Biomarker Analysis Identified Women Most Likely to Benefit From T-DM1

• Patients with the highest tumor HER2 levels benefited most.
• The EMILIA phase III clinical trial led to FDA approval of T-DM1.
• Presence of tumor PIK3CA mutations did not diminish treatment response.

WASHINGTON, D.C. — For women with metastatic, HER2-positive breast cancer, the amount of HER2 on their tumor might determine how much they benefit from a drug called trastuzumab emtansine (T-DM1), according to data from a subanalysis of the phase III clinical trial that led the U.S. Food and Drug Administration to approve the drug on Feb. 22, 2013. These findings were presented by José Baselga, M.D., Ph.D., physician-in-chief at Memorial Sloan-Kettering Cancer Center in New York, N.Y., at the AACR Annual Meeting 2013, held in Washington, D.C., April 6-10.

“EMILIA was a landmark phase III clinical trial,” said Baselga. “It showed that T-DM1 prolonged progression-free and overall survival for patients with HER2-positive metastatic breast cancer that had been previously treated with trastuzumab and a taxane chemotherapy compared with lapatinib plus capecitabine. Also, it provided proof-of-concept that a new class of drugs called antibody-drug conjugates can benefit patients.”

Antibody-drug conjugates consist of an antibody attached to a toxic chemotherapy, according to Baselga. In the case of T-DM1, the antibody is trastuzumab and the toxic chemotherapy is emtansine. Trastuzumab recognizes the protein HER2, which is found at high levels in HER2-positive breast cancers, and targets the emtansine to the HER2-positive cancer cells, which are killed by the toxic chemotherapy.

In this subanalysis, Baselga and colleagues analyzed tissue samples from patients enrolled in EMILIA to examine whether tumor levels of HER2, as assessed by the amount of HER2 messenger ribonucleic acid (mRNA), affected treatment response. Patients with tumor samples expressing greater than the median amount of tumor HER2 mRNA were considered to have high levels of HER2. Those with tumor samples expressing the median amount of tumor HER2 mRNA or less were considered to have low levels of HER2.

“Even though everyone enrolled in the clinical trial had breast cancer expressing elevated levels of HER2, we know that each person’s tumor has different molecular features,” said Baselga. “Even the degree to which HER2 expression is elevated differs from patient to patient.”

Consistent with the prior analysis, he and his colleagues found that all patients treated with T-DM1 had significantly longer progression-free and overall survival compared with those treated with lapatinib and capecitabine (9.6 months progression-free survival versus 6.4 months; and 30.9 months for overall survival versus 25.1 months).

Patients with tumors expressing higher levels of HER2 derived greater benefit from treatment with T-DM1 compared with patients with tumors expressing lower levels of HER2: Overall survival was 34.1 months for those with high levels of HER2 versus 26.5 months. For patients with tumors expressing higher levels of HER2, those receiving T-DM1 had a 47 percent decreased risk for death compared with those receiving lapatinib and capecitabine.

The researchers also investigated whether tumor mutations in the PIK3CA gene affected treatment response. According to Baselga, patients with PIK3CA-mutated, HER2-positive breast cancer normally do not respond as well to treatment with conventional HER2-targeted therapies such as trastuzumab compared with patients without PIK3CA mutations in their tumors.

However, for patients treated with T-DM1, PIK3CA mutation status did not significantly decrease progression-free survival.

“Our findings are an important step toward identifying the best therapy for individual patients with HER2-positive breast cancer,” said Baselga. “HER2-positive breast cancer is not a uniform disease; each patient is different. These data help us as we look to identify a panel of molecular features that we can use to make informed treatment decisions.”

Kadcyla (ado-trastuzumab emtansine or T-DM1) is a trademark of Genentech, a member of the Roche Group.

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About the American Association for Cancer Research
Founded in 1907, the American Association for Cancer Research (AACR) is the world’s first and largest professional organization dedicated to advancing cancer research and its mission to prevent and cure cancer. AACR membership includes more than 34,000 laboratory, translational and clinical researchers; population scientists; other health care professionals; and cancer advocates residing in more than 90 countries. The AACR marshals the full spectrum of expertise of the cancer community to accelerate progress in the prevention, biology, diagnosis and treatment of cancer by annually convening more than 20 conferences and educational workshops, the largest of which is the AACR Annual Meeting with more than 17,000 attendees. In addition, the AACR publishes eight peer-reviewed scientific journals and a magazine for cancer survivors, patients and their caregivers. The AACR funds meritorious research directly as well as in cooperation with numerous cancer organizations. As the scientific partner of Stand Up To Cancer, the AACR provides expert peer review, grants administration and scientific oversight of team science and individual grants in cancer research that have the potential for near-term patient benefit. The AACR actively communicates with legislators and policymakers about the value of cancer research and related biomedical science in saving lives from cancer. For more information about the AACR, visit www.AACR.org.

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