Understanding Cancerous Lumps in Dogs: What Pet Owners Need to Know
As pet owners, discovering a lump or bump on your dog can be alarming. One of the most frequent concerns is whether these growths are cancerous. Fortunately, not all lumps mean cancer, but it is essential to understand the diagnostic steps, notably the role of biopsy, to determine the nature of these growths.
How Common Are Cancerous Lumps in Dogs?
Studies and veterinary experience suggest that roughly 20% of dog lumps are cancerous. That means about 4 in 5 masses are benign, including conditions such as lipomas (fatty tumors), cysts, or inflammatory reactions. However, distinguishing benign from malignant growths without microscopic examination is virtually impossible.
What Is a Biopsy and Why Is It Performed?
A biopsy is a vital diagnostic procedure in veterinary medicine. It involves removing a small sample of tissue or the entire lesion for examination under a microscope by a veterinary pathologist. Biopsies help:
- Differentiate between benign and malignant tumors
- Identify inflammatory, infectious, or autoimmune conditions
- Guide treatment planning and prognosis
Veterinarians use biopsies to confirm whether a suspicious lump is cancerous, what type of cancer it may be, and how aggressive it is.
Different Types of Biopsies in Dogs
- Fine Needle Aspiration (FNA): A simple, minimally invasive technique used to collect cells for cytological examination.
- Punch Biopsy: Circular blades remove skin samples, often used for dermatological diagnoses.
- Wedge Biopsy: A V-shaped section, including deeper tissue layers, sampled from the transition between normal and abnormal tissue.
- Shave Biopsy: Removes only the upper layer of the skin to assess surface-level abnormalities.
- Excisional Biopsy: Removes the entire mass, useful for small, well-defined lumps.
- Jamshidi Needle Biopsy: Typically used for sampling bone lesions while avoiding surgical complications.
- Surgical Biopsy: Includes incisional (partial) or radical removal, often requiring general anesthesia.
When Should a Biopsy Be Considered?
Veterinarians recommend biopsies for:
- New, rapidly growing, or non-healing lesions
- Lumps with abnormal color or texture
- Persistent skin conditions unresponsive to treatment
- Areas that are painful, ulcerated, or causing systemic symptoms
Preparing for a Biopsy
Before the biopsy, the area may be partially clipped, avoiding full shaving to preserve diagnostic skin features like crusts or scaling. Depending on the site and technique, local anesthesia, sedation, or general anesthesia may be administered.
What Happens to the Biopsied Tissue?
Once removed, the tissue is fixed in formalin and sent to a pathology lab. It is processed, stained, and examined microscopically. If needed, additional techniques such as immunohistochemistry help differentiate between tumor cell types. Biopsy reports include:
- Microscopic description
- Definitive diagnosis or differential diagnoses
- Tumor type and grade
- Mitotic index and cell morphology
These findings help determine if additional treatments like surgery, chemotherapy, or radiation are necessary.
Risks and Limitations of Biopsy
While generally safe, biopsies carry minor risks such as:
- Bleeding or bruising
- Pain or discomfort
- Infection at the biopsy site
- In rare bone biopsies, risk of pathological fracture
Occasionally, biopsy results may be non-diagnostic due to miscollection, necrotic tissue, or sample degradation.
Post-Biopsy Care and Follow-Up
After the procedure:
- Pain management is provided
- The site is monitored for signs of infection or dehiscence
- Activity is restricted until healing is complete
- Sutures are usually removed within 10–14 days
Results take about 1–2 weeks. Depending on the findings, the veterinarian will suggest next steps, such as complete removal of the tumor or additional tests.
To Biopsy or to Excise?
Sometimes, if the lump is small and entirely resectable, the veterinarian may opt for direct excisional biopsy to remove the mass completely instead of performing a preliminary biopsy. This is typically done when the diagnosis alone would not change the treatment plan.
Conclusion: Don’t Panic, But Don’t Ignore Lumps
While only about 20% of dog lumps are cancerous, owners should not dismiss any new or changing lumps. A biopsy remains the gold standard for determining the exact nature of abnormal tissue in dogs. It helps guide therapy, predict outcomes, and potentially save your pet’s life. If you notice unusual lumps on your dog, consult your veterinarian promptly to discuss whether a biopsy is warranted.
