Cancer can be a major cause of poverty. This may be due either to the costs of treating and managing the illness as well as its impact upon people's ability to work. This is a concern that particularly affects countries that lack comprehensive social health insurance systems and other types of social safety nets. The ACTION study is a longitudinal cohort study of 10,000 hospital patients with a first time diagnosis of cancer. It aims to assess the impact of cancer on the economic circumstances of patients and their households, patients' quality of life, costs of treatment and survival. Patients will be followed throughout the first year after their cancer diagnosis, with interviews conducted at baseline (after diagnosis), three and 12 months. A cross-section of public and private hospitals as well as cancer centers across eight member countries of the Association of Southeast Asian Nations (ASEAN) will invite patients to participate. The primary outcome is incidence of financial catastrophe following treatment for cancer, defined as out-of-pocket health care expenditure at 12 months exceeding 30% of household income. Secondary outcomes include illness induced poverty, quality of life, psychological distress, economic hardship, survival and disease status. The findings can raise awareness of the extent of the cancer problem in South East Asia and its breadth in terms of its implications for households and the communities in which cancer patients live, identify priorities for further research and catalyze political action to put in place effective cancer control policies.