Diagnosing Melanoma in Dogs (One Vet)

Diagnosing melanoma in dogs starts with a physical examination.

• Since the primary tumor is visible, the vet will inspect its physical characteristics (swelling, ulceration, or bleeding).
• To confirm the diagnosis, the vet must perform fine-needle aspiration (FNI) and The analysis of the specimen taken with FNI is called cytology, and with biopsy – histopathology.
  • FNI and biopsy will confirm the diagnosis and then help with tumor staging. The procedure is called mitotic index – the percentage of melanoma cells undergoing mitosis (cell division) at a time.
  • It is used as a measure of how fast the tumor is expected to grow.
• To evaluate the dog’s overall health and check for metastasis, the veterinarian will perform
  • Blood tests
  • Urinalysis
  • Chest x-rays
  • Abdominal ultrasounds
  • MRI
  • CT scans. (One Vet)

What the Vets Are Looking for That Indicates Melanoma (Dog Cancer.com)

Several things on the cytology or biopsy can help a veterinarian or pathologist diagnose melanomas and predict how aggressively they may behave.

Ki-67

• Several studies have found Ki-67 to be the most reliable indicator of how aggressive a dog’s melanoma will be.¹⁶
• Ki-67 is a nuclear protein associated with rapid tumor growth and cell proliferation. Knowing if these proteins are present may help predict aggressive behavior.⁵The pathologist can see these proteins with the help of a special stain.
• A Ki-67 index greater than 15% suggests a bad prognosis.¹⁶

Nuclear Atypia

• This is when the nuclei of the cells have an abnormal appearance associated with malignancy.¹⁶Sometimes it is reported as “mild,” “moderate,” or “severe.”

Mitotic Index

• Many studies suggest the mitotic index is the most accurate way to predict aggressive behavior in a tumor.
• The pathologist looks for cells that are right in the middle of dividing, then counts how many there are in a high-powered microscopic field.²
• The sample is then given a score.
• In general, a tumor with less than three mitotic figures in a high-power field will likely express benign behavior and be less aggressive. (Dog Cancer.com)

Staging – What is Malignant Melanoma? (Wag!)

Malignant melanoma is often fatal within one year even with treatment to remove the cancer.

• The average survival time for this disease is up to about 10 months, though dogs can live up to 36 months with immediate surgical removal of the melanoma.
• The only treatment is surgery because chemotherapy and radiation are not effective.

There are four stages of malignant melanoma, and each has its own survival time.

• Stage one (smaller than 2 cm): about twelve months
• Stage two (2-4 cm): about eight months
• Stage three (larger than 4 cm or tumor that has spread): about four months
• Stage four (extensive metastasis): about one month (Wag!)