Low-dose recombinant interleukin-2 and low-dose cyclophosphamide in metastatic breast cancer.

We undertook a preliminary study to examine the response rate of recombinant interleukin-2 (rIL-2) in patients with advanced measurable breast cancer, in a phase II clinical trial. The regimen we utilized was designed to allow outpatient administration. A treatment cycle consisted of low-dose cyclophosphamide (350 mg/m2) given on day -3 followed by the bolus administration of rIL-2 (3.6 x 10(6) Cetus units/m2) on days 1-5, and 8-12. Toxicity was significant but acceptable. One partial remission was seen in 13 evaluable patients. In 2 additional patients clear evidence of an antitumor response was observed. The study was terminated prematurely owing to a shortage of rIL-2. Additional evaluation of rIL-2 in breast cancer appears warranted.