Metastatic lymphangiosarcoma in a horse.

This study reports a case of a horse suffering from a metastatic lymphangiosarcoma, identified through necropsy and histologic examination, which manifested as respiratory distress and edema. The horse also showed tumor metastases in the spleen, lungs, and kidneys.

Background

• The study illustrates the finding of a case of metastatic lymphangiosarcoma in a horse. Lymphangiosarcoma is a rare and aggressive type of cancer that starts in the lymphatic system.
• The horse was initially presented with respiratory distress and edema in the ventral thorax and abdomen—a condition called abdominal edema or dropsy. Edema is the swelling caused by excess fluid trapped in the body’s tissues.

Necropsy Findings

• The necropsy highlighted diffuse edema in the subcutaneous connective tissue, a widespread condition where fluid accumulates beneath the skin.
• Several lymph nodes—including the mediastinal, mesenteric, iliac, and renal lymph nodes—were found to be enlarged and white, featuring soft, yellowish necrotic areas. This necrosis, or cell death, reflects the profound adverse effects of the tumor.

Histologic Examination

• The histologic examination showed multiple channels and disorganized vessels lined by large polymorphic (shape-varied) cells. This finding indicates the abnormal growth and division of the cells, which is a characteristic of cancer.
• Tumor metastases were found in the spleen, lungs, and kidneys, demonstrating that the cancer had spread from the original tumor.

Immunohistochemical Evaluation

• The immunohistochemical evaluation of the tumor cells revealed positive staining for factors VIII, vimentin, and keratin, which are proteins often associated with cell development, structure, and function.
• However, laminin was scarce, and collagen IV staining was negative. These findings suggest a discontinuous or absent basement membrane in the case, denoting that the structural feature separating the epithelium, mesothelium, and endothelium from the underlying connective tissue is impaired or missing in the tumor cells, contributing to their uncontrolled growth.