Issue Description A histiocytoma in the dog is a benign tumor.
It is an abnormal growth in the skin of histiocytes (histiocytosis), a
cell that is part of the immune system.
Histiocytic Disorders A histiocyte is a differentiated tissue cell
that has its origin in the bone marrow. The source for histiocytes is
the monocyte/macrophage line. Monocytes (found in the blood) and
macrophages (found in tissue) are responsible for phagocytosis
(ingestion) of foreign material in the body. Langerhans cells are
dendritic cells found in the skin and function by internalizing
antigens (foreign particles) and presenting them to T cells. They
arise from monocytes. Histiocytic disorders refer to diseases that are
caused by abnormal behavior of these cells.
They include the following:
Reactive Diseases of Langerhans Cells
Reactive Diseases of Macrophages
Hemophagocytic syndrome - a condition where
macrophages phagocytose myeloid and erythroid precursors (similar to
hemophagocytic lymphohistiocytosis in humans)
Malignant Diseases of Langerhans Cells
Malignant histiocytosis - a condition found
in Bernese Mountain Dogs
Diffuse histiocytic sarcoma
Localized histiocytic sarcoma
Malignant Diseases of Macrophages
Common Breeds At Risk
Symptoms Most commonly histiocytomas are found in young
dogs and appear as a small, solitary, hairless lump, although Shar
Peis may be predisposed to multiple histiocytomas. They are most
commonly found on the head, neck, ears, and limbs, and are usually
less than 2.5 cm in diameter. Ulceration of the mass is common.
Diagnosis Definitive diagnosis is established via
cytology or biopsy. Your veterinarian may want to wait and watch the
lump, based on the age of your dog and the location and presentation
of the lesion. Histiocytomas will spontaneously regress in 2- 3
months. If in doubt, biopsy will provide an answer as to the nature of
Treatment Most histiocytomas will regress within two or
three months. Surgical removal may be necessary if the tumor does not
regress or if it is growing rapidly to a large size. Histiocytomas can
also be treated with an intralesional injection of a corticosteroid,
but this is not always successful.