Inclusion Criteria:

* Histologically confirmed invasive carcinoma of the breast
* Tumors must be less than or equal to 3cm in greatest dimension
* Must have node-negative breast cancer according to teh AJCC 7th edition
* ER/PR determination is required. ER- and PR-assays should be performed by immunohistochemical methods
* HER-2 positive: IHC 3+ or FISH \>2
* Bilateral breast cancers that individually meet eligibility criteria are allowed
* Patients should have tumor tissue available, and a tissue block of sufficient size to make 15 slides must be sent to DFCI for testing
* Less than or equal to 84 days from mastectomy or from axillary dissection or sentinel node biopsy if the patient's most extensive breast surgery was a breast-sparing procedure
* All tumor should be removed by either a modified radical mastectomy or a segmental mastectomy (lumpectomy), with either a sentinel node biopsy or axillary dissection
* 18 years of age or older
* ECOG Performance Status of 0 or 1
* Adequate bone marrow function, hepatic function, and renal function as outlined in protocol
* Left ventricular ejection fraction of greater than or equal to 50%
* Willingness to discontinue any hormonal agent prior to registration and while on study
* Willingness to discontinue sex hormonal therapy, e.g. birth control pills, prior to registration and while on study
* Patients with a history of ipsilateral DCIS are eligible if they were treated with wide-excision alone, without radiation therapy
* Patients undergoing breast conservation therapy must not have any contraindications to radiation therapy

Exclusion Criteria:

* Pregnant or nursing women
* Locally advanced tumors at diagnosis, including tumors fixed to the chest wall, peau d'orange, skin ulcerations/nodules, or clinical inflammatory changes
* History of prior chemotherapy in past 5 years
* History of prior trastuzumab therapy
* Active, unresolved infection
* Prior history of any other malignancy in the past 5 years, except for early stage tumors of the skin or cervix treated with curative intent
* Sensitivity to benzyl alcohol
* Grade 2 or greater neuropathy per NCI's CTCAv3.0. (Exception: Any chronic neurologic disorder will be looked at on a case-by-case basis by the study chair).
* Active cardiac disease as outlined in protocol.