a dog live with skin cancer?

It varies widely by type and grade. Many dogs are cured by surgery, while aggressive types have a shorter outlook. Your vet can give a more specific answer after a biopsy.

Are cancerous lumps on dogs hard or soft?

Either. Some cancers feel soft and movable, like a fatty lump.