Malignant tumors of the skin result from uncontrolled cell growth and are able to spread through the body.
Malignant tumors may occur in all areas of the body. Some forms occur primarily on the limbs, the lower back, and the head. Generally, tumor diseases become more likely the older the dog is. Malignant tumors often develop in dogs older than eight years. Smaller knots are usually discovered when owners are petting or combing their pets. Larger knots and swellings are mostly visible to the naked eye. In contrast to benign tumors, malignant tumors often exhibit faster growth. Furthermore, they are often not very distinguishable from the surrounding tissue and are not easily moveable. In the beginning, these kinds of tumors are often not much bigger than a cherry pit. Some malign tumors grow only insignificantly bigger. For example, mast cell tumors, called mastocytomas, generally do not grow to large, oversized proportions. On the other hand, other types of malign tumors, such as fibrosarcoma, can grow considerably in their development.
All body cells are normally subject to the mechanism of controlled growth. If this control mechanism is impaired, cells may grow excessively and form a lump. The underlying causes can include: radiation, injected medication, poisoning, prolonged tissue damage or genetic predisposition. However, in many cases the exact cause of a tumor cannot definitely be identified. The characteristics of malignant tumors are that they grow into the surrounding tissue and infect it. Furthermore, these types of tumors release infected daughter cells into the blood and lymph channels, and as a result they can possibly infect other areas and organs of the body. Commonly areas affected by metastases are lymph nodes and the lung. Tumors are differentiated by the kind of tissue they are formed from: from fat tissue, connective tissue, immune cells. Common malignant tumors among dogs are fibrosarcomas and mast cell tumors/mastocytomas. For more detailed information on different forms of malignant tumors see the related diseases section.
Whether a tumor is malignant or benign can only be determined by a thorough examination of a tissue sample. For this procedure a small piece of the tumor is extracted and analyzed in the laboratory. The characteristics of different tumor cells can be determined with a microscope. If the analysis classifies the tumor as malignant, oftentimes an immediate surgical removal of the tumor is necessary. The sooner the tumor is detected and treated the higher the chances of the tumor not spreading to other parts of the body and the success of the treatment. In cases where tumors are already producing metastases or growing aggressively, chemotherapy is another possible treatment which has proven to be very successful, but which results in high expenditures, and is only available in special veterinary clinics.
If you encounter suspicious skin changes (see the Diagnosis and Therapy sections) call a veterinarian and schedule a consultation within the next few days or weeks.