A Study of Trastuzumab Emtansine Versus Trastuzumab as Adjuvant Therapy in Patients With HER2-Positive Breast Cancer Who Have Residual Tumor in the Breast or Axillary Lymph Nodes Following Preoperative Therapy (KATHERINE)

Inclusion Criteria:

1. Adult patient, >/= 18 years of age
2. HER2-positive breast cancer
3. Histologically confirmed invasive breast carcinoma
4. Clinical stage T1-4/N0-3/M0 at presentation (patients with T1a/bN0 tumors will not be eligible)
5. Completion of preoperative systemic chemotherapy and HER2-directed treatment consisting of at least 6 cycles of chemotherapy with a total duration of at least 16 weeks, including at least 9 weeks of trastuzumab and at least 9 weeks of taxane-based therapy
6. Adequate excision: surgical removal of all clinically evident disease in the breast and lymph nodes as specified in protocol
7. Pathological evidence of residual invasive carcinoma in the breast or axillary lymph nodes following completion of preoperative therapy
8. An interval of no more than 12 weeks between the date of surgery and the date of randomization
9. Known hormone-receptor status
10. Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1
11. Adequate hematologic, renal and liver function
12. Screening Left ventricular ejection fraction (LVEF) >/= 50% on echocardiogram (ECHO) or multiple-gated acquisition (MUGA) after receiving neoadjuvant chemotherapy and no decrease in LVEF by more than 15% absolute points from the pre-chemotherapy LVEF. Or, if pre-chemotherapy LVEF was not assessed, the screening LVEF must be >/= 55% after completion of neoadjuvant chemotherapy.
13. For women who are not postmenopausal or surgically sterile: agreement to remain abstinent or use single or combined contraceptive methods that result in a failure rate of < 1% per year during the treatment period and for at least 7 months after the last dose of study drug
14. Documentation of hepatitis B virus and hepatitis C virus serology is required

Exclusion Criteria:

1. Stage IV (metastatic) breast cancer
2. History of any prior (ipsi- or contralateral breast cancer except lobular carcinoma in situ
3. Evidence of clinically evident gross residual or recurrent disease following preoperative therapy and surgery
4. Progressive disease during preoperative systemic therapy
5. Treatment with any anti-cancer investigational drug within 28 days prior to commencing study treatment
6. History of other malignancy within the last 5 years except for appropriately treated carcinoma in situ of the cervix, non-melanoma skin carcinoma, Stage I uterine cancer, or other non-breast malignancies with a similar outcome to those mentioned above
7. Patients for whom radiotherapy would be recommended for breast cancer treatment but for whom it is contraindicated because of medical reasons
8. Current NCI CTCAE (Version 4.0) Grade >/= 2 peripheral neuropathy
9. History of exposure to the following cumulative doses of anthracyclines: Doxorubicin > 240 mg/m2; Epirubicin or Liposomal Doxorubicin-Hydrochloride (Myocet®) > 480 mg/m2; For other anthracyclines, exposure equivalent to doxorubicin > 240 mg/m2
10. Cardiopulmonary dysfunction as defined by protocol
11. Prior treatment with trastuzumab emtansine
12. Current severe, uncontrolled systemic disease
13. Pregnant or lactating women
14. Any known active liver disease, e.g. due to HBV, HCV, autoimmune hepatic disorders, or sclerosing cholangitis
15. Concurrent serious uncontrolled infections requiring treatment or known infection with HIV
16. History of intolerance, including Grade 3 to 4 infusion reaction or hypersensitivity to trastuzumab or murine proteins or any components of the product