Quantifying Unmet Need and Structural Disparities in Stem Cell Transplantation

Samantha E. Watters, PhD, MPH, principal provider education and research partner at the National Marrow Donor Program (NMDP), discusses the research used to measure gaps in access to allogeneic hematopoietic cell transplantation across 3 key variables: unmet need, social vulnerability, and physician density. In an article she coauthored in JCO Oncology Practice, Watters used an analytical model that combines national health registries, cancer surveillance data, and demographic indices to pinpoint geographic and structural disparities in transplant access at the county level.

Calculating unmet need requires contrasting actual transplant utilization against theoretical disease demand. Actual utilization data is derived from the Stem Cell Therapeutic Outcomes Database, administered by the Center for International Blood and Marrow Transplant Research across a global network of over 450 transplant centers. To estimate theoretical need, researchers integrate disease incidence rates from the National Cancer Institute's Surveillance, Epidemiology, and End Results dataset, published non-malignant disease estimates, and US Census Bureau population data.

Determining clinical eligibility relies on disease-specific literature, subject matter expert consultations, and National Comprehensive Cancer Network (NCCN) guidelines. Because individual county numbers can be small, these metrics are aggregated over a 5-year period per 100,000 population to produce a standardized percent unmet need rate.

To analyze how socioeconomic and healthcare infrastructure factors correlate with this unmet need, the study incorporates two additional county-level metrics:

• Social Vulnerability Index (SVI): developed by the CDC, this composite index evaluates 16 variables across 4 core themes: socioeconomic status, race/ethnicity, housing/transportation vulnerability, and household characteristics, to establish an overall social vulnerability indicator for each county.
• Physician Density: quantified specifically for this study, this variable calculates the number of hematology, oncology, and transplant physicians per 10,000 residents in each county, directly identifying “physician deserts” lacking diagnostic and specialized transplant capabilities.

By evaluating the interplay among unmet need, social vulnerability, and specialist density, the research provides a framework for identifying systemic barriers to cell therapy care.