The pretargeting approach using bispecific affibody-antibody complex (BAAC) and targeting of chemotherapeutic drug loaded polymers have been used in breast cancer cell cultures to demonstrate targeted chemotherapy and reduce toxicity to non-pretargeted cancer and cardiac cells. HER2/neu-positive BT-474 and -negative BT-20 human mammary carcinoma cell lines were pretargeted with BAAC and targeted with multi-doxorubicin (Dox) loaded polyglutamic acid (PGA) site specifically modified with diethylene triamine pentaacetic acid (DTPA) (D-Dox-PGA) at the N-terminal of PGA. Toxicity to embryonic cardiocytes and human mammary carcinoma cells were assessed. BAAC was prepared by covalent conjugation of anti-HER2/neu affibody and anti-DTPA Fab via the thioether linkage. N-terminal DTPA modified polyglutamic acid was conjugated with doxorubicin via the amide bonds. Reduction in cardiotoxicity and IC50 of D-Dox-PGA and free Dox were determined in embryonic cardiocyte H9C2 cultures. Enhanced targeted tumor toxicity was demonstrated in BT-474 human mammary carcinoma cell line pretargeting with BAAC followed by targeting with D-Dox-PGA and compared to D-Dox-PGA alone with no pretargeting or free Dox. No enhanced targeted tumor toxicity was observed in HER2/neu negative BT-20 cells. IC50 of D-Dox-PGA and free Dox on embryonic cardiocytes was 15.75 and 1.20 μg/ml, respectively. When BT-474 and BT-20 cells were pretargeted with BAAC followed by targeting with D-Dox-PGA, higher tumor cell-killing was seen only in BT-474 cells. Pretargeting with BAAC resulted in greater tumor cell death in BT-474 human breast cancer cells due to specific targeted delivery of D-Dox-PGA than cancer cells treated with D-Dox-PGA without pretargeting or treatment with free doxorubicin. In vitro targeted delivery of polymer drug conjugate resulted in highly specific, targeted HER2/neu positive BT-474 cancer cell death. Such a pretargeting and targeting approach using prodrug polymers may allow development of very efficient, lower non-target toxicity, and image-guided targeted therapy since these polymers can also be labeled with radioisotopes.