Experimental Medicine Seems to Help Treat Estrogen-Receptor-Positive, HER2-Negative, Advanced-Stage Breast Cancer

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An early study suggests that the experimental medicine PD 0332991, also called palbociclib, given in combination with Femara (chemical name: letrozole) offers more benefits in treating advanced-stage, estrogen-receptor-positive, HER2-negative breast cancer than Femara alone.

The study, “Results of a randomized phase 2 study of PD 0332991, a cyclindependent kinase 4/6 inhibitor, in combination with letrozole vs letrozole alone for first-line treatment of ER+/HER2-advanced breast cancer" was presented at the 2012 San Antonio Breast Cancer Symposium.

Palbociclib is a cyclin-dependent 4/6 kinase inhibitor. A kinase is a type of protein in the body that helps control cell division. PD 0332991 works by stopping cancer cells from dividing and growing.

Femara is an aromatase inhibitor, a type of hormonal therapy medicine. Femara works by stopping the production of estrogen in postmenopausal women. This means that less estrogen is available to stimulate the growth of hormone-receptor-positive breast cancer cells.

Both palbociclib and Femara are pills taken by mouth.

In this small, early study, 168 women diagnosed with advanced-stage, estrogen-receptor-positive, HER2-negative breast cancer were assigned to be treated with either Femara alone or Femara plus palbociclib:

  • 84 women got Femara plus palbociclib
  • 84 women got Femara alone

The women were about 63 years old and about 30% of them had had a breast cancer come back (recurrence) within a year after adjuvant treatment.

Doctors call treatments given after surgery for early-stage or advanced-stage cancer (but not metastatic cancer), such as hormonal therapy and radiation therapy, adjuvant treatments.

The Femara-palbociclib combination lengthened the time before the cancer grew:

  • women who got Femara and palbociclib lived for 26.1 months before the cancer grew
  • women who got only Femara lived for 7.5 months before the cancer grew

Palbociclib didn’t seem to cause any severe side effects. The most common side effect was low white blood cell count, which doctors call neutropenia. There are medicines that treat neutropenia by stimulating the immune system to make more white blood cells.

While these results are promising, they are early results. More research is needed so doctors know the best way to use palbociclib to treat breast cancer.

If you’re being treated for advanced-stage, estrogen-receptor-positive, HER2-negative breast cancer, you and your doctor may be considering a number of options, especially if the cancer has stopped responding to standard treatments. Treatment with an experimental regimen that includes palbociclib may be an option if you’re willing to participate in a clinical trial. Ask your doctor if there are any clinical trials that might be a good fit for you and your unique situation. Visit the Breastcancer.org Clinical Trials pages for more information.

And stay tuned to Breastcancer.org for the latest information on palbociclib and other new breast cancer treatments.

Editor’s Note: On Feb. 3, 2015, the U.S. Food and Drug Administration granted accelerated approval for using the targeted therapy Ibrance (chemical name: palbociclib) in combination with Femara (chemical name: letrozole) to treat advanced-stage, estrogen-receptor-positive, HER2-negative breast cancer that hadn’t been treated with hormonal therapy before in postmenopausal women.

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