Whenever you see or feel a mass on your dog it is important to have it checked out by a veterinarian. The most common tumor on older dogs is called a lipoma or fatty tumor. These are accumulations of adipose tissue in the subcutaneous layer that is slow growing. They usually expand into an area instead of invading into tissue like a malignancy. They are most commonly found on the trunk and abdomen but can occur anywhere on the body. Lipomas are not in themselves painful but can sometimes grow quite large and restrict movement especially if they are located in the armpits or inguinal areas.
Surgery is often necessary to remove the large bothersome lipomas with minimal complications. The fatty tissue is often encapsulated and is easily shelled out of the muscle layers. The surgeon will occasionally have to install drains to prevent fluid from accumulating in the space created by removing large pendulous lipomas. It is, of course, best to remove lipomas when they are smaller. There are cases where the lipomas actually are invasive and infiltrate into the muscles and nerves. These aggressive lipomas can compress areas and cause damage to the adjacent structures. The surgeon will have to dissect away these fingers of fat to try to remove as much as possible. These infiltrative lipomas may return over time.
It is best to have any skin tumor evaluated by your veterinarian. Lipomas are soft, feel uniform, and are encapsulated. A simple aspiration of the lump with a needle and syringe will occur in the exam room and the material will be placed on a slide. Examination of the thin film of cells under the microscope will reveal if the tumor is just fat cells or a malignancy. The big worry is to rule out mast cell tumors that can mimic the look and feel of lipomas and can be found within lipomas. These are the most malignant skin cancers of dogs and need to be widely excised to prevent spread to local lymph nodes. Once mast cell tumors invade the lymph nodes they may spread to the spleen, liver and bone marrow.
There are rare instances where lipomas grow within body cavities, especially the abdomen. They can grow to become enormous, space-occupying tumors that put pressure on the organs. These cases are usually diagnosed with radiographs or ultrasound. Surgery is again the best approach to remove even the large internal tumors. These patients usually go on to do just fine but there is the possibility of recurrence.
Lipomas are so common that some older dogs will have several tumors that are slow-growing and do not require surgery. In these cases we map them out in the record and the owners monitor for growth and changes. Mast cell tumors can suddenly increase in size and become red and hairless. Owners are instructed to keep track of any changes in size or appearance and be sure have rechecks on suspicious tumors. It is a good idea to have skin tumors checked out during the annual exam. However, if a mass is growing quickly and appears to be breaking through the skin, a trip to your veterinarian is recommended sooner than later.