This tumour type can occur locally, but also spread. If local, it most often occurs in the skin and subcutaneous tissue of the extremities. Since these cells occur in many places in the body, this tumour can be found in almost any place in the body. This tumour type has already been reported in the following locations: lungs, lymph nodes, liver, spleen, stomach, pancreas, tissue between the lungs, skin, skeletal muscle, central nervous system (= brain and / or spinal cord), bone, bone marrow, nasal cavity and eyes.

Behaviour

Histiocytic cells are cells of the immune system responsible for cleaning up the remains of dead cells. These cells can degenerate and start to multiply uncontrollably, forming a tumour. Either a histiocytic sarcoma will occur in a single organ or spread over multiple organs. This tumour type is locally invasive and local spread to the draining lymph nodes is possible. Both the local and dispersed form have the potential to behave very aggressively.

Prevalence

Histiocytic sarcomas usually occur in middle aged dogs or older, but can also occur at the age of 3.

Breed predisposition

This tumour type occurs more in Bernese Mountain Dog, Flat-coated retriever, Golden retriever, Labrador retriever, Rottweiler than other breeds. The location near the joint is most commonly reported in Rottweilers and Flat-coated retrievers.

Symptoms

Depending on where the tumour is located, it can cause different symptoms. For example, a tumour in/near the mouth can explain a decreased appetite or mouth bleeding and one in/near the intestines diarrhea. In general, nonspecific symptoms are present: lethargy, loss of appetite, weight loss. One can also notice a growth, limping, coughing, vomiting and swollen lymph nodes.

Histology

By piercing the tumour and staining a sample of tumour tissue, the veterinarian can estimate the tumour type. This is important as this tumour type can closely resemble other tumours whose recommended treatment and prognosis are very different. One can already get an idea about the tumour type based on the shape, content and color of the cells. In addition, staining specific for macrophages distinguishes this tumour type from a lymphoma (CD18 is carried 10x more by macrophages on the cell surface than by lymphocytes (the cell type that makes up a lymphoma)).

Staging

Because the tumour can occur in several places (simultaneously), complete staging is recommended.

• Blood test: this tumour type regularly causes anomalies in blood tests. Anemia is common, as well as a high white blood cell count, low platelet count, increased liver enzyme count, low blood protein (albumin) and low cholesterol levels, while excess calcium levels are rare.
• Imaging: abnormal growths can be detected via radiography of the chest cavity and ultrasound of the abdominal cavity.
• Bone marrow sample: a bone marrow sample may be appropriate to check whether the tumour has spread to the bone marrow. The cells from this sample can be examined under the microscope or further examined via the lab.

Surgery

Surgery can be used as treatment method when no metastases are present. If the tumour is only locally present, the combination with chemotherapy and radiation could further extend the survival time.

Chemotherapy

If metastases are present, chemotherapy can be used. CCNU chemotherapy (which contains the substance lomustine) is said to be the most efficient to date for histiocytic sarcomas (most is known about this, but this does not exclude that other chemotherapeutic options may also have good effects).

Radiotherapy

The efficacy of RT against histiocytic sarcoma has not been fully studied. However, preliminary evidence suggests that this tumour type is radiosensitive. Dogs treated with radiation survived a median of 182 versus 60 days for those that were not.

The disease course of widespread histiocytic sarcomas is rapid and fatal if not treated. Unfortunately, even with treatment, the median survival time is short. In the local form of the condition, the disease proceeds more slowly. There have been reports of 6-month to one-year survival with treatment.