Oncology Update: Clinical Approach to Cutaneous and Subcutaneous Masses

Toronto veterinarian

Oncology Update

Central Toronto Veterinary Referral Clinic
Kevin Finora DVM, Diplomate ACVIM (Oncology and Small Animal Internal Medicine)

Clinical Approach to Cutaneous and Subcutaneous Masses

Clients, as concerned pet owners, love to ask us questions. One question we hear often is, “I found this lump, should I worry about it?” In almost every case the answer to that question should be, “Let’s investigate and find out!”

One thing we, as veterinarians, should never do is ignore a cutaneous or subcutaneous mass. Approximately 40% of all cutaneous masses in dogs are malignant and approximately 50% of all cutaneous masses in cats are malignant. A wide body of literature has repeatedly demonstrated palpation to be the least sensitive and specific method by which to determine the etiology of a mass. It is important to remember that many malignant tumours, mast cell tumours in particular, may feel soft. Many times this “soft” feel leads to a presumptive diagnosis of a benign mass, such as a lipoma. Such a conclusion has no basis in scientific fact, soft does not equal benign. How a mass feels does not correlate with biologic behaviour. Our fingers are not microscopes and nothing can replace the accuracy of microscopic evaluation (cytological or histological) in determining the etiology of a mass. Armed with a microscopic evaluation, we are better able to determine how concerned we should be about the mass in question.

When a mass is discovered a Five Step Approach is recommended:

  1. Record the location of the mass on a body mass map
  2. Measure the mass with callipers and note the size and date on the mass map
  3. Aspirate the mass
  4. If the mass is fat (i.e. a lipoma) note the diagnosis
  5. The mass should be re-aspirated on a yearly basis or sooner, if the character or size of the mass changes

The recommendation for re-aspiration of the mass is based on the well-documented phenomenon of malignant transformation. Malignant transformation is the process by which a previously benign tumour acquires cancerous properties and transforms into a malignant tumour. Any chronic inflammatory process, as could be present at the periphery of a benign mass, such as a lipoma, can be a malignant trigger. Malignant triggers can initiate the transformative process. Mast cell tumours are well known for demonstrating malignant transformation.

If a mass is not a lipoma, the next diagnostic step depends on the cytology. If there is a suggestion or suspicion of neoplasia, then a biopsy is recommended. When a biopsy is planned it must be taken with an idea of how the mass will later be definitively removed, if necessary. This pre-biopsy consideration is essential because the entire incisional biopsy tract must be removed with the excisional surgery. There is always a risk neoplastic cells can be “dragged” through normal tissues during incisional biopsy and care must be taken with excision to ensure all possible affected tissue is removed.

Biopsy prior to mass removal will allow for appropriate margins to be obtained. Not all tumours require the same surgical margins to be taken. For example, feline injection site sarcomas need 5cm, mast cell tumours 3cm, while a lipoma needs only a close margin. Once the diagnosis is known, the appropriate surgery can be planned.

This diagnostic approach will ensure a careful watch is kept on all cutaneous and subcutaneous mass and appropriate action is taken as soon as possible. The sooner and more completely we act, the more likely we are to have a successful long-term outcome.

Dr. Kevin Finora is a Board Certified Oncologist and Small Animal Internist who is part of the Healthcare Team at the Central Toronto Veterinary Referral Clinic. He is available for referrals and consultations Monday to Thursday (including Monday and Tuesday evenings). Please contact him with any oncology questions or concerns.

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Categorised as: Oncology

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