Mast cell tumors are the most common tumors in our dogs. These tumors originate from mast cells: Mast cells are cells of the immune system that can be found normally throughout the body and in almost every tissue in healthy animals. They are responsible for defense reactions, but also play an important role in allergic reactions. Most commonly, mast cell tumors occur in the skin and subcutaneous tissue, but internal organs such as the digestive system can also be affected.
![[Translate to English:] Golden Retriever scheinen häufiger Mastzelltumoren zu entwickeln](/fileadmin/_processed_/c/7/csm_GoldenRetriever_fb609637ef.webp)
How to detect a mast cell tumor?
Mast cell tumors of the skin appear as nodular changes. Of course, not every lump in or under the skin is a mast cell tumor, but it should be taken seriously. If you notice a thickening, lump or anything suspicious when stroking or brushing your dog, the vet should clarify the situation. Some tumors are only noticed by the vet when he palpates the dog during a routine examination or vaccination.
Whether a lump is a harmless lipoma or a mast cell tumor can never be determined with certainty simply by palpation. During a thorough work-up, the animal is first subjected to a general examination in which, among other things, lymph nodes are palpated and checked for thickening and asymmetry. A search is also made for other lumps or abnormalities. A fine needle aspiration (FNA) is then performed: A fine needle is inserted into the tumor and moved back and forth several times to remove a few cells, which are spread out on a slide. Under the microscope, after staining, it is possible to see which cells are involved and whether there are mast cells or, for example, only fat cells in the sample. If the FNA is positive, i.e. if mast cells are detected in the sample, a biopsy may be useful. This involves taking a tissue sample from the tumor, which is examined in the laboratory to determine the aggressiveness and other characteristics of the tumor.
It is often reported that the size of a nodule changed very quickly several times. One day there was a clear, noticeable thickening, which then appeared to have disappeared completely. These changes are typical for mast cell tumors and are caused by the messenger substances that are released from the tumor cells. The main role here is played by histamine from the granules of the cells.
Sometimes these areas are hairless, reddened and show signs of inflammation, especially after manipulation. These symptoms are summarized as Darier's signs. Particular care should be taken with open, ulcerated mast cell tumors!
FAQ: What to do if your dog has a lump?
A diagnosis should be made as early as possible whenever a new enlargement of the circumference is palpated. In order to differentiate between a benign tumor such as a lipoma and a malignant mast cell tumor, a fine needle aspiration (FNA) can be performed. This examination is quick, simple and almost painless and a mast cell tumor can be diagnosed very reliably.
Mast Cells
Mast cells are important cells of the immune system that are found throughout the body and in almost all tissues of healthy animals. Their main function is to enable defense reactions, but they also play an important role in allergic reactions. Degenerated mast cells have the ability to form tumors. The mast cell is so named because under the microscope it looks fattened. They contain granules, small vesicles in which messenger substances such as histamine and heparin are stored. If these granules empty, inflammatory reactions with swelling, redness and pain occur in the surrounding tissue. As this reaction takes place within a very short time, it is referred to as an immediate reaction.
Mast cell tumor: always malignant?
Mast cell tumors in dogs represent a broad group of tumors that show varying degrees of aggressiveness. If left untreated, they can increase their aggressiveness. Basically, we divide tumors into different groups, so-called grades. Depending on the system, a distinction is only made between low-grade and high-grade (Kiupel) or grade 1, grade 2 and grade 3 (Patnaik). First-grade mast cell tumors are less aggressive tumors, i.e. they only infiltrate the surrounding tissue to a minor degree and rarely form metastases. In contrast, a third-degree mast cell tumor is highly aggressive, infiltrates the surrounding tissue and forms metastases in 50%-90% of cases. It is important for the prognosis and the selection of the right therapy that the grade of the tumor is known. Many pathologists use both systems in parallel and give the grades according to both Kiupel and Patnaik.
Grading can be done on the basis of a biopsy or in the tumor material sent in. The vet can also request a more precise differentiation if necessary. A special examination of the material can detect different mutations or determine cell division markers.
While grading describes the aggressiveness of the primary tumor, staging involves searching for metastases. This involves, for example, fine needle aspiration of the regional lymph nodes. In addition, an ultrasound examination of the abdomen with puncture of the liver and spleen should always be carried out.
How can a mast cell tumor be treated?
The treatment of the mast cell tumor depends on the aggressiveness and any metastases already present. A highly aggressive tumor must also be treated aggressively. A large-scale removal of the tumor is performed with a 2-3 cm safety margin in the healthy tissue and one or two fasciae in depth. If surgery is performed, the removed tumor material should always be sent for histopathological examination, even if an FNA and biopsy have already been performed. The benefit of this examination is usually much higher than the costs.
Whether an operation is performed directly or a biopsy first depends on the localization. In the case of tumors on the legs, it is often only possible to perform a marginal surgical removal without a safety margin in the surrounding tissue, which is why a biopsy is not performed in many cases.
In the case of a mast cell tumor in the chest area, a biopsy can be taken first for better surgical planning. Surgery is then performed depending on the degree or aggressiveness of the tumor. If large-scale removal is not possible, local tumor control can be improved by additional radiotherapy. This adjuvant radiotherapy is mainly used in the area of the limbs, as a large safety margin is rarely possible with surgery. If metastases are suspected or if there is a high risk of metastasis, a chemotherapeutic agent is administered. If the tumor is already very large at the time of diagnosis or has metastasized extensively, palliative radiotherapy combined with chemotherapy is the treatment of choice.
What is the prognosis for a mast cell tumor?
If a mast cell tumor is detected early and treated optimally, the prognosis is good and life expectancy is high. In many cases, life expectancy is not affected by the tumor at all. The average survival time for a tumor with low aggressiveness (grade 1 and grade 2, low-grade) is 3-5 years if the tumor was removed with a sufficient safety margin and other treatment options were combined with surgery if necessary. A recurrence often occurs if the tumor could be removed with a small safety margin or not completely. Recurrences are always more difficult to treat and are associated with a poorer prognosis. With the aggressive form of mast cell tumor (grade 3, high-grade), the prognosis is more cautious than with the other forms. If the tumor has not yet metastasized, the prognosis is still favourable if all three pillars of tumor therapy (surgery, radiotherapy, chemotherapy) are used optimally. Existing metastases are a negative prognostic factor. In some of these cases, a poor prognosis and a life expectancy of a few weeks to months must unfortunately be assumed. Palliative radiotherapy in combination with chemotherapy can extend this to several months to a year.
In which breeds do mast cell tumors occur particularly frequently?
Mast cell tumors are more common in brachycephalic breeds such as pugs or French bulldogs. These dogs can even suffer from several mast cell tumors at the same time or develop several mast cell tumors in the course of their lives. However, these mast cell tumors are often grade 1, i.e. less aggressive. Other predisposed breeds include Labrador Retrievers and Golden Retrievers, Weimaraners and Vizsla.
