Gemcitabine, Trastuzumab, and Pertuzumab in the Treatment of Metastatic HER2-Positive Breast Cancer After Prior Trastuzumab/Pertuzumab, or Pertuzumab Based Therapy

Inclusion Criteria:

- Age ≥ to 18

- Stage IV HER2 (+) breast cancer

- Histologically documented HER2 (+) breast cancer as defined as IHC 3+ or FISH
amplification of ≥ 2.0 of primary or metastatic site; results from the local lab are
acceptable.

- lECOG performance status 0 -1

- Prior treatment with trastuzumab + pertuzumab (HP)-based therapy or pertuzumab-based
in the neoadjuvantadjuvant, unresectable, locally advanced, or metastatic setting.

- ≤ 3 prior chemotherapies in the metastatic setting. Prior anthracycline, taxane,
gemcitabine, and anti-HER2 agents (i.e. trastuzumab, pertuzumab, lapatinib, neratinib,
TDM-1, etc.) are allowed. If patients received prior gemcitabine, it could not have
been combined with pertuzumab. Patients should have progression of disease on current
therapy.

- Measurable or non-measurable disease.

- LVEF ≥ 50%

- Hematologic parameters: white blood cell (WBC) count of ≥ 3000/ul, absolute neutrophil
count (ANC) ≥ 1000/ul, platelets ≥ 100,000/ul, hemoglobin ≥10.0 g/dl

- Non-hematologic parameters: bilirubin ≤ 1.5 mg/dl, AST/ALT≤ 2.5 x upper limit of
normal (ULN), alkaline phosphatase ≤ 5 x ULN.

- Creatinine ≤ 1.5 mg/dl

- Patients with "treated and stable" brain lesions of a duration of ≥ 2 months may be
enrolled.

Exclusion Criteria:

- History of prior unstable angina, myocardial infarction, CHF, uncontrolled ventricular
arrhythmias within 12 months

- History of prior ≥ G 3 hypersensitivity (HSR) or any toxicity to trastuzumab or
pertuzumab that warranted permanent cessation of this agent

- History of hepatitis B or C

- Pregnant patients