Osseous Metaplasia in the Mesenteric Lymph Node with Metastatic Cholangioadenocarcinoma in a Cow

Introduction: Osseous metaplasia in extraosseous sites associated with neoplasm is uncommon. The pathogenic mechanism remains poorly understood. Occurrence of osseous metaplasia within the lymph node affected with metastatic cancer has not been reported in detail in humans and animals yet, to the author’s knowledge.Presentation of Case: A Holstein-Friesian dairy cow, aged 8 years and 9 months, was slaughtered for food and revealed multiple neoplastic nodules in the liver and many other visceral organs and tissues. Histopathology and immunohistochemistry made a diagnosis of intrahepatic cholangiocarcinoma displaying an aggressive behavior with widespread metastasis. A mesenteric lymph node with metastatic cholangiocarcinoma had extensive areas of osseous metaplasia, exhibiting well-differentiated bone trabeculae dependent on the balance between osteoblastic proliferation and osteoclastic bone resorption. Necrotic areas in this metastatic nest underwent a response by macrophages and multinucleated giant cells in the stromal connective tissue that showed prominent fibroblastic proliferation and abundant capillaries, suggesting that high activity of mesenchymal cells resident at the lymph node was implicated in the development of bone trabeculae.Conclusion: This appears to be the first to report osseous metaplasia in the lymph node with metastatic cancer. Although a precise explanation for its formation remains to be determined, this bovine case may be useful in the future when researching human cancer associated with osseous metaplasia