OUTLINE: This is a randomized, multicenter study. Patients are stratified according to number of prior therapies for metastatic breast cancer (1 vs 2). Patients are randomized to one of two treatment arms. (Arm I closed 12/22/99) Arm I: Patients receive ISIS 5132 IV continuously over 21 days. (closed 12/22/99) Arm II: Patients receive ISIS 3521 IV continuously over 21 days. Treatment repeats every 4 weeks in the absence of disease progression or unacceptable toxicity. After every 2 courses, patients are evaluated for response. Patients are followed every 3 months for the first 2 years, every 6 months the next 3 years, then annually thereafter.