Canine histiocytic sarcoma (HS) is a highly aggressive malignant tumour that arises from histiocytic cells. Histiocytes are cells that play a crucial role in the immune system by engulfing and digesting foreign substances, such as bacteria and viruses, as well as old or damaged cells. HS can develop in various organs, including skin, lymph nodes, spleen, liver, lungs, bone, and central nervous system. The disease is commonly observed in certain breeds, such as Bernese Mountain Dogs, Flat-Coated Retrievers, Rottweilers and to a lesser extent miniature Schnauzers. HS can present with multiple variants which could either be a localised form such as around a joint or arising from other locations like the lungs, brain or multiple organs.

1. Histiocytic Sarcoma arising near a joint:

Periarticular histiocytic sarcoma (PAHS) is a type of HS that affects the tissues surrounding joints, such as tendons, ligaments, and synovial membranes. PAHS is more commonly observed in large-breed dogs, such as Flat-Coated Retrievers and other breeds. The disease typically presents as a firm, non-painful mass that is located close to a joint. PAHS can cause severe lameness and joint dysfunction, and can also spread (metastasize) to other parts of the body, such as lymph nodes and lungs. Before we suggest the best treatment options for a PAHS we should assess with further tests if the disease is localised or there is spread elsewhere in the body.

2. Disseminated Histiocytic Sarcoma:

Disseminated histiocytic sarcoma (DHS) is a type of HS that affects the internal organs, such as the spleen, liver, and lymph nodes. DHS is commonly observed in Bernese Mountain Dogs, Rottweilers, and Flat-Coated Retrievers. The disease typically presents with non-specific signs, such as lethargy, anorexia, vomiting, and weight loss. DHS is highly aggressive and can metastasize to other organs rapidly. The prognosis for DHS is generally poor, with a median survival time of less than six months. Another subtype of histiocytic sarcoma is Haemophagocytic Histiocytic Sarcoma with similar behaviour to the DHS and usually poor prognosis.

Less frequently histiocytic sarcoma can arise from other locations like the brain or the lungs. In these cases, the type of treatment depends on the extension of the disease and the presence or lack of spread.

Treatment:

The treatment of canine HS depends on the location, extent, and stage of the disease. Surgical resection is the primary treatment for localised tumours, such as PAHS, followed by chemotherapy in most cases. As in some cases surgery cannot ensure clean margins (or surgery is not an option) then radiotherapy on the primary tumour (or the scar) alongside oral chemotherapy can be considered.

In cases of DHS and HHS, chemotherapy is the mainstay of treatment. Chemotherapy drugs, such as lomustine and doxorubicin, have shown moderate efficacy in prolonging the survival of dogs with HS. However, the response to chemotherapy is highly variable, and not all dogs respond to treatment.

Chemotherapy in dogs is well tolerated in most cases and any side effects are usually mild and easily managed at home with supportive treatment. Our aim in treating your pet is to improve or maintain quality of life. Your oncologist will discuss any specific risks for your pet in the initial consult.

Radiation can also be a nice treatment for histiocytic sarcoma, which is non-resectable or where surgery is declined, or in patients with tumour spread. Radiation can  provide pain relief and shrink tumours down to improve mobility and hence the quality of life

Prognosis:

The prognosis for canine HS depends on several factors, such as the location, extent, and stage of the disease, as well as the response to treatment. The prognosis is generally poor for dogs with DHS and HHS but is considered better for localised histiocytic sarcoma such as periarticular without any evidence of spread at the beginning and some patients can live for a year or longer with appropriate treatment.

If you have any further questions, please do not hesitate to contact the hospital.