I. To estimate the response rate and toxicity to low-dose IL-2 with intermediate-"pulse" dose interleukin 2 (IL-2) and trastuzumab in patients with uni-dimensional measurable metastatic breast cancer and human epidermal growth factor receptor 2 (HER2) positive (3+ overexpression by immunohistochemistry [IHC] method or positive by fluorescent in situ hybridization [FISH]) who either have had evidence of progressive disease while receiving a trastuzumab-containing regimen, or have had progressive disease within 12 months of receiving a trastuzumab-containing regimen.