Ductal carcinoma in situ (DCIS) accounts for approximately 20% of breast cancers and represents cancer cells confined within the normal structures of the breast. In up to 40% of patients, invasive breast cancer (IBC) develops with the potential to cause death. We cannot predict which DCIS will develop IBC and consequently all DCIS patients are treated as if it will. Our project proposes to analyse the National Breast Cancer Register for information pertaining to all DCIS cases. We will analyse this data using various statistical methods, with the priority to look for factors associated with NZ DCIS patients developing IBC. We will compare our findings to those from international studies. We will then build a statistical model to see if combining certain types of information can be used to predict the risk of DCIS developing IDC. The findings of this study may be useful in influencing clinical decisions in the future.