Canine Histiocytomas

A histiocytoma is a benign skin tumor that originates in the Langerhans cells, immune cells that function to provide protective immunity to the tissues that are in contact with the outer environment -- the nose, stomach, intestines and lungs, but mainly the skin's surface. These cells are also referred to as dendritic cells, and histiocytes.

Canine histiocytomas are common, benign, cutaneous neoplasms. The incidence rate for histiocytomas drops significantly after 3 years, although dogs of all ages may be affected. They occur in all breeds, but purebred dogs are predisposed, particularly Boxers and Dachshunds. Lesions may occur in any region of the body, but are frequent on the head, particularly the pinna. Canine histiocytomas are typically solitary, dome shaped growths with complete or partial alopecia, and are usually smaller than 2.0 cm in diameter. They display a range of cytological features with a variable, but often high mitotic index, and tend to be progressively infiltrated by lymphocytes, undergoing spontaneous regression within two or three months. Histiocytomas arise in the dermis and may invade the epidermis in some cases. Surgical removal may be necessary if the tumor does not regress or grows rapidly to a large size. Multiple histiocytomas occur rarely, and the recurrence rate for histiocytomas at surgical excision sites are extremely low.

 FNA of a cutaneous histiocytoma of a 7 years old Boxer. Quick-stain

A classic example;

Fine needle aspirate of a dermal mass on the dorsal tail of a 7-year-old, spayed female, Boxer. The round cells had the typical morphology of histiocytes with discrete cell borders, and a moderate amount of light basophilic cytoplasm with a round or oval eccentric nucleus that had finely stippled chromatin with one or two occasional nucleoli. Mitotic figures were occasionally seen within this population. A scant population of small, well-differentiated lymphocytes was also appreciated admixed with these cells.

  FNA of a cutaneous histiocytoma,Two mitotic figures and a bi-nucleated cell in this field. Quick-stain

FNA of a cutaneous histiocytoma, Two bi-nucleated cells in this field. Quick-stain

Source: American Society for Veterinary Clinical Pathology