Novel systemic therapies for breast cancer.

The rapid expansion in our knowledge of the molecular pathogenesis of cancer has created several opportunities for novel strategies in anti-cancer drug design and development. Recent developments have included a series of new endocrine therapies such as pure anti-oestrogens and selective oestrogen receptor modulators, and trials are in progress to determine their role in the sequence of therapies given the first-line role now occupied by the aromatase inhibitors. Novel cytotoxic drugs have been developed with an improved toxicity profile, including oral prodrugs that are activated within tumour cells, and liposomal delivery mechanisms for conventional drugs that reduce some of the systemic toxicities. There has been much success with monoclonal antibodies targeted against growth factor receptors, both as monotherapy and in enhancing the efficacy of cytotoxic drugs. A number of small molecule signal transduction inhibitors are in early stages of clinical development for breast cancer, including tyrosine-kinase inhibitors and farnesyl transferase inhibitors. Emerging pre-clinical evidence suggests that these drugs may best be used in combination with endocrine therapy. Other novel strategies that are being tested include vaccines and anti-angiogenesis drugs. As these new therapies evolve towards the clinic, the challenge to oncologists is whether their potential seen in the laboratory can be matched by further substantial improvements in clinical outcome.