Rates of diabetes and cancer within our population are rising rapidly over time, and it is becoming increasingly common for one person to have both conditions. This is important because we know that diabetes can negatively impact access to, and through, the cancer treatment pathway. Crucially, this impact is likely to be most profound for Māori and Pasifika New Zealanders, for whom rates of diabetes and several common cancers are much greater than that experienced by other ethnic groups. In this study, we will first establish the current and likely future burden of cancer and diabetes co-occurrence using NZ Cancer Registry and Virtual Diabetes Register data, separately for Māori, Pasifika and non-Māori/non-Pasifika New Zealanders. Secondly, we will use breast cancer as an exemplar to investigate how diabetes affects cancer diagnosis, treatment and survival outcomes for Māori and Pasifika (and non-Māori/non-Pasifika) people, using high-quality National Breast Cancer Register data.