What are bone metastases? How are they treated?

Author: Niu Xiaohui, Chief Physician of Beijing Jishuitan Hospital

Reviewer: Ren Dajiang, Chief Physician of the Seventh Medical Center of the General Hospital of the Chinese People's Liberation Army

Malignant tumors can occur in many parts of the body, and they often metastasize to bones through the blood system. This is what we often call bone metastasis, which is a secondary bone tumor. For patients, it is very important to understand the pathogenesis and treatment of bone metastasis.

1. Which tumors are prone to bone metastasis? Where may they metastasize?

Almost all tumors can metastasize to bones, including tumors in internal organs and muscles, and malignant soft tissue sarcomas.

The most common ones include lung cancer, breast cancer, thyroid cancer, prostate cancer, and kidney cancer. Among patients with these tumors, nearly 30% may experience bone metastasis. This number is quite large and should be taken seriously.

Figure 1 Original copyright image, no permission to reprint

But in fact, in a study conducted abroad that was able to perform autopsies, the incidence of bone metastasis of these tumors was as high as 80%. The reason why we did not discover it in clinical practice is because the patients had no symptoms. After it metastasizes to the bones, it must have symptoms to be discovered. If there are no symptoms, we may not pay any attention to it at all.

Where is the primary bone tumor most likely to metastasize? More than 90% will metastasize to the lungs, and once metastasized to the lungs, the respiratory function of the lungs will be affected. Conversely, lung cancer is also prone to metastasize to the bones, causing fractures, pain, and reduced quality of life.

For bone metastases, because they are transferred through the blood system, they are easy to metastasize to places with rich blood supply, that is, the so-called cancellous bone, such as the axial bone - the spine, and also places like the pelvis, ribs and so on.

Others are proximal bones, which are close to the heart, such as the bones in the upper thigh, which we call the proximal femur. These bones are relatively rich in blood, and tumors are more likely to metastasize.

2. What are the treatments for bone metastases?

The first thing is to remove the bone tumor and make it inactive. Whether it is chemotherapy, targeted therapy, or immunotherapy, as long as the tumor is inactive, the bone will repair.

The second thing is local treatment. One is radiotherapy, because radiotherapy can also make the tumor disappear locally, but there is a problem with radiotherapy, that is, after radiotherapy, while the tumor cells are destroyed, the normal bone cells will also be destroyed, so bone repair is also difficult; another is to remove the tumor through surgery, and the normal bone must also be removed, so reconstruction is required. So whether it is radiotherapy or surgery, there is the problem of damaging normal tissue. Of course, there are many methods in orthopedics, and the removed bones can be reconstructed by other methods.

The patient's local treatment needs to be determined based on systemic treatment and overall prognosis. If systemic treatment is ineffective, or the treatment is expected to take a long time and the patient's life expectancy is long, it is recommended to use a relatively faster method so that the patient can restore his quality of life more quickly, cooperate with further treatments, and have more confidence in the treatment. At this time, multidisciplinary collaborative treatment is needed.

Because surgery or radiotherapy can provide patients with opportunities, but otherwise, how can the bones destroyed by tumor cells be repaired?

The body has osteoclasts, because in the normal process of natural repair, osteoclasts play a certain role. Osteoclasts are normal cells, not destructive cells, and they work together with osteoblasts. It's like a renovation, someone has to tear down the old one before someone else can build the new one.

Figure 2 Original copyright image, no permission to reprint

When the tumor metastasizes, osteoclasts are controlled by the tumor and become extremely active. Now we can use drugs to inhibit the activity of osteoclasts, so this is also a method of treating bone metastasis.

3. What are the drugs for treating bone metastases and inhibiting osteoclast activity?

There are currently two types of drugs that can inhibit the activity of osteoclasts. One class of drugs is called bisphosphonates, and the other class of drugs is called RANKL inhibitors (denosumab). Although the mechanisms of action of these two types of drugs are different, they both inhibit osteoclasts.

If osteoclasts are inhibited, there will be no cells to destroy bone, and bone damage will naturally be reduced. If the tumor is also suppressed, bone repair will be improved, and drugs can be used to treat bone metastasis.

In addition, because tumors need space to grow, they also need nutrients released by osteoclasts after destroying bones, which actually indirectly limits the growth of the tumor itself, so it kills two birds with one stone.

In addition, when it is combined with anti-tumor drugs and drugs that directly kill tumors, it can achieve twice the result with half the effort in the treatment of bone metastases.