Understanding the Most Common Types of Skin Cancer in Dogs
Skin cancer tops the list of tumors diagnosed in dogs. While many skin tumors are benign, some can be aggressive and life-threatening if not treated quickly. Genetics, age, sun exposure, environmental chemicals, hormonal imbalances, and certain viral infections all play a role in their development. Not every lump or bump on your dog's skin is cancerous, but new or changing growths should always get a veterinarian's attention. Let's dive into the most common types of skin cancer seen in dogs and what you should watch for.
Mast Cell Tumors (MCTs)
Mast cell tumors are the most common malignant skin tumors in dogs, making up about 20% of all canine skin tumors. These arise from immune cells called mast cells, which release chemicals like histamine during allergic reactions. MCTs can look like almost anything — warts, skin tags, or raised, red, ulcerated lumps. They might change size and can cause swelling or even systemic symptoms such as itching, stomach ulcers, or lethargy. Boxers, Boston Terriers, Bulldogs, Pugs, Rhodesian Ridgebacks, Golden Retrievers, Labrador Retrievers, and older mixed breeds are especially at risk. Diagnosis usually involves a fine needle aspiration or biopsy. Surgical removal is the first line of treatment, and low-grade tumors often mean a full recovery. High-grade tumors may come back or spread and could require chemotherapy or radiation therapy.
Malignant Melanoma
Malignant melanoma starts in pigment-producing cells called melanocytes. Most often, it shows up as a solitary, raised, dark lump — especially around the mouth, nail beds, lips, or sometimes on haired skin. While many cutaneous melanomas are benign, malignant forms can spread rapidly to vital organs. Miniature and Standard Schnauzers, Scottish Terriers, and black-coated dogs (especially males) face higher risk. Oral and digit melanomas can cause swelling, nail loss, or even bone destruction. The main treatment is surgical removal; in metastatic cases, follow-up therapy or even an immunotherapy vaccine may be used.
Squamous Cell Carcinoma (SCC)
Squamous cell carcinoma is a malignant tumor from the skin's squamous cells. Older dogs and breeds like Dalmatians, Bull Terriers, Whippets, Basset Hounds, Beagles, Collies, Keeshonds, and white-coated dogs are more prone. SCCs often look like firm, raised, wart-like or ulcerated lumps on the head, lower legs, abdomen, or back. Sun exposure is a big risk factor; papillomavirus infection may also play a part. Under-the-nail SCC is more common in dark-coated breeds and can cause toe swelling or lameness. Most SCCs are isolated but can become invasive. Surgery is typical for treatment; sometimes radiation or photodynamic therapy is added. Early detection really matters here.
Histiocytic Cell Tumors
Histiocytic tumors come from skin histiocytes and are most common in young dogs under three years old. Breeds like Scottish Terriers, Bulldogs, Greyhounds, Boxers, Boston Terriers, and Shar Peis are more likely to get them. Histiocytomas usually appear as small, raised, pink, hairless lumps on limbs or the head and often go away on their own within weeks. Systemic and malignant forms mostly affect Bernese Mountain Dogs and can involve multiple skin or internal lesions. Diagnosis is by biopsy. Most histiocytomas resolve naturally; systemic or malignant types may need chemotherapy.
Fibrosarcoma
Fibrosarcomas are tumors of connective tissue just under the skin. They tend to affect middle-aged and older dogs and show up as firm, slow-growing lumps on the trunk, limbs, mouth, or nose. Though they rarely spread to distant organs, they're locally invasive and often come back after surgery. Multiple tumors in one area can happen. Surgery is the main treatment; radiation and chemotherapy may be needed if tumors are aggressive or keep recurring.
Other Skin Tumor Types
- Lipomas: Benign fatty tumors found in older or obese female dogs (especially Dobermans, Labs, Miniature Schnauzers). Usually harmless unless growing fast.
- Sebaceous adenomas: Benign oil gland tumors common in older small breeds (Poodles, Shih Tzus). Typically small and hairless.
- Papillomas: Wart-like viral growths in younger or immune-compromised dogs; often resolve on their own.
- Hair follicle tumors: Mostly benign cystic nodules; rarely malignant but may need removal.
- Blood vessel tumors: Hemangiomas are benign; hemangiosarcomas are malignant and linked to sun exposure in light-skinned breeds.
- Basal cell tumors: Dome-shaped lumps on head/neck/forelimbs; most are benign but some carcinomas can spread locally.
Diagnosis and Treatment
If you spot a new or changing lump on your dog, your vet will likely use fine needle aspiration or biopsy to identify the tumor type. Sometimes advanced imaging (like X-rays or MRI) helps check for internal spread. For most skin tumors caught early, surgical removal is effective. Aggressive or metastatic tumors might require chemotherapy, radiation therapy, or immunotherapy. Benign tumors are sometimes left alone unless they bother your dog.
Prevention and Monitoring
Check your dog's skin regularly for new lumps or sores that don't heal. Dogs with light skin and thin fur—especially those who spend time in the sun—are more at risk. Limiting sun exposure during peak hours can help reduce risk. Early diagnosis means a better chance for a healthy life after treatment. If you find any unexplained lump or discoloration on your dog's skin, see your veterinarian promptly.
