Most skin tumors are first identified by the dog’s owner, when they either see a lump or feel it while petting or grooming their companion. Occasionally, skin tumors are identified by a veterinarian incidentally as part of a routine physical examination. Skin lumps and bumps can be something as simple as a pimple or an allergic reaction to an insect bite. On the other hand, some skin masses are much more serious. Wise owners will have their dogs examined by a veterinarian to assess the significance of any skin tumors that they detect. The veterinarian will gather detailed historical information from the owner, including how long the mass has been present, whether it has changed in shape or size and, if so, whether it changed rapidly or slowly, whether the dog has been scratching or licking at the lump and whether the dog has suffered any recent trauma. The doctor will conduct a thorough physical examination of the dog, paying particular attention to any other skin masses.
Skin tumors are usually first analyzed by a fine-needle aspirate, an impression smear or a scrape or a swab sample. A fine-needle aspirate involves gently inserting a needle into the lump, pulling back on the stopper of the attached syringe and then squirting any extracted fluid and cells onto a glass slide for examination under a microscope. This is a quick and easy way to diagnose many skin tumors, especially benign fatty tumors called lipomas. Another useful diagnostic tool is an impression smear. This simple procedure involves pressing a glass slide onto the surface of the mass and then examining the transferred cells under the microscope. A scrape or swab sample is another way to transfer tumor cells onto a glass slide. A skilled veterinarian can identify many types of tumors from microscopic assessment of cells by these various methods, reaching at least a tentative, or sometimes even a definitive, diagnosis.
Often, however, a somewhat more complicated technique, called an incisional “biopsy,” is required to accurately diagnose the tumor type. An incisional biopsy involves surgically removing a small piece of the mass and some of the normal tissue surrounding it. Biopsies require sedation and local anesthetic at a minimum, and occasionally require general anesthesia. Sometimes, the attending veterinarian will elect to surgically remove the entire mass – called an “excisional biopsy” - rather than taking only a piece of it. There are pros and cons to performing an incisional or an excisional biopsy, which the veterinarian can discuss with the dog’s owner. If the suspicious mass is thought to be malignant, the surgeon usually will try to remove the entire tumor and also remove a fairly wide margin of normal, non-cancerous tissue surrounding it. Biopsy samples will be packaged and sent to a laboratory, where skilled veterinary pathologists will analyze the tissue microscopically and hopefully arrive at a definitive diagnosis. Of course, it is not always possible to remove a tumor and enough nearby normal tissue to be sure that all cancerous cells have been excised. This is especially true of masses on the face and lower limbs, where there often is not enough skin around the tumor to get the wide margins that veterinary surgeons hope for.
It is important for the medical team to know exactly what type of tumor they are dealing with, so that they can come up with the best management and treatment protocol for their patient. Fortunately, current diagnostic techniques are usually quite successful in identifying the cellular composition of skin tumors.