Solid tumours consist of a complex network of blood vessels surrounded by normal and malignant cells. They pose a particular challenge in the effort to develop anti-cancer drugs because malignant cell growth results in the development of regions in solid tumours that are resistant to radiation therapy. Anti-cancer drugs must overcome the barriers this environment poses, but there are currently no standard techniques for assessing a drug’s penetration in tumours. Alastair Kyle is addressing that gap by studying two techniques to examine the penetration of existing and new anti-cancer drugs. A better understanding of drug penetration in solid tumours could lead to the development of drugs that are more effective in entering the tumour. It could also lead to new insights into ways of modifying the tumour itself to make it more susceptible to specific cancer drugs.