Giant Cell Tumors in Cats

Malignant Fibrous Histiocytoma in Cats

Histiocytes are white blood cells that reside within the connective tissue of the body. Referred to as tissue macrophages, histiocytes play a defensive role in the body’s immune response, engulfing cellular debris and infectious agents, as well as initiating defense mechanisms in the system. The term histiocytoma refers to a tumor containing an excessive number of histiocytes.

Generally, histiocytomas are benign growths, but there are documented cases of malignant fibrous histiocytomas, where the tumor is composed of both histiocytes and fibroblasts. Fibroblasts are the most common cells found in the body’s connective tissue, playing a major role in wound healing. This condition involves the cells of both, with the addition of giant multinucleated cells, which occur as the result of the immune system cells attacking infectious agent cells and fusing together.

This category of giant cell histiocytoma is found mainly in cats, although it can occur in any animal breed.

Symptoms and Types

The most common symptoms include:

  • A firm and invasive tumor in the fat layer of the skin
  • Lack of appetite
  • Weight loss, often rapid
  • Lethargy


The causes for malignant fibrous histiocytoma are currently being studied.


Upon examination, your veterinarian will need to rule out a variety of other medical issues prior to issuing a diagnosis and treatment plan. Other medical conditions that can cause giant cell tumors to form include:

  • Fibrosarcoma - a malignant tumor located in the fibrous tissues
  • Chondrosarcoma - a tumor that can be found in the cartilage of the body
  • Liposarcoma - a tumor that develops in the fat cells of the body
  • Peripheral nerve sheath tumors

Your veterinarian will take a sample of the suspect tissue for biopsy so that the exact composition of the tumor can be ascertained. A histological examination, along with x-ray imaging, will define the course of treatment.

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