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Medicine Combination Slows Metastatic HER2 Positive Breast Cancer

A study showing pertuzumab improves progression-free survival

January 26, 2012

Written By Michael J. Formica, MS, MA, EdM
Reviewed By Heather L. McArthur, MD, MPH

Results from the CLEOPATRA clinical trial presented at the San Antonio Breast Cancer Symposium showed combining trastuzumab (Herceptin) and the experimental medicine pertuzumab with chemotherapy may offer a new treatment option for women with metastatic HER2 positive breast cancer.

The study, published online in the New England Journal of Medicine, showed the two medicines combined with the chemotherapy medicine docetaxel (Taxotere) led to a six-month improvement in progression-free survival compared to trastuzumab and docetaxel alone. Progression-free survival is the length of time after treatment begins that breast cancer does not grow.

Background and Reason for the Study

HER2 positive breast cancers have too much HER2 protein. The HER2 protein plays an important role in normal cell growth, but too much prompts cells to grow more rapidly than normal. Blocking cells’ ability to grow can slow or stop the spread of cancer.

Both trastuzumab and pertuzumab block cancer cells’ ability to receive growth signals, but do so in different ways. Research suggests the two medicines could work together to improve trastuzumab’s ability to weaken or destroy cancer cells.

Researchers have been considering how these two medicines work together to treat HER2 positive breast cancer. The trastuzumab and pertuzumab combination is sometimes referred to as dual HER2 antibody therapy.

Structure of the Study

Researchers randomly assigned 808 previously untreated women with metastatic HER2-positive breast cancer to one of two equal groups. One group received the study treatment of trastuzumab, docetaxel and pertuzumab. The other group received the standard treatment of trastuzumab, docetaxel and a placebo, or inactive substance.

The purpose of the study was to measure differences in progression-free survival for the two groups. Researchers also looked at length of overall survival, the time from start of treatment until death from any cause, as well as side effects.

Results of the Study

The difference in progression-free survival for the group treated with trastuzumab, docetaxel and pertuzumab and those treated with trastuzumab and docetaxel alone was statistically significant, or unlikely to have happened by chance.

Half of the group that received pertuzumab had no cancer growth for 18.5 months, while the other half had growth within a shorter period. In the second group, half had no cancer growth for 12.4 months, and the other half of this group had growth sooner.

Common serious side effects in both groups were neutropenia, or low white blood cell count, and diarrhea. Including pertuzumab did not increase risk of heart problems, which can sometimes be a side effect of trastuzumab.

These early results suggest positive overall survival in the group that included pertuzumab. Researchers will continue to follow the participants’ progress longer to see if overall survival is improved. Final results for overall survival are expected in 2013.

What This Means for You

If you are being treated for metastatic HER2 positive breast cancer, you and your care team are likely considering several treatment options. Clinical trials may give you more options, including treatment with experimental medicines like pertuzumab. If you feel comfortable participating in a clinical trial, talk with your care team. You can also read LBBC’s Guide to Understanding Breast Cancer Treatment Research Studies for more information.

Learn more about this study in the abstract and in the published paper.

1Baselga, J., et. al. A phase III, randomized, double-blind, placebo-controlled registration trial to evaluate the efficacy and safety of pertuzumab + trastuzumab + docetaxel vs. placebo + trastuzumab + docetaxel in patients with previously untreated HER2-positive metastatic breast cancer (CLEOPATRA). Presented at the 34th Annual San Antonio Breast Cancer Symposium, Abstract S5-5

2Baselga, J., et. al. Pertuzumab plus Trastuzumab plus Docetaxel for Metastatic Breast Cancer. The New England Journal of Medicine January 2012 366:109-119