Introduction
Melanoma usually presents as a lump or bump and so usually is fairly obvious to owners. The precise diagnosis of this type of cancer requires microscopic evaluation of cells and/or tissue samples. It can be difficult even for a skilled veterinary pathologist to determine whether canine melanoma is malignant or benign. Radiographs (x-rays) are commonly used to assess whether the disease has metastasized – especially whether it has spread to the lungs.
Diagnosing Melanoma in Dogs
The first part of any diagnosis is a complete veterinary physical examination. Normally, the initial data base will include taking blood and urine samples. The results of these tests may reveal systemic disease and often can help identify other health conditions that may exist.
A very common diagnostic procedure used in suspected cancer cases is a “fine needle aspirate,” commonly called a “FNA” in veterinary circles. This procedure involves inserting a needle into the suspicious area and pulling back on the attached syringe to gather cells from the affected area. This procedure is almost painless – no different than an injection or a routine blood draw. The sampled cells are put onto a glass slide and then examined under a microscope. They may be dyed or stained before this examination, to help enhance particular cell types.
If the results of the fine needle aspirate are inconclusive, or if they are suggestive of melanoma, normally a biopsy of the suspicious mass will be taken. A biopsy involves taking a “chunk” of tissue, rather than just sampling cells, and usually is done under sedation or even general anesthesia. The biopsy sample will be sent to an outside laboratory for evaluation.
Additional diagnostic tests include thoracic radiographs (chest x-rays) to determine if the cancer has spread to the lungs, a fine needle aspirate of nearby lymph nodes to determine if the cancer has infiltrated the lymphatic system, and an ultrasound examination to assess whether any other areas of the dog’s body have been affected by cancer.
Diagnosing melanoma in dogs is an evolving science, or perhaps an art… It is difficult for veterinarians to identify the precise stages of malignant melanoma or to catch the subtle changes in cells or tissue that happen when melanoma transforms from benign to malignant. Because of these difficulties, most veterinarians opt to surgically remove any skin mass, whether or not it is known to be “malignant.”