Whitney Zahnd, Ph.D
Post-Doctoral Fellow
South Carolina Rural & Minority Health Research Center at the University of South Carolina
The Delta Regional Authority (Delta Region) is a federally designated region of 252 counties and parishes in the eight state Lower Mississippi Delta Region (LMDR) states. More than one in five residents in the Delta Region live below the poverty line, and roughly one-third of residents are black. Further, more than forty percent of Delta Region counties are rural, and more than ninety percent of counties are designated as health provider shortage areas. All of these characteristics make the region vulnerable to numerous health disparities—including breast cancer disparities. The Delta Region overall has a higher breast cancer mortality rate than the rest of the country, and nine of the top ten counties for breast cancer mortality rates are in the Delta Region.
The Delta Region is relatively understudied aside from a few studies evaluating cancer mortality and screening. However, NAACCR’s Cancer in North America (CiNA) Deluxe dataset proved to be a great, high-quality source of population-level cancer data to examine breast cancer incidence and staging across the LMDR states, broadly, and within the Delta Region specifically. As described in the abstract below and in the linked dissertation, we were able to explore the disparities in subtype and staging between the Delta Region and non-Delta Region of the LMDR states and between black and white women in the Delta Region for two of the study’s aims.
Seven of the LMDR states (Alabama, Arkansas, Illinois, Kentucky, Louisiana, Mississippi, and Tennessee) provided active consent for their CiNA Deluxe data to be used in this study. This rich dataset not only included demographic information and breast cancer stage but also the collaborative stage site-specific factors necessary to determine the breast cancer subtype of each breast cancer. Understanding breast cancer subtype is instructive as each subtype varies by detectability through regularly screening mammography, treatment regimens, and prognoses. For example, our study found that Delta Region women had higher triple-negative breast cancer incidence rates than women in the non-Delta Region. Although this is to be expected because of the racial composition of the Delta Region, it may also help explain the elevated mortality rate due to breast cancer as triple-negative breast cancer has the worst prognosis of all subtypes.
CiNA Deluxe data were an excellent resource to help elucidate cancer disparities across a multi-state region. The fastidious work of cancer registry staff and cancer registrars in the LMDR states provided high quality, population-based data for this study. Thanks also to Drs. Susan Farner, Hillary Klonoff-Cohen, Sara McLafferty, Recinda Sherman, and Karin Rosenblatt for their expertise.
Click here to view Zahnd Dissertation 2018
Abstract
The Delta Regional Authority (Delta Region) is a federal-state partnership aiming to improve socioeconomic conditions in 252 counties and parishes in the eight state Lower Mississippi Delta Region (LMDR). The Delta Region has a higher proportion of black residents, is poorer, and is more rural than the country as a whole. It also has far higher breast cancer mortality rates than the nation. Black women in the Region have higher breast cancer mortality rates than white women in the Delta Region and have higher breast cancer mortality rates than black women in other parts of the country. More aggressive breast cancer subtypes, more advanced stage at diagnosis, and less access to screening mammography may play a role in these high mortality rates. Studies have shown that black women have higher rates of the most aggressive breast cancer subtype– triple-negative–than white women and are often diagnosed at a more advanced stage. Additionally, while poor and rural women tend to have lower incidence rates of breast cancer, they often have a higher odds of late-stage cancer and less access to screening services.
This dissertation sought to elucidate the Delta Region’s breast cancer mortality disparity by determining differences between the Delta and non-Delta Regions of the LMDR and by exploring racial differences within the Delta Region among the following areas: breast cancer subtype, breast cancer staging, and spatial access to mammography services. Population-based cancer surveillance data from the North American Association of Central Cancer Registries were analyzed to determine age-adjusted, subtype-specific incidence rates and rate ratios in the Delta and non-Delta Regions of the LMDR. Multilevel negative binomial regression models were constructed to evaluate if identified disparities were attenuated after accounting for race/ethnicity, age, and contextual factors. These analyses were performed for all cases by subtype and separately for early stage and late stage cancers by subtype. Higher rates of triple-negative breast cancer were identified in the Delta Region compared to the non-Delta Region, but this was attenuated in multivariable models. However, triple-negative breast cancer rates were higher in the urban Delta compared to the urban non-Delta, even after accounting for race/ethnicity, age, and contextual factors. Black residents in the Delta Region had higher rates of hormone receptor-negative breast cancers and higher rates of breast cancer overall compared to white women in the Region. Further, there were no particularly notable differences in late-stage breast cancers between the Delta and non-Delta Regions. However, black women in the Delta Region had lower rates of early-stage breast cancer, but higher rates of late-stage breast cancers compared to white, Delta Region women, even after accounting for age and contextual factors.
To evaluate spatial access to mammography services, this study applied the enhanced two-step floating catchment area method to Food and Drug Administration data and census tract level American Community Survey data. The Food and Drug Administration data provided addresses of all approved mammography facilities in the LMDR and adjacent states while American Community Survey data were used to estimate populations of women of recommended screening age at the census tract level. For the most part, women in the Delta Region had similar spatial access to mammography services as non-Delta Region women. However, clusters of low spatial access within the Delta Region were identified in parts of Arkansas, Tennessee, and Mississippi.
The identified higher incidence of breast cancer in black women in the Delta compared to white women was driven by higher rates of hormone receptor-negative cancers, but further research is needed to determine what individual or contextual factors may be driving the higher incidence rates. Additionally, this dissertation underscores the importance of community-based, culturally tailored interventions to improve mammography utilization rates and subsequently improve early detection of hormone receptor-positive breast cancers. Furthermore, this dissertation signaled a need for improved state-level policy and geographically targeted regional resource allocation to improve screening access and utilization. Additionally, these findings provide the foundation for further research to explore regional breast cancer disparities at other points along the cancer control continuum (e.g. treatment), to examine regional disparities for other cancers, and to promote collaborative academic partnerships across the Delta Region.
