Prolia (chemical name: denosumab) is a targeted therapy used to treat bone loss in women taking aromatase inhibitors as part of their breast cancer treatment. Prolia is given as an injection under the skin every 6 months at a dose of 60 mg.
A study has found that Prolia reduced the risk of breaking a bone by 50% in postmenopausal women diagnosed with early-stage, hormone-receptor-positive breast cancer who were taking an aromatase inhibitor.
The research was presented on June 1, 2015 at the American Society of Clinical Oncology annual meeting. Read the abstract of “Adjuvant denosumab in breast cancer: Results from 3,425 postmenopausal patients of the ABCSG-18 trial.”
Aromatase inhibitors are hormonal therapy medicines often used to treat postmenopausal women diagnosed with hormone-receptor-positive breast cancer after surgery to reduce the risk of the cancer coming back (recurrence).
The aromatase inhibitors are:
- Arimidex (chemical name: anastrozole)
- Aromasin (chemical name: exemestane)
- Femara (chemical name: letrozole)
Hormonal therapy given after surgery is called adjuvant hormonal therapy.
Hot flashes, night sweats, and joint pain are common side effects of aromatase inhibitors. These medicines also can weaken bones over time and increase chances of breaking a bone. So it makes sense to use medicine and other steps to strengthen bones while taking an aromatase inhibitor.
Prolia also is used to treat postmenopausal women diagnosed with osteoporosis at high risk of breaking a bone or who haven’t gotten any benefits from other osteoporosis medicines.
Denosumab is also branded as Xgeva, which is approved to reduce the risk of bone complications (such as fracture) and bone pain caused by advanced-stage cancers, including breast cancer, which have spread to bone. Xgeva is given as an injection under the skin every 4 weeks at a dose of 120 mg.
Denosumab is a targeted therapy, which means it targets specific characteristics of cells. Some targeted therapies, including denosumab, are antibodies that work like the antibodies made naturally by the immune system. Denosumab targets a protein called RANK ligand (RANKL). RANKL affects the activity of certain bone cells called osteoclasts. Osteoclasts help with normal bone breakdown activity to regulate calcium levels. Denosumab blocks RANKL activity and limits osteoclast activity. So denosumab treats osteoporosis by restoring a healthier balance of bone building and bone breakdown. In women who have been diagnosed with breast cancer that has spread to bone, osteoclasts tend to be overactive. These overactive osteoclasts can cause bone pain and bone destruction. By blocking the RANKL protein, denosumab lowers the activity level of the osteoclasts in women whose cancer has spread to bone, reducing their risk of pain and other bone complications.
In this study, the researchers randomly assigned 3,425 postmenopausal women diagnosed with early-stage, hormone-receptor-positive breast cancer who were taking an aromatase inhibitor to one of two bone treatments:
- Prolia injection every 6 months at a dose of 60 mg
- a placebo injection every 6 months of a substance that looked just like Prolia
They wanted to see if Prolia helped reduce the risk of breaking a bone and are also continuing to follow the women to see if Prolia helps reduce recurrence risk.
The results showed that women who got Prolia had about half the number of broken bones as women who got the placebo:
- 92 women treated with Prolia broke a bone
- 176 women treated with the placebo broke a bone
This difference was statistically significant, which means that it was likely due to the difference in treatment and not just because of chance.
Women who got Prolia also had higher bone density as measured in the spine, hip, and neck at 1, 2, and 3 years of treatment compared to bone density levels before they were treated with Prolia. Women who got the placebo had their bone density drop.
Possible side effects of Prolia include back, arm, and leg pain; high cholesterol levels; and urinary infections. More serious but much less common side effects include low blood calcium levels, rashes, and severe infections. In rare cases Prolia can cause breakdown of the jaw bone (called osteonecrosis of the jaw).
In this study, Prolia caused no severe side effects and none of the women developed osteonecrosis of the jaw.
If you’re a postmenopausal woman who’s been diagnosed with early-stage, hormone-receptor-positive breast cancer and will be taking an aromatase inhibitor after surgery, you might want to talk to your doctor about this study. Ask your doctor what steps you can take to maintain or restore your bone health and whether a medicine such as Prolia might make sense for your unique situation.
Visit the Bone Health section of Breastcancer.org to learn more about the steps you can take to keep your bones strong during and after breast cancer treatment. In this section, you can learn about diet and lifestyle changes for maintaining bone health, as well as bone strengthening medicines.