Dog Has a Lump: What It Could Be and When to See the Vet

Discovering a new lump on your dog is alarming. Here's the reassurance and the reality: most lumps on dogs are benign, but a meaningful proportion are not, and the appearance alone cannot reliably tell you which is which. Early diagnosis consistently improves outcomes.

Common Benign Lumps

Lipoma

The most common lump in dogs — a benign collection of fat under the skin. Soft, freely movable, well-defined, slow-growing. Common in middle-aged to older dogs and certain breeds (Labrador, Beagle, Spaniel). Usually no treatment needed unless it interferes with movement.

Sebaceous Cyst

A blocked sebaceous gland. Small, firm, sometimes with white-yellow contents. Can become inflamed if infected. Benign but may occasionally need veterinary drainage.

Histiocytoma

A pink, smooth, domed lump that appears suddenly, especially in dogs under 3 years old. Resolves spontaneously in 1–3 months in most cases. Very benign.

Viral Papillomas (Warts)

Caused by canine papillomavirus. Common in the mouth and on the lips of puppies or immunosuppressed dogs. Disappear on their own within weeks to months.

Abscess

A localised collection of pus after a bite wound, scratch, or foreign body. Warm, painful, fluctuant. Requires veterinary drainage and antibiotics.

Malignant Conditions to Rule Out

Mast Cell Tumour (MCT)

The most common malignant skin tumour in dogs. It can look exactly like a harmless lipoma — soft, pink, slow-growing. External appearance alone cannot distinguish it. Cytological diagnosis is essential.

Melanoma

Most common in the oral cavity and pigmented areas. Malignant with a high tendency to metastasise.

Fibrosarcoma

A connective tissue tumour, often firm and fixed to deeper structures.

Osteosarcoma

Bone tumour, primarily affecting the limbs of large breeds. Presents as progressive swelling and pain.

Assessing a Lump at Home

Before the vet visit, note down:

• Exact location (skin surface, subcutaneous, deeper)
• When did it appear? Is it growing?
• Soft or firm? Mobile or fixed?
• Is the overlying skin normal, red, or ulcerated?
• Is the dog sensitive when you touch the area?
• Any other symptoms — weight loss, reduced energy, appetite changes?

Photograph the lump and measure it. Store dated photos in Purzi for tracking changes over time.

When to Go to the Vet Urgently

• Rapid growth over days
• Ulcerated, bleeding, or discharging
• Severe pain when touched
• Accompanied by breathing difficulty or trouble swallowing

What the Vet Will Do

The key diagnostic tool is a fine needle aspirate (FNA): a thin needle inserted into the lump to collect cells for microscopic examination. It's quick, inexpensive, and highly informative — the first step for any new skin mass.