DISEASE CHARACTERISTICS: Histologically proven metastatic adenocarcinoma of the breast Tumor tissue positive for staining with DF3 (CA27-29) and/or DF3-P OR Elevated serum CA15-3 (CA27-29) May have received no prior treatment or any number of prior regimens for metastatic disease Hormone receptor status: Not specified

PATIENT CHARACTERISTICS: Age: 18 and over Menopausal status: Not specified Performance status: ECOG 0 or 1 Life expectancy: Not specified Hematopoietic: WBC greater than 2,000/mm3 Platelet count greater than 100,000/mm3 Hepatic: Bilirubin less than 2.0 mg/dL SGPT less than 4 times upper limit of normal Renal: Creatinine less than 2.0 mg/dL Immunologic: At least normal delayed type hypersensitivity At least normal CD4:CD8 ratio (greater than 1) At least normal lymphocyte proliferation to concanavalin A At least normal immunoglobulin levels No evidence of altered immune responsiveness or autoimmune syndromes (scleroderma, systemic lupus erythematosus, etc.) If no antivaccinia antibodies, then must have physician certification of prior vaccinia immunization OR patient recollection and appropriate vaccination site scar Other: HIV negative No prior or concurrent extensive skin disorders (e.g., eczema, extensive psoriasis, burns, impetigo, disseminated zoster) No other serious medical condition that would preclude study participation No active infection requiring antibiotics Must be able to avoid close contact with children under 3 years old, pregnant women, individuals with eczema or other skin conditions, and immunosuppressed people for 2 weeks after each vaccination No seizures, encephalitis, or multiple sclerosis No allergy to eggs Not pregnant or nursing Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY: Biologic therapy: Prior vaccinia virus exposure required No other concurrent biologic therapy Chemotherapy: See Disease Characteristics At least 3 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin) Endocrine therapy: At least 3 weeks since prior hormonal therapy No concurrent steroids or hormonal therapy Radiotherapy: At least 3 weeks since prior radiotherapy No concurrent radiotherapy Surgery: No prior splenectomy Other: At least 3 days since prior antibiotics