91 Musa Mayer1 1 AdvancedBC.org, Abstract To advocate most effectively for a population of patients, they must be accurately described and the course of the disease must be well characterized. Accurate epidemiologic statistics are currently lacking for the MBC population. Methods: We reviewed the availability of epidemiologic data related to MBC and the nature of those data. Results: The NCI SEER registries collect only incidence at first diagnosis, initial treatment, and mortality. Recurrent cancer is not tracked; the data on MBC are limited. While creative methods have been used to estimate the number of new cases of MBC and the number of those currently living with the disease, more accurate estimates of MBC incidence and prevalence do not currently exist. The modest increase in duration of MBC survival that has been documented over the past few decades has been observed primarily in ER+ and/or HER2+ MBC and appears to be attributable to the wide use of targeted therapies. During this time frame, the disparity between survival among black women with MBC and non-Hispanic white women with MBC has been increasing. Conclusions: Accurate epidemiologic information is needed to accurately and effectively demonstrate the need for services and plan and fund the application of services. Why Do Accurate Statistics Matter? To advocate most effectively for a population of patients, they must be accurately described and the course of the disease must be well characterized. Accurate epidemiologic statistics are currently lacking for the MBC population. Epidemiologic studies are needed to inform discussions about the size and characteristics of the MBC patient population as well as the numbers and types of resources and services needed. A true picture of the number of new cases each year and the number of people living with MBC could encourage drug development. Studies should also include analysis of trends in incidence and length of survival for future planning and investigations of the natural history of MBC to allow for evaluation of the impact of new interventions. Of particular concern for advocates is having a realistic picture of the impact of emerging research on the issues that matter most to patients. For example, new drugs for MBC represent a source of hope that patients can live longer or even be cured. But do these drugs actually extend life or just increase health care costs? Do they improve quality of life? Other related research questions include: How many new cases of MBC are diagnosed each year? How representative of the whole MBC population are patients in clinical trials? Does delaying cancer progression mean that overall survival is improved? What problems do MBC patients have with obtaining treatment, given existing co-payment and treatment access programs, and what impact does this have on MBC survival? Currently there are no population-based data-collection systems that can answer these questions. To advocate for a population of patients, they must be accurately described and the course of the disease must be well characterized. Chapter 5: Epidemiology of MBC— Challenges with Population-Based Statistics