For Some Breast Cancers, New Drug May Be Treatment Option

Adapted from the NCI Cancer Bulletin.

Results from an international clinical trial suggest that women with metastatic HER2-positive breast cancer that is no longer responding to the targeted therapy trastuzumab (Herceptin®) may soon have a new treatment option.

Women who received the investigational drug trastuzumab emtansine (T-DM1) lived more than 3 months longer without their tumors progressing than women who received the chemotherapy drug capecitabine (Xeloda®) and the targeted drug lapatinib (Tykerb®). With one exception, T-DM1 also had far fewer serious side effects than the capecitabine-lapatinib combination, the trial’s leaders reported at the 2012 American Society of Clinical Oncology annual meeting.

“T-DM1 should offer an important therapeutic option in the treatment of HER2-positive breast cancer,” said the study’s lead investigator, Kimberly Blackwell, M.D., of the Duke Cancer Institute at Duke University.

The drug’s manufacturer, Genentech, stated it will seek approval from the Food and Drug Administration this year for use of T-DM1 in women with metastatic breast cancer.

T-DM1 is an antibody-drug conjugate composed of the monoclonal antibody trastuzumab, which targets the HER2 receptor on breast cancer cells, chemically linked to the chemotherapy drug DM1.

The median progression-free survival in women treated with T-DM1 was 9.6 months, compared with 6.4 months in women treated with capecitabine and lapatinib, Dr. Blackwell reported. The results were based on an interim analysis of the trial’s data. Overall survival was similar in the two treatment groups, but at the time of the analysis there was a statistical trend toward improved overall survival, with more than 65 percent of patients in the T-DM1 treatment group still alive after 2 years compared with more than 47 percent of patients in the capecitabine-lapatinib control group.

Although more women taking T-DM1 had a potentially dangerous drop in platelet levels (thrombocytopenia), other side effects such as vomiting, diarrhea, and hand-foot syndrome were much more likely in women in the control group. The thrombocytopenia was effectively managed with dose reductions, Dr. Blackwell noted, and more women in the control group had to have their dose reduced because of side effects.

“T-DM1 really works in this population,” said Louis Weiner, M.D., of the Georgetown Lombardi Comprehensive Cancer Center during the plenary session. Additional research is needed to better understand how best to use it in combination with other available treatments, Dr. Weiner continued.