The ultimate goal of cancer therapy is to eradicate all tumour cells. The magnitude of the challenge is illustrated in Figure 2.1A. At diagnosis, the volume of a patient's cancer may be in the range of 10¹² cells in cases of extensive disease. Achieving this degree of tumour cell kill with cytotoxic chemotherapy is extraordinarily difficult at tolerated doses.^1,2  Combination chemotherapy, first developed by Emil “Tom” Frei and others using agents with non-overlapping toxicity profiles,^1,2  was able to increase the period of complete remission (i.e., to a cancer volume below the level of detection; perhaps 10¹⁰ cancer cells), and has become the mainstay of cancer treatment.²  However, long-term clinical benefit is rarely achieved by combination chemotherapy in adult patients with disseminated or metastatic disease.