Equine giant cell tumor of soft parts: a series of 21 cases (2000-2007).

This study investigates giant-cell tumors in horses, a rare condition mostly found in the hind limb tissues of older horses. The study, conducted in Colorado from 2000 to 2007, tracked 21 cases, noting occurrences particularly in male horses aged 10 years or more. The tumors displayed specific markers suggesting their origin and the effectiveness of surgical removal was also evaluated.

Research Subjects

• The study focused on 21 documented cases of equine giant-cell tumors.
• Most cases occurred in male horses aged 10 years or older, suggesting the condition is more common in older male horses.
• Nearly half of the tumors (43%) were found within the hind limbs, indicating these areas as the most probable for tumor development.

Characteristics of Tumors

• The tumors displayed key histological features such as multinucleated giant cells and hemosiderin-laden macrophages mixed with spindle-cell proliferation.
• Most tumors indicated changes related to liposarcoma, variable areas of necrosis and hemorrhage, and intermediate numbers of mitotic figures.

Origins of Tumors

• Immunohistochemical results suggested two distinct cell populations within the tumors: vimentin-expressing neoplastic mesenchymal cells and CD18 (a histiocytic marker) expressing multinucleated giant cells.
• These results imply that the tumors originate from mesenchymal tissues with possible recruitment of a secondary histiocytic population.

Treatment and Follow-up

• Surgical excision was attempted for most horses and in most cases was considered clinically complete.
• A recurrence of the tumor was reported in one horse and one mule after surgery.
• In 18 horses, surgery appeared successful with no recurrence of the tumor, regardless of whether all tumor margins were removed.
• Unfortunately, nearly half the horses (10 out of 21) could not be followed-up within approximately 3 months after surgery, hindering the evaluation of long term outcomes.
• Out of the 11 horses that were available for follow-up, none showed evidence of metastasis.

Future Research

• The authors suggest that a larger study with controlled follow-up is needed to better understand the potential malignancy of these tumors and the importance of complete surgical excision.