Prior studies of allogeneic hematopoietic cell transplantation (HCT) therapy for the treatment of malignant or nonmalignant blood disorders assume a 30% likelihood that a patient will find a match among siblings and, therefore, a 70% likelihood of needing an unrelated donor source. This study utilizes birth data and statistical modeling to assess the adequacy of these estimates to describe the probability among US population cohorts segmented by race/ethnicity and age, including ages of greatest HCT utilization. Considerable variation in the likelihood of an HLA-identical sibling was found, ranging from 13% to 51%, depending upon patient age and race/ethnicity. Low sibling match probability, compounded with increased genetic diversity and lower availability among unrelated donors, put the youngest minority patients at the greatest risk for not finding a suitable related or unrelated HCT donor. Furthermore, the present 40-year decline in birth rates is expected to lead to 1.5-fold decrease in access to a matched sibling for today's young adults (18 to 44 years of age) when they reach peak HCT utilization years (near age 61 years) versus their contemporary adult counterparts (44 to 64 years). Understanding the sibling match probability by race/ethnicity and age cohort leads to forecasting the demand for unrelated HCT sources.

Purpose: Allogeneic hematopoietic cell transplantation (HCT) is an increasingly used therapy for many patients with hematologic malignancies and other marrow failure or immune system disorders. The purpose of this study was to quantify and visualize both the demand and unmet need for HCT. Methods:HCT use for 2012 was described using the Center for International Blood and Marrow Transplant Research registry. Potential demand for HCT was calculated using 2012 SEER data and published literature for HCT-treatable conditions. Point locations of transplant centers were geocoded using geographic information system (GIS) software; Thiessen polygons were created to establish adult (age 20 to 74 years) and pediatric (age 0 to 19 years) market areas. Market-area population estimates were calculated using 2012 population estimates by age aggregated by census block. Results: US market areas for HCTs were identified separatelyfor transplant centers treating adult (n ϭ 62) and pediatric patients (n ϭ 52). Overall HCT demand among adults was 16,096, with an unmet need for HCTs of 10,276 patients. For pediatric patients, the total demand was 4,561, with an unmet need of 3,213 potential recipients. Evaluation of adult and pediatric market areas indicated that the largest unmet needs tended to be in areas with large populations. Conclusion:Market-area maps and statistics developed using GIS will help communicate the unmet need for HCT, inform policy, and assist transplant centers in planning for the anticipated growth in HCT use.

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