Veterinary Oncology: What to Do With Lumps and Bumps on Dogs and Cats

When a dog or cat presents with a dermal or subcutaneous mass, the owner is often told, “Keep an eye on it.” But what does that mean? Keep an eye on it for how long? How much should a mass grow before it is investigated? As a veterinary cancer specialist, I hear all too often that a mass does not “look” or “feel” malignant. The truth is that even an experienced cancer specialist (like me) cannot look at or feel a mass and know what it is.

The current recommendations for working up a mass include the same generalities our clients hear: “Recommend if a mass is changing in size or appearance, or bothering the patient.”¹ Again, what does this mean? What changes are clinically significant—any? All? What constitutes patient “bother”? These kinds of measures are not enough. A standard of care is needed for skin and subcutaneous masses in dogs and cats.

I’ll be honest, it’s easy to get complacent. My oncology nurse had a pit bull, Smokey, whose medical record contained aspiration results from more than 10 lipomas. I performed and documented all those aspirations. When we found another mass, we waited to get an aspirate, because—based on appearance and Smokey’s history—we assumed it was benign. When we finally tested it, the 7-cm mass over his flank turned out to be a low-grade soft tissue sarcoma.

Proactive Detection of Tumors in Dogs and Cats

Although Smokey’s tumor was successfully removed with wide and clean margins, it highlighted for me the need for more definitive guidelines to promote early cancer detection in dogs and cats (Box 1).

It is well documented that cytologic and histologic evaluations are important diagnostic tools in veterinary oncology and that obtaining a preliminary diagnosis optimizes treatment planning. The 2016 AAHA Oncology Guidelines for Dogs and Cats summarize the tools used for diagnosis, staging, and treatment of common tumor types.² It is also recommended to evaluate masses that are growing, changing in appearance, or irritating to the patient.¹ However, at this time, no specific guidelines exist for determining when to aspirate, biopsy, or monitor canine and feline skin and subcutaneous masses.

Without guidelines to increase both public and professional awareness, superficial masses may be monitored for too long. Allowing a tumor to grow can turn what might have been a simple surgical removal into a much more complicated one. Surgical excision of larger masses may result in less than adequate surgical margins (narrow or incomplete), leading to recurrence and additional costly therapy (more aggressive local surgery, radiation therapy, and/or chemotherapy).

Even worse, the tumor may become too big or advanced to be removed or treated at all. I see this all the time. These are often the most frustrating and heartbreaking cases. In veterinary medicine, most skin and subcutaneous tumors can be cured with surgery alone if diagnosed early when they are small.

I’ve learned three things from Smokey and from my time as a cancer specialist:

• Be proactive with lumps and bumps.
• Know what a mass is before you remove it.
• Make the first surgery the only surgery.

Guidelines for Tumor Detection and Diagnosis

1. Be Proactive With Lumps and Bumps

See something: If a dog or cat has a mass that is the size of a pea (1 cm) and has been there 1 month,

Do something: Aspirate or biopsy, and treat appropriately!

Obtaining a definitive diagnosis with cytology or biopsy early and before excision will lead to improved patient outcomes for superficial masses. When smaller, superficial tumors are detected early, surgery is likely curative, especially for benign lesions and tumors that are only locally invasive with a low probability of metastasis. If a tumor is removed with complete surgical margins, the prognosis is often good with no additional treatments needed.

Although the See Something, Do Something guidelines specify a 1-cm mass, smaller masses may also be aspirated or biopsied. However, they should not be allowed to grow larger than 1 cm without investigation. Practitioners should measure and document the size of the initial mass for comparison to see growth, and educate clients about the “pea” size requirement to encourage them to have masses evaluated.

2. Know What a Mass Is Before You Remove It

Diagnosis of many skin and subcutaneous masses can be achieved with fine needle aspiration (FNA) and cytology.¹

Aspiration and Cytology

FNA and cytology provide a diagnosis for many dermal and subcutaneous masses, especially those that that exfoliate well. FNA is useful to distinguish neoplasia from inflammation and benign masses, including lipomas and sebaceous adenomas. Cellular morphology may also allow the determination of benign or malignant phenotype. For malignant tumors, cytology provides information that assists in formulating diagnostic and treatment plans.

Advantages of cytology include minimally invasive approach, low risk, low cost, and results that are available more quickly than biopsy results. The disadvantages are that results may be nondiagnostic or equivocal because of a small number of cells in the sample, poor exfoliation of the cells, or poor sample quality. In these cases, histopathologic confirmation may be required for definitive diagnosis.³

FNA may be accomplished using one of two techniques: aspiration or fenestration. During aspiration, the needle and syringe are attached, and vacuum is maintained. In fenestration, the needle alone is inserted into the mass percutaneously. Fenestration is done without aspiration, often yields more cellular material, and causes less hemorrhage.³ I personally prefer and start with fenestration as I find it easier and consistently get diagnostic samples. Aspiration is more useful for fluid-filled masses.

Unless the sample is composed exclusively of fat, clear cystic fluid, or acellular debris, it should be submitted to a trained cytopathologist. When in doubt, send it out. Including an adequate history helps the pathologist make an accurate diagnosis.

Biopsy

If cytology is nondiagnostic, a pretreatment biopsy is recommended before complete tumor removal. This biopsy will help determine the optimal treatment plan. A practical recommendation in these cases is if the lesion fits in an 8-mm biopsy punch, punch it out. If the mass is larger than an 8-mm biopsy punch, an incisional biopsy (wedge, Tru-cut, punch) is required for diagnostic confirmation before tumor removal.

Staging diagnostics are also often indicated before curative-intent surgery. Consultation with a veterinary oncologist is recommended to help in these diagnostic decisions.

3. Make the First Surgery the Only Surgery

It is tempting to remove a mass right away, and owners often say they want it removed as soon as possible. An excisional biopsy establishes a diagnosis and removes the tumor at the same time. However, this approach is not recommended for undiagnosed skin and superficial masses because surgical approaches vary with tumor type. For benign masses, marginal excision may be adequate for long-term control. In contrast, malignant tumors often require 2 to 3 cm margins.^1,4–6 When an excisional biopsy (or debulking surgery) leads to incomplete margins for malignant tumors, more treatment, more morbidity, and more expense ensue. Thus, removing the mass entirely is not recommended without a cellular diagnosis before definitive excision. Research confirms that the first surgery is the best chance for a cure.²

What Will We Find?

Primary skin and subcutaneous tumors are common in dogs and cats. While the overall incidence is difficult to determine, approximately 25% to 43% of submitted canine and feline biopsy samples are of the skin. Of submitted samples, 20% to 40% are reported to be malignant.⁷

The most common malignant skin tumors in dogs are mast cell tumors, soft tissue sarcomas, and squamous cell carcinomas. The most common benign canine skin and subcutaneous benign tumors include lipomas, histiocytomas, and perianal gland adenomas.⁷

In cats, the most common superficial tumors are basal cell tumors, mast cell tumors, squamous cell carcinomas, and fibrosarcomas. These 4 tumor types make up about 70% of all skin tumors in cats. Sebaceous gland adenomas are much less common. If basal cell tumors are excluded, the percentage of malignant skin tumors in cats is higher than in dogs, with studies reporting 70% to 80%.⁷

Summary

Visual monitoring of superficial masses is not enough. Cancer is a cellular diagnosis. It is always recommended to evaluate masses that are growing, changing in appearance, or irritating to the patient, but these guidelines are not enough. All skin and subcutaneous masses that are >1 cm and have been present for 1 month should be aspirated for cytologic evaluation. Biopsy is indicated if cytology does not provide a diagnosis.

Veterinary professionals and pet owners all must be proactive to advocate for early cancer detection. If tumors are detected and removed earlier—when they are small and with clean margins—the prognosis is often good and the patient may not require additional therapy. See something, do something!