smoking

Treatment is rarely the only cause of a second cancer, and in adults it is usually not the main one. Smoking is the clearest example: after chest radiotherapy for Hodgkin lymphoma, the risks from tobacco and from treatment appeared to multiply rather than add, which makes stopping smoking the largest single lever a survivor has over this particular risk.

Lung cancer is the commonest cause of death among people who develop a second cancer, and chest radiotherapy raises the risk of it for more than twenty years. There is no screening programme aimed at survivors anywhere, although some survivor groups have a measured rate above the threshold at which lung screening was shown to save lives, so this is a gap rather than a settled answer.