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This phase III trial studies how well trastuzumab emtansine (T-DM1) and tucatinib work in preventing breast cancer from coming back (relapsing) in patients with high risk, HER2 positive breast cancer. T-DM1 is a monoclonal antibody, called trastuzumab, linked to a chemotherapy drug, called DM1. Trastuzumab is a form of targeted therapy because it attaches to specific molecules (receptors) on the surface of cancer cells, known as HER2 receptors, and delivers DM1 to kill them. Tucatinib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Giving T-DM1 and tucatinib may work better in preventing breast cancer from relapsing in patients with HER2 positive breast cancer compared to T-DM1 alone.
PRIMARY OBJECTIVE:
I. To determine if the invasive disease-free survival (iDFS) with T-DM1 and tucatinib is superior to the iDFS in the control arm (T-DM1 + placebo) when administered to high risk patients with HER2-positive breast cancer and residual disease after neoadjuvant HER2-directed therapy.
SECONDARY OBJECTIVES:
I. To evaluate whether treatment with tucatinib plus T-DM1 compared to treatment with T-DM1 alone (T-DM1 plus placebo) improves the following:
Ia. Breast cancer free survival (BCFS). Ib. Distant recurrence-free survival (DRFS). Ic. Brain metastases-free survival (BMFS). Id. Overall survival (OS). II. To evaluate whether treatment with tucatinib plus T-DM1 compared to treatment with T-DM1 alone (T-DM1 plus placebo) reduces the incidence of brain metastases.
OUTLINE: Patients are randomized to 1 of 2 arms.
ARM I: Patients receive T-DM1 intravenously (IV) over 30-90 minutes on day 1 and placebo orally (PO) twice daily (BID) on days 1-21. Treatment repeats every 21 days for up to 14 cycles in the absence of disease progression or unacceptable toxicity.
ARM II: Patients receive T-DM1 IV over 30-90 minutes on day 1 and tucatinib PO BID on days 1-21. Treatment repeats every 21 days for up to 14 cycles in the absence of disease progression or unacceptable toxicity.
After completion of study treatment, patients are followed up at 30 days, then every 6 months for 10 years.
