Updated October 13, 2026. Fact-checked against veterinary sources; review by a licensed veterinarian is in progress. See our editorial policy.
Quick answer: Cancer is much less common in young dogs than in older ones, and many lumps in puppies and young adults are harmless, such as histiocytomas and warts. But some serious cancers, including lymphoma, mast cell tumors, and bone cancer in giant breeds, can occur in dogs under 5. Any new lump, lasting lameness, or unexplained weight loss in a young dog should be checked.
Common benign growths in young dogs
- Histiocytomas: small, round, often red, hairless lumps, common in dogs under 3. Most go away on their own within a few months.
- Viral papillomas (warts): cauliflower-like growths, often in the mouth. See dog warts.
Cancers that can affect young dogs
- Lymphoma: swollen lymph nodes
- Mast cell tumors: including in young Boxers, Pugs, and Shar-Peis
- Osteosarcoma: can occur in young giant-breed dogs, causing lameness and swelling
- Soft tissue sarcomas and other tumors, less commonly
Warning signs
- A lump that grows, changes, or lasts more than a month
- Lameness that doesn’t improve
- Swollen lymph nodes
- Weight loss or poor appetite
What to do
A quick needle sample usually tells whether a lump is harmless. See fine needle aspirates.
Sources
- Merck Veterinary Manual: Histiocytomas in dogs
- Merck Veterinary Manual: Neoplasia in dogs
- Veterinary Cancer Society: Warning signs of cancer in pets
This article is for general education and is not a substitute for care from your own veterinarian. Learn about The Pet Vet and our editorial policy.