TL;DR: A rapidly growing lump requires veterinary evaluation within 24–48 hours to differentiate between aggressive tumors and infections. Seek immediate emergency care if the mass is bleeding, painful, or if your dog is lethargic and refusing food.
What causes a rapidly growing lump on my dog?
A new mass that changes size quickly suggests high cellular activity and requires a professional diagnosis. Potential causes include:
- Aggressive skin tumors such as mast cell tumors
- Soft tissue sarcomas
- Localized infections like an abscess
- Severe inflammatory reactions
Is a fast-growing mass on my dog an emergency?
The urgency level for this situation is high. While you should schedule an evaluation within 24 to 48 hours, seek urgent care immediately if you notice the following:
- The lump is bleeding
- The mass is painful to the touch
- Your dog is lethargic or weak
- Your dog is refusing food
Why should I take a photo of my dog's lump for the vet?
Taking a clear, well-lit photo helps your veterinary team triage the mass more effectively by:
- Tracking the rate of change and assessing severity before you arrive
- Providing a visual baseline of the color, shape, and skin condition
- Allowing triage staff to prioritize your appointment
- Helping the team prepare for diagnostic tests like a fine-needle aspirate
Clinical Context (Merck Veterinary Manual)
For a rapidly growing lump on a dog's flank, consider the possibility of soft tissue sarcomas. These tumors can present with sudden onset and rapid growth. Radiography is useful to assess for osteolysis, proliferation, and soft-tissue swelling, and thoracic radiographs should be performed to rule out metastatic masses. Bone biopsy is imperative to confirm diagnosis.
Chapter: Oncology, Surgery
Source: The Merck Veterinary Manual, 11th Edition (Page 1205)