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)

- HER2-positive tumor, confirmed by central testing using IHC and ISH methods

- Willingness to receive anthracycline-based chemotherapy or have received
doxorubicin/cyclophosphamide (AC) OR 5-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 two
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

- HIV, HBV or 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