Researchers conducted an international phase 3, double-blind, randomized trial, known as CLEOPATRA (CLinical Evaluation Of Pertuzumab And TRAstuzumab), in which they randomly assigned 808 patients to receive trastuzumab and docetaxel chemotherapy with pertuzumab or placebo. Progression-free survival (PFS) was 18.5 months for patients who received pertuzumab compared with 12.4 months for patients who received placebo - a 38 percent reduction in risk for progression.
The findings, reported at the 2011 CTRC-AACR San Antonio Breast Cancer Symposium, held Dec. 6-10, 2011, represent a significant advance in the treatment of this advanced breast cancer, said senior researcher José Baselga, M.D., Ph.D., professor in the department of medicine at Harvard Medical School, associate director of the Massachusetts General Hospital Cancer Center and chief of hematology/oncology at Massachusetts General Hospital.
"This is huge. It is very uncommon to have a clinical trial show this level of improvement in PFS," said Baselga. "Most metastatic patients with HER2-positive breast cancer eventually stop responding to trastuzumab, so the fact that we now have an agent that can be added to current treatment to delay progression is very exciting. With the advent of trastuzumab and now pertuzumab, we have come a very long way in treating a type of breast cancer that once had a very poor prognosis."
Drugs -- anastrozole (Arimidex) and fulvestrant (Faslodex) -- are currently used to treat breast cancer but they have typically been administered separately, not together.
The results of the randomized, controlled SWOG trial showed that the two anti-estrogen drugs given together extended the median survival time by more than six months compared to standard treatment with anastrozole only.
The study began in 2004 and included 707 postmenopausal women with metastatic hormone receptor-positive breast cancer.
All the women took a daily oral dose of anastrozole, which works by reducing production of tumor-promoting estrogen.
About half of the women also got a 250 milligram injection of fulvestrant every 28 days. Fulvestrant works by interfering with the receptors that allow estrogen to signal cells to grow and reproduce.
Lead study coordinator Rita Mehta of the University of California, Irvine, Medical Center said the two drugs together showed an impressive impact on a subtype of breast cancer that accounts for more than half of all cases.
"If we take away estrogen and the estrogen receptor, the two together should be better than just doing one at a time," Mehta said.
"These patients have not had a new treatment that gave them an overall survival benefit in more than a decade."
Women in the trial who received just anastrozole survived a median of 41.3 months. Women who received the two in combination survived a median of 47.7 months.
Researchers said side effects were generally similar in both groups, though the most severe side effects, including one stroke and two pulmonary embolisms, were seen in the combination group.
"This most likely will change the standard of care for how we treat these patients," said study co-author Kathy Albain of Loyola University Medical Center.
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