Pathogenesis of metastatic bone tumors

Metastatic bone tumors are mainly produced through two pathways: lymphatic or blood. Malignant tumors in any organ throughout the body can be metastatic to bones through the blood circulation or lymphatic system. So, what is the pathogenesis of metastatic bone tumors?

The main route for extra-bone malignant tumors to metastasize to bones is through the blood circulation system, and a few through the lymphatic system. For example, breast cancer can infiltrate the proximal humerus along the axillary lymphatic vessels. Primary tumors metastasize to bones mainly through the blood circulation system, and rarely through the lymphatic system.

1. Transfer process Generally speaking, the transfer process can be divided into 5 stages:

(1) Tumor cells shed from the primary tumor.

(2) Infiltration of tumor cells into surrounding capillaries.

(3) Tumor cells enter the blood circulation, and tumor cell emboli are formed and retained.

(4) Tumor cells escape from blood vessels.

(5) Tumor cells continue to grow in the retained bones and form metastases.

The proximal end of the limb bones is rich in blood supply and has a slow blood flow rate, so tumor cells tend to stay and grow there, forming metastatic lesions. The trunk system is prone to metastatic tumors, which may be related to the anatomical characteristics of the spinal venous system. This system is located around the dura mater and the spine, has no venous valves, and is connected to the superior and inferior vena cava. When the pressure in the thoracic and abdominal cavity increases, the blood can flow back, increasing the chances of tumor cells staying there and forming metastatic tumors.

The pathogenesis of metastatic bone tumors is a very complex, multi-step, continuous process that involves both tumor and host factors, starting with the shedding of malignant tumor cells from the primary tumor, invading and destroying adjacent tissues, entering the circulatory system, penetrating the basement membrane, infiltrating surrounding tissues, and forming metastases in target organs.

The venous system, especially the vertebral venous system, plays a major role in the skeletal metastasis of tumors. The pathogenesis of metastatic bone tumors is more likely to occur in the trunk bones, followed by the proximal femur and humerus, and less likely to occur in the distal femur and humerus.

The pathogenesis of metastatic bone tumors is also related to the location of the primary tumor. For example, breast cancer bone metastasis usually occurs in the thoracic spine and proximal humerus, and thyroid cancer is common in the cervical spine and skull. Of course, sometimes the occurrence of metastatic tumors is also unrelated to the location of the primary tumor. Metastatic tumors are mostly malignant tumors, such as primary osteosarcoma, lymphoma, and myeloma, which metastasize to the bone and invade the joints. Its pathogenesis is not very clear.