Finding a new lump, bump, sore, or unusual patch of skin on your dog can be worrying. While many skin growths in dogs are benign, some can be cancerous and require prompt veterinary attention.

Knowing the signs of skin cancer in dogs can help pet owners recognize suspicious changes early. Dog skin tumors can look very different depending on the type of tumor. Some appear as small lumps, while others may look like discolored patches, ulcers, crusts, or wounds that do not heal.

Importantly, you cannot determine whether a skin growth is cancer simply by looking at it. Benign and malignant growths can look similar, so a veterinarian may need to examine cells with a fine-needle aspiration or perform a biopsy.

This guide explains the most common dog skin cancer signs, what different suspicious growths may look like, when to contact a veterinarian, and how skin tumors are diagnosed and treated.

What Is Skin Cancer in Dogs?

Skin cancer occurs when abnormal cells grow uncontrollably in the skin or tissues underneath it.

Dogs can develop many different types of skin tumors. Some are benign, meaning they do not invade surrounding tissue or spread to distant organs. Others are malignant and may invade nearby tissues or metastasize to other parts of the body.

Skin tumors are among the tumors most commonly noticed by dog owners because they are visible and can often be felt beneath the skin.

The appearance of a tumor can vary considerably, which is why professional evaluation is important.

10 Important Dog Skin Cancer Signs

Not every unusual skin change means cancer. However, the following signs deserve veterinary attention, particularly when they are new, growing, changing, or persistent.

1. A Lump That Keeps Growing

One of the most important warning signs is a lump that continues to increase in size.

A suspicious mass may start small and gradually become larger. Some cancerous tumors can also grow quickly.

However, growth alone does not prove that a mass is cancerous. Some benign growths can also become larger over time.

If you discover a new lump on your dog, have it examined by your veterinarian rather than trying to identify it yourself.

2. A Lump That Changes Shape or Texture

A mass that suddenly becomes harder, softer, irregular, swollen, or otherwise different deserves attention.

Veterinary sources recommend monitoring lumps for changes in size and texture.

A tumor may feel:

• Firm
• Soft
• Nodular
• Raised
• Irregular
• Deep beneath the skin

Because different tumors can have very different appearances, physical examination and diagnostic testing may be necessary.

3. A Skin Growth That Bleeds or Ulcerates

Some skin tumors can develop ulcers or break open.

You may notice:

• Bleeding
• Crusting
• Oozing
• Discharge
• An open wound
• Repeated scabbing

A persistent sore that does not heal normally should be examined by a veterinarian.

Squamous cell carcinomas, for example, may appear as firm, raised, ulcerated patches or lumps.

4. A Wound That Does Not Heal

A small injury should generally improve as it heals.

If a sore repeatedly opens, becomes crusty, bleeds, or fails to heal, it should not simply be assumed to be an infection or minor irritation.

Persistent sores and swellings are among the general warning signs that warrant veterinary evaluation.

5. A New Dark or Pigmented Growth

Some tumors can appear dark because they contain pigment.

Melanocytic tumors can appear as spots, patches, plaques, or raised masses. Some are benign, while malignant melanomas can be aggressive.

Pay particular attention to new or changing dark growths around the:

• Lips
• Mouth
• Nail beds
• Toes
• Abdomen
• Scrotum

A dark growth does not automatically mean melanoma, but a veterinarian should evaluate suspicious changes.

6. Swelling Around a Toenail or Nail Bed

A persistent problem involving a toe or nail can sometimes be more than an infection or injury.

Possible warning signs include:

• Swollen toe
• Missing nail
• Nail deformity
• Bleeding
• Persistent licking
• Pain
• Limping
• Recurrent infection

Certain tumors, including squamous cell carcinoma and melanoma, can develop around the nail bed.

If an older dog develops a persistent or unexplained toe problem, veterinary examination is particularly important.

7. Persistent Red, Crusty, or Irritated Skin

Skin cancer can sometimes resemble an ordinary skin irritation.

A suspicious lesion may appear as:

• Red skin
• Thickened skin
• Crusts
• Plaques
• Irritated areas
• Raised patches
• Ulcers

Squamous cell carcinoma may initially resemble a small irritated or ulcerated area.

Because allergies, infections, parasites, and inflammatory diseases can produce similar signs, diagnosis should be left to a veterinarian.

8. A Lump That Suddenly Changes

A lump that has been stable for months or years may become concerning if it suddenly changes.

Watch for:

• Rapid growth
• Sudden shrinking
• Bleeding
• New redness
• Change in firmness
• Ulceration
• Increased sensitivity
• Hair loss over the lump

A sudden change does not prove cancer, but it is a good reason to schedule a veterinary examination.

9. Pain, Licking, or Scratching at a Growth

Some tumors may become irritated or painful.

Your dog may repeatedly:

• Lick the area
• Scratch it
• Bite it
• Rub against furniture
• Avoid being touched

For tumors affecting the toes or nail beds, pain may lead to limping or reluctance to walk.

10. General Signs of Illness

Advanced or more serious cancer can sometimes cause signs beyond the skin.

These may include:

• Unexplained weight loss
• Reduced appetite
• Low energy
• Swollen lymph nodes
• Persistent vomiting or diarrhea
• Lameness
• Unexplained bleeding
• Difficulty breathing

These symptoms have many possible causes and do not automatically indicate cancer. However, persistent or unexplained symptoms should be evaluated by a veterinarian.

Common Types of Skin Cancer in Dogs

Several different tumors can affect a dog’s skin.

Mast Cell Tumors

Mast cell tumors are among the most common malignant skin tumors in dogs.

They can appear as raised lumps and may range from soft to firm. They can occur on different parts of the body and may change in size.

Some mast cell tumors can release substances that cause additional problems, including gastrointestinal ulceration.

Melanoma

Melanomas develop from pigment-producing cells.

In dogs, malignant melanomas are especially important when they occur in areas such as the mouth, lips, or nail beds. They can appear dark, but some malignant melanomas may not be heavily pigmented.

Squamous Cell Carcinoma

Squamous cell carcinoma is a malignant tumor that can develop in the skin.

It may appear as a firm, raised, irregular, crusted, or ulcerated lesion. Some forms are associated with prolonged sun exposure, particularly in lightly pigmented or sparsely haired areas.

Basal Cell Tumors and Carcinomas

Basal cell tumors are relatively common in dogs and are often benign.

They can appear as firm, dome-shaped, elevated masses and may be hairless or ulcerated.

Because benign and malignant growths can look similar, veterinary evaluation is still important.

Which Dogs Are More at Risk?

Skin tumors can occur in dogs of many ages and breeds.

Some tumors are more common in older dogs, while certain breeds may have increased risk for particular tumor types.

For example, mast cell tumors are seen commonly in older dogs and are more frequently recognized in breeds including Boxers, Pugs, Rhodesian Ridgebacks, and Boston Terriers.

Age, genetics, pigmentation, sun exposure, and other factors can influence risk depending on the tumor type.

How Is Dog Skin Cancer Diagnosed?

A veterinarian cannot reliably determine whether a growth is cancerous just by looking at it.

Diagnostic options may include:

Physical Examination

The veterinarian will assess the size, location, appearance, and texture of the growth.

Fine-Needle Aspiration

A small needle may be used to collect cells from a mass for microscopic examination.

Biopsy

A tissue sample may be removed and examined by a veterinary pathologist.

Imaging

X-rays, ultrasound, CT, or other imaging may be recommended when there is concern about deeper invasion or spread.

Accurate diagnosis is important because treatment depends on the tumor type, location, size, grade, and whether it has spread.

Treatment for Skin Cancer in Dogs

Treatment depends on the type and stage of the tumor.

Possible treatments include:

• Surgical removal
• Radiation therapy
• Chemotherapy
• Immunotherapy or targeted treatments in selected cases
• Combination treatments

Surgery is commonly used for localized skin tumors when complete removal is possible.

Some tumors require removal of surrounding healthy tissue to reduce the risk of leaving cancer cells behind.

A veterinary oncologist may be involved when tumors are aggressive, difficult to remove, or have spread.

Can Dog Skin Cancer Be Prevented?

Not every skin tumor can be prevented.

However, reducing excessive sun exposure may help reduce the risk of certain sun-associated skin cancers.

Additional preventive steps include:

Check Your Dog’s Skin Regularly

Run your hands gently over your dog’s body and look for new lumps, bumps, sores, or discoloration.

Record Changes

If you find a lump, note its location and monitor its size. Taking periodic photographs can help document changes.

Avoid Excessive Sun Exposure

Dogs with lightly pigmented or sparsely haired skin may need additional protection from excessive sunlight.

Schedule Routine Veterinary Exams

Regular examinations can help identify suspicious growths before they become advanced.

When Should You Take Your Dog to the Vet?

Make a veterinary appointment if you notice:

• A new lump
• A lump that is growing
• A changing mass
• A persistent sore
• Repeated bleeding
• A dark or unusual growth
• A swollen toe
• Nail loss
• A lesion that does not heal
• A painful skin growth
• Unexplained weight loss or weakness

Do not wait for a lump to become large before having it checked.

Early evaluation can make diagnosis and treatment easier in many cases.

Frequently Asked Questions

What does skin cancer look like on a dog?

There is no single appearance. Skin cancer may look like a growing lump, raised or discolored patch, ulcer, crust, wart-like growth, or persistent sore. Some tumors are dark, while others are not.

Are all lumps on dogs cancerous?

No. Dogs commonly develop benign growths such as lipomas and other noncancerous tumors. However, appearance alone cannot reliably distinguish benign from malignant masses.

Is a black lump on my dog always cancer?

No. Some benign growths can be pigmented. However, a new, changing, raised, bleeding, or ulcerated dark growth should be evaluated by a veterinarian.

Can skin cancer in dogs be cured?

Some localized skin tumors can be successfully treated, particularly when completely removed early. Prognosis depends heavily on the specific tumor type, grade, location, and whether it has spread.

How quickly does dog skin cancer grow?

Growth rates vary dramatically. Some tumors grow slowly, while others can enlarge quickly. A rapidly changing lump should be examined promptly.

Can dogs get skin cancer from the sun?

Certain canine skin cancers, including some squamous cell carcinomas, can be associated with prolonged sun exposure. Sun protection can therefore be useful, especially for dogs with lightly pigmented or sparsely haired skin.

Final Thoughts

Knowing the signs of skin cancer in dogs can help you recognize potentially serious changes early. A growing lump, persistent sore, bleeding lesion, unusual dark growth, swollen toe, nail loss, or rapidly changing skin mass should not be ignored.

At the same time, remember that not every lump or skin problem is cancer. Dogs can develop many benign growths and common skin conditions that look similar to tumors.

The only reliable way to determine what a suspicious growth is involves veterinary assessment and, when necessary, diagnostic testing such as fine-needle aspiration or biopsy.

Regularly checking your dog’s skin, scheduling routine veterinary examinations, and seeking professional advice when you notice a new or changing growth are some of the best ways to protect your dog’s health.

If a suspicious lesion is found, don’t attempt to remove it or treat it with home remedies. Early veterinary evaluation gives your dog the best opportunity for an accurate diagnosis and appropriate treatment.