Abstract: Cancer is a systems biology disease. Cancer systems biology uses high-throughput technologies and computational modeling to understand the biological behavior of cancer, identify cancer biomarkers, and propose new cancer treatment strategies. The integration of high-throughput "omics" data from cancer tissues and blood preparations, together with new systems approach for cancer diagnostics, enables the identification of cancer biomarkers, classification of cancer, evaluation of cancer progression and patient response to treatment, as well as prediction of recurrence and metastasis. Moreover, systems biology can develop personalized medicine and systemic therapy in oncology. System approaches have great potential in cancer diagnosis and treatment. A substantial progress in understanding cancer using systems biology will ultimately lead to the development of clinical oncology. Systemic therapies based on systems biology are critical to the battle against cancer.