T-DM1 vs Paclitaxel/Trastuzumab for Breast (ATEMPT Trial)

If a participant agrees to participate in this study she will be asked to undergo some screening tests or procedures to confirm that she is eligible. Many of these tests and procedures are likely to be part of regular cancer care and may be done even if turns out that she does not take part in this research study. If she has had some of these tests or procedures recently, they may or may not have to be repeated. These tests and procedures will include: a medical history, performance status, assessment of your tumor, blood tests, cardiac tests, pregnancy test and a collection of tumor tissue. If these tests show that she is eligible to participate in the research study, she will begin the study treatment. If she does not meet the eligibility criteria, she will not be able to participate in this research study.

Because no one knows which of the study options is best, the participant will be "randomized" into one of the study groups after she has had her breast surgery: Group 1 or Group 2. Randomization means that she is put into a group by chance. Neither the participant nor the research doctor will choose what group she will be in. The participant will have a one in three chance of being placed in any group. Approximately 375 study participants will receive the study drug, while 125 study participants will receive the standard therapy of trastuzumab and paclitaxel.

Group 1 participants will receive the study drug T-DM1 every three weeks by IV (intravenous injection) for 17 treatments (total of 51 weeks).

Group 2 participants will receive the FDA-approved drugs Paclitaxel and Trastuzumab once per week by IV for 12 weeks. Then beginning week 13, participants will receive Trastuzumab only by IV injection every three weeks for the next 13 treatments.

During all cycles the participant will have a physical exam and tumor assessment.

The investigators would like to keep track of the participant's medical condition for the next five years after the final dose of study drug. The investigators would like to do this by regular visits every 6 months for 3 years after completion of study treatment, and then once a year for the next two years. The investigators may ask for additional follow-up by phone after completion of these visits.

Participants who undergo lumpectomy (breast conserving surgery) need to receive breast radiation therapy to participate in this study. Participants who have undergone a mastectomy may receive chest wall and lymph node radiation (as determined by discussion with their physician). Radiation Therapy will begin after the conclusion of all study paclitaxel doses, and after 12 weeks fo the study drug T-DM1.