This single-arm open-label study assessed the safety, feasibility, and efficacy of trastuzumab emtansine (T-DM1) after the completion of anthracycline-based adjuvant/neoadjuvant chemotherapy in patients with early HER2-positive breast cancer. Patients received T-DM1 3.6 mg/kg intravenously on Day 1 of each 3-week cycle, for up to 17 cycles.

Inclusion Criteria:

• Adult patients ≥ 18 years of age.
• Locally advanced, inflammatory, or early stage, unilateral, and histologically confirmed invasive breast cancer documented at a local laboratory (patients with inflammatory breast cancer must be able to have a core needle biopsy).
• Herceptin (HER)2-positive tumor, confirmed by central testing using immunohistochemistry (IHC) and in situ hybridization (ISH) methods.
• Willingness to receive anthracycline-based chemotherapy or have received doxorubicin/cyclophosphamide (AC) OR 5-fluorouracil (FU)/epirubicin/ cyclophosphamide (FEC) in a similar dose and schedule as described in the protocol as part of neoadjuvant or adjuvant treatment.
• For women of childbearing potential and men with partners of childbearing potential, agreement to use a highly effective, non-hormonal form of contraception or 2 effective forms of non-hormonal contraception by the patient and/or partner. Contraception use must continue for the duration of study treatment and for at least 6 months after the last dose of study treatment. Male patients should use condoms for the duration of the study. Specific country requirements will be followed.
• Negative results of serum pregnancy test for premenopausal women of reproductive capacity and for women < 12 months after menopause.
• Patients may enroll before or after AC/FEC chemotherapy has completed.
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
• Adequate hematologic, biochemistry, and cardiac assessments.

Exclusion Criteria:

• Stage IV breast cancer or bilateral breast cancer.
• Pregnant or breastfeeding women.
• History of other malignancy within the previous 5 years, except contralateral breast cancer and ductal carcinoma in situ (DCIS)/lobular carcinoma in situ (LCIS), appropriately treated carcinoma in situ of the cervix, non-melanoma skin carcinoma, Stage I uterine cancer, or other cancers with outcome similar to those mentioned above.
• Radiation therapy, immunotherapy, or biotherapy within 5 years before study enrollment; non-cardiotoxic chemotherapy for malignancy treated > 5 years before study enrollment is allowed. Patients receiving AC/FEC in a similar fashion to the study treatment prescribed for adjuvant or neoadjuvant treatment of breast cancer will be allowed to enroll in the study after the completion of their AC/FEC. No other prior history of cardiotoxic chemotherapy is allowed.
• Active cardiac history.
• Current chronic daily treatment with oral corticosteroids or equivalent.
• Patients with severe dyspnea at rest or requiring supplementary oxygen therapy.
• Active, unresolved infections at screening.
• Human immunodeficiency virus (HIV), hepatitis B virus (HBV), or hepatitis C virus (HCV) infection.
• Major surgery within 4 weeks before enrollment that is unrelated to the breast cancer.
• Patients for whom concomitant radiotherapy + T-DM1 may be contraindicated yet radiation therapy is planned.
• Known hypersensitivity to any of the study drugs or derivatives, including murine proteins.
• Grade ≥ 2 peripheral neuropathy at Baseline.