OBJECTIVES: I. Determine the toxic effect profile and maximum tolerated dose of interleukin-12 (rhIL-12) in women with advanced breast cancer who have undergone high dose chemotherapy with stem cell rescue. II. Determine the effect of rhIL-12 on cellular and humoral immune systems following high dose chemotherapy. III. Explore the effect on treatment failure of rhIL-12 after high dose chemotherapy with stem cell rescue.