Recent years have witnessed major advances in breast cancer medicine, including targeted drug therapies and the expansion of multidisciplinary centers for treatment and translational research. Yet the impact of these advances has been limited by continued differences in the delivery of care, both within countries and between them. Currently, ascertaining a direct causal relation between differences in the delivery of care and differences in cancer outcomes is difficult.1-3 Nevertheless, it is important to develop a clearer understanding of the factors that influence the receipt of breast cancer treatment. There are several reasons for this: 1) advances in the effectiveness of treatment are likely to make differences in the time to diagnosis and treatment more significant; 2) a smooth progression of care may improve the experience of patients, which, in itself, is a key aspect of the delivery of care; and 3) the growth of multidisciplinary centers worldwide will intensify the need for coordination among diverse practitioners and departments.In this issue of Cancer, 4 investigators Unger-Saldaña et al report on system delays in receipt of breast cancer treatment. Specifically, the authors use time intervals, a paradigm applied in other studies of health care system delay, 5-7 to assess the duration between symptom appreciation and presentation (person interval) and the duration between first consultation, confirmation of diagnosis, and the start of treatment (system intervals). Through a robust multivariate regression analysis of 886 women with breast cancer who attended 4 public specialty centers in Mexico City, Unger-Saldaña et al demonstrate that both patient and provider delays are responsible for a high burden of advanced-stage (III and IV) breast cancers at diagnosis (48%). But what is most striking about these findings is the proportion of delay identified at the system level. Although the total median time between symptom appreciation and the start of treatment was 7 months, the largest delay (4 months) took place between the first primary care consultation and the confirmation of diagnosis. These findings correspond to results from previous studies of cancer system delay in Mexico. 6 Bright et al observed a similarly large burden of delay concentrated in the referral interval, in which patients experienced an average of 6 months between the time of their first presentation to a primary care provider and diagnostic confirmation at the tertiary level.There is considerable debate about what constitutes a harmful delay in initiation of breast cancer treatment. 2,3,8,9