Adding Aromatase Inhibitor to Perjeta and Herceptin Offers Benefits for Advanced-Stage Disease in Early Study

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The standard of care for people diagnosed with locally advanced or metastatic hormone-receptor-positive, HER2-positive breast cancer is a combination of the anti-HER2 targeted therapies Perjeta (chemical name: pertuzumab) and Herceptin (chemical name: trastuzumab) plus chemotherapy, usually a taxane, such as Taxol (chemical name: paclitaxel) or Taxotere (chemical name: docetaxel).

Locally advanced cancer is breast cancer that has spread to tissue near the breast, but not to parts of the body away from the breast. Metastatic breast cancer is cancer that has spread to parts of the body away from the breast, such as the bones or liver.

Still, some cancers become resistant to this treatment. Earlier research suggests that interactions between the HER2 receptor communication pathways and the estrogen receptor communication pathways in the cancer could be contributing to this treatment resistance.

So researchers wanted to see if adding an aromatase inhibitor to the targeted therapies instead of chemotherapy would help improve progression-free survival in women diagnosed with locally advanced or metastatic hormone-receptor-positive, HER2-positive breast cancer. Also, compared to the side effects of chemotherapy, the side effects of aromatase inhibitors are considered less toxic.

Progression-free survival is how long a woman lives without the cancer growing.

Results from an early study are promising: the combination of Perjeta, Herceptin, and an aromatase inhibitor led to longer progression-free survival than only Herceptin and an aromatase inhibitor.

The study was presented on Dec. 8, 2016 at the 2016 San Antonio Breast Cancer Symposium. Read the abstract of “Primary analysis of PERTAIN: A randomized, two-arm, open-label, multicenter phase II trial assessing the efficacy and safety of pertuzumab given in combination with trastuzumab plus an aromatase inhibitor in first-line patients with HER2-positive and hormone receptor-positive metastatic or locally advanced breast cancer.”

The phase II study, called PERTAIN, included 258 postmenopausal women diagnosed with HER2-positive, hormone-receptor-positive locally advanced or metastatic breast cancer. The cancer had not been treated with chemotherapy.

Phase II studies look at the effectiveness of a new treatment or combination of treatments. They are usually small, involving between 25 to 100 people. If a phase II study has good results, the new treatment will likely go on to a large phase III study.

The women in the PERTAIN study were randomly assigned to one of two treatments:

  • Perjeta, Herceptin, and an aromatase inhibitor -- either Arimidex (chemical name: anastrozole) or Femara (chemical name: letrozole)
  • Herceptin and an aromatase inhibitor -- either Arimidex (chemical name: anastrozole) or Femara (chemical name: letrozole)

Progression-free survival was:

  • 18.9 months for women treated with Perjeta, Herceptin, and an aromatase inhibitor
  • 15.8 months for women treated with Herceptin and an aromatase inhibitor

The three-drug combination also had a better response rate:

  • 63.3% of women treated with Perjeta, Herceptin, and an aromatase inhibitor had some response to the treatment
  • 55.7% of women treated with Herceptin and an aromatase inhibitor had some response to the treatment

Like most cancer treatments, Perjeta, Herceptin, and aromatase inhibitors can cause side effects, some of them serious.

About 50% of women treated with Perjeta, Herceptin, and an aromatase inhibitor had a severe side effect compared to about 40% of the women treated with Herceptin and an aromatase inhibitor. The most common side effects were diarrhea, hair loss, and nausea.

The researchers pointed out that the study isn’t a head-to-head comparison of Perjeta, Herceptin, and an aromatase inhibitor with Perjeta, Herceptin, and chemotherapy, but should make doctors more comfortable using an aromatase inhibitor with the two anti-HER2 targeted therapy medicines.

“The combination of pertuzumab, trastuzumab, and an aromatase inhibitor is effective and well-tolerated and may offer a novel treatment option for patients with HER2-positive, hormone-receptor-positive locally advanced or metastatic breast cancer,” said Mothaffar Rimawi, M.D., associate professor and medical director at the Lester and Sue Smith Breast Center at the Baylor College of Medicine, who was one of the study’s authors.

While these results are very promising, more research is needed before Perjeta, Herceptin, and an aromatase inhibitor becomes the standard of care for locally advanced or metastatic HER2-positive, hormone-receptor-positive breast cancer. A phase III trial on using Perjeta, Herceptin, and an aromatase inhibitor has been started in Germany.

If you’ve been diagnosed with locally advanced or metastatic HER2-positive, hormone-receptor-positive disease, you and your doctor are likely considering a number of treatments. You may want to ask your doctor about this study and whether the combination of Perjeta, Herceptin, and an aromatase inhibitor would be a good fit for your unique situation.

And stay tuned to Breastcancer.org for the latest information on new treatment combinations for locally advanced or metastatic disease.


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