OBJECTIVES: I. Determine the toxicity associated with repeated vaccination with recombinant vaccinia DF3/MUC1 vaccine (rV-DF3/MUC1) in patients with metastatic breast cancer. II. Determine the maximum tolerated dose of rV-DF3/MUC1, based on cellular and humoral immunity, in these patients. III. Determine whether vaccination with rV-DF3/MUC1 is associated with antitumor activity in these patients.