Why is cancer drug discovery so difficult?

Oncology has a higher rate of attrition in clinical development than most other therapeutic areas. Lengauer and colleagues discuss the factors responsible, and suggest strategies to improve the chances of short-term success in the development of novel anticancer drugs. Thirty-five years after the 'war on cancer' was declared, the discovery of anticancer drugs remains a highly challenging endeavour. Here, we consider the factors responsible, such as tumour heterogeneity, and suggest strategies to improve the chances of short-term success in the development of novel anticancer drugs.