Understanding Bone Metastasis


Nov. 10, 2009 – Bones are a common site for breast cancer metastasis. In this edition of Breakthroughs in Cancer Research, Washington University medical oncologist Katherine Weilbaecher, MD, discusses why bones are a fertile ground for cancer cells and how the use of osteoporosis drugs can strengthen bones and even decrease the number of tumor cells in bone marrow.



About one in eight women in the United States will be diagnosed with breast cancer at some point in her life. Many of these women will be cured of their disease, but for some, cancer will return. One area it is likely to spread is to the bones. On this edition of Breakthroughs in Cancer Research, we’ll talk about research that aims to decrease bone metastasis in women with breast cancer.

Host: Thanks for downloading this podcast from the Siteman Cancer Center at Barnes-Jewish Hospital and Washington University School of Medicine in St Louis. I’m Gwen Ericson. I’m talking with Kathy Weilbaecher, MD, a breast cancer specialist at the Siteman Cancer Center and a scientist who researches bone metastasis. Dr. Weilbaecher, thank you for joining us.

Weilbaecher: Thank you so much, Gwen, for inviting me to speak.

Host: First of all, tell me what exactly is metastasis?

Weilbaecher: Metastasis is when cancer cells leave the primary site where they started and move to other parts of the body. And then in those sites, they begin growing and can cause problems. For example, when the tumor cells begin growing in the bone, that can be very painful and can weaken the bone and make the bone more susceptible to fracture. If the tumor cells move to the lungs, that can make it more difficult to breathe. So when these rogue cancer cells leave the place where they started and set up shop in other places, they can cause problems in the normal functioning of those organs. And this is something that we want to prevent, and we want to aggressively treat.

Host: Tell me a little about basic bone biology.

Weilbaecher: Bones are not just to keep us standing and upright. Bones also are the source of our blood and our bone marrow and our immune system. And bones also help regulate our calcium, which is vital to the functioning of most organs and most cells in the body. The problem is that bones are also a very fertile soil for cancer cells to live, sometimes hide and to grow. In fact, it’s a favorite site of metastasis for breast cancer and prostate cancer cells.

Host: What is it about the bones that makes cancer cells want to grow there?

Weilbaecher: Many cancer cells are attracted to the bone environment. The bone environment contains many growth factors and many cells that actually support tumor cell growth. And one of those cells is the osteoclasts, which are bone-lining cells that can cause destruction of bone. And cancer cells secrete factors that stimulate and recruit these osteoclasts to do their dirty work. It’s a little bit like termites and carpenter ants. The carpenter ants chew the holes in the wood so that the termites can burrow and live.

Host: What has your research shown about how to minimize or stop metastasis and the symptoms it causes?

Weilbaecher: We and others have shown that if you administer osteoporosis medications or medications that strengthen the bone by suppressing these bone-destroying cells, that actually we can decrease the cancer-associated bone destruction, the cancer-associated bone pain, the cancer-associated bone fractures. But what’s even more exciting is some data that we and others have found that if you can use these bone-strengthening medicines, we can actually decrease the number of microscopic tumor cells in the bone marrow. This suggests that these medicines may not just strengthen the bone, but they might actually have some properties to make the bone inhospitable to cancer invasion, which is what we’re really trying to do.

Host: I understand you also found that some cancer therapies potentially increase the risk of metastasis.

Weilbaecher: We found that some of the growth factors that we use, which do a fabulous job of helping patients resist infection and really tolerate our chemotherapy much better, one of the side effects of some of these growth factors can be that they can stimulate osteoclast activity and can weaken the bones. In addition, some of the wonderful medicines that we have to treat prostate and breast cancer by blocking estrogen and blocking testosterone, it turns out that one of the side effects of that blockade is a real weakening of the bones and a stimulation of osteoclast activity. And so there’s been increasing recognition that the bone-weakening effects of some of our therapies – the growth factors and some of the anti-estrogens – are important to recognize, not only because we don’t want our patients to develop osteoporosis and fractures. We want to have the strongest skeletons that we can because we want our patients to have the best chance of resisting bone metastasis.

Host: How do such research findings affect your medical practice?

Weilbaecher: What I tell my patients is that in addition to what I as a physician can do in terms of getting them the best medicines and knowing all of the side effects, what I ask them to do is to exercise because one of the ways to keep your skeleton strong is by walking. When you do weight-bearing exercise such as walking, that can give a message to the bone to strengthen the bones. To make sure they have enough calcium intake. And increasingly, I think it’s important for patients to take vitamin D because vitamin D helps calcium get put into the bone.

Host: Dr. Weilbaecher, thank you for joining us.

Weilbaecher: It was my pleasure. Thank you.