The drug therapy of breast cancer includes endocrine therapy, cytotoxic chemotherapy, targeted therapy and more recently, immunotherapy. These have been developed based on tumor biological characteristics and so they are directed towards various molecular and cellular targets which are involved in tumor growth, survival and spread. The rationale behind endocrine therapy is that the drugs are able to influence the level of endogenous estrogen and also interfere with its interaction with the estrogen receptor. Targeted therapy is a widely studied class of breast cancer chemotherapy as the drugs which belong to this group are directed towards specific cellular and extracellular proteins which are involved in the pathogenesis of breast cancer. Even more recently developed are the immunotherapeutic agents which are able to induce tumor regression by enabling the immune system to recognise tumor-associated antigens as well as regulating various immunomodulatory signals.