Volume 116, Issue 14 p. 3469-3476
Original Article
Free Access

Access to hematopoietic stem cell transplantation

Effect of race and sex

Thomas V. Joshua MS

Corresponding Author

Thomas V. Joshua MS

Center for Nursing Research, School of Nursing, Medical College of Georgia, Augusta, Georgia

Fax: (706) 721-7049

Center for Nursing Research, School of Nursing, Medical College of Georgia, 987 St. Sebastian Way, EC-4410, Augusta, GA 30912===Search for more papers by this author
J. Douglas Rizzo MD, MS

J. Douglas Rizzo MD, MS

Center for International Blood and Marrow Transplant Research, Medical College of Wisconsin, Milwaukee, Wisconsin

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Mei-Jie Zhang PhD

Mei-Jie Zhang PhD

Department of Biostatistics, Medical College of Wisconsin, Milwaukee, Wisconsin

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Parameswaran N. Hari MD, MS

Parameswaran N. Hari MD, MS

Center for International Blood and Marrow Transplant Research, Medical College of Wisconsin, Milwaukee, Wisconsin

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Seira Kurian MD, MS, MPH

Seira Kurian MD, MS, MPH

Los Angeles County Department of Public Health, Los Angeles, California

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Marcelo Pasquini MD, MS

Marcelo Pasquini MD, MS

Center for International Blood and Marrow Transplant Research, Medical College of Wisconsin, Milwaukee, Wisconsin

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Navneet S. Majhail MD, MS

Navneet S. Majhail MD, MS

Department of Hematology/Oncology, University of Minnesota, Minneapolis, Minnesota

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Stephanie J. Lee MD, MPH

Stephanie J. Lee MD, MPH

Department of Hematology/Oncology, Fred Hutchinson Cancer Center, Seattle, Washington

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Mary M. Horowitz MD, MS

Mary M. Horowitz MD, MS

Center for International Blood and Marrow Transplant Research, Medical College of Wisconsin, Milwaukee, Wisconsin

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First published: 24 May 2010
Citations: 114

Abstract

BACKGROUND:

The purpose of the current study was to determine whether the use of hematopoietic stem cell transplantation (HCT) to treat leukemia, lymphoma, or multiple myeloma (MM) differs by race and sex.

METHODS:

The annual incidence of leukemia, lymphoma, and MM was estimated in the United States in people aged <70 years by race and sex using the Surveillance, Epidemiology, and End Results (SEER) cancer registry between 1997 and 2002 and US census reports for the year 2000. The annual incidence of autologous, human leukocyte antigen (HLA) identical sibling, and unrelated HCT performed in these groups was estimated using Center for International Blood and Marrow Transplant Research data from 1997 through 2002. Logistic regression analysis was used to calculate the age-adjusted odds ratio (OR) of receiving HCT for Caucasians versus African Americans and for men versus women.

RESULTS:

The likelihood of undergoing HCT was found to be higher for Caucasians than for African Americans (OR, 1.40; 95% confidence interval [95% CI], 1.34-1.46). This difference existed for each type of HCT: autologous (OR, 1.24; 95% CI, 1.19-1.30), HLA identical sibling (OR, 1.59; 95% CI, 1.46-1.74), and unrelated donor (OR, 2.02; 95% CI, 1.75-2.33). Overall, men were more likely than women to receive HCT (OR, 1.07; 95% CI, 1.05-1.1 [P < .0001]); however, this difference was found to be significant only for autologous HCT (OR, 1.10; 95% CI, 1.07-1.13 [P < .0001]).

CONCLUSIONS:

HCT is more frequently used to treat leukemia, lymphoma, and MM in Caucasians than in African American individuals. African Americans have lower rates of both autologous and allogeneic HCT, indicating that donor availability cannot fully explain the differences. Women are less likely than men to receive autologous HCT for reasons unexplained by age or disease status. Cancer 2010. © 2010 American Cancer Society.

Hematopoietic stem cell transplantation (HCT) is a relatively new treatment modality. Its history began in the late 1940s and early 1950s, when animal studies revealed the ability of donor bone marrow to restore hematopoiesis after irradiation.1 The first successful HCTs in humans were performed in 1968.2-4 Procedure volume has increased rapidly over the last few decades, with approximately 60,000 transplants performed worldwide in 2006.4 Although HCT has the potential to increase survival for patients with many diseases, particularly hematologic malignancies, it is an intensive, costly, and technically sophisticated procedure with a substantial risk of early morbidity and mortality.

Access to healthcare is defined as using affordable personal health services in a timely manner to achieve the best health outcomes possible.5 The process of gaining access to care includes dynamic interactions between individuals with diverse ethnic, cultural, and socioeconomic backgrounds; healthcare providers operating in a variety of practice patterns with external constraints; and healthcare systems.6 HCT is an important treatment option for patients with leukemia, lymphoma, and related disorders, offering the best chance for cure in several clinical situations.4, 7, 8 Limitations in access to this procedure have substantial clinical, ethical, and policy implications.

Considerable variation exists in the distribution of health and healthcare in the United States. In 2002, the Institute of Medicine published an authoritative report indicating that minorities are less likely than whites to receive needed routine and complex healthcare services across a broad array of diseases including cancer, cardiovascular disease, human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS), diabetes, and mental illness.9 Since that report, the Agency for Healthcare Research and Quality has published an annual National Healthcare Disparities Report (NHDR) to provide an overview of disparities in healthcare among racial, ethnic, and socioeconomic groups in the United States, and to track progress in reducing disparities.10 The 2006 NHDR suggested that disparities remain prevalent between men and women and among racial groups, including disparities in cancer care.11 Several studies have indicated that men receive more early cancer detection tests than women in the same practices,5, 12, 13 and cancer treatment outcomes are poorer in African Americans.9-14 Outcome disparities may be correlated with more advanced stage of disease at the time of diagnosis, a phenomenon believed to be primarily because of the underutilization of cancer screening. Some studies have suggested that lower socioeconomic status resulting in reduced access to healthcare may be a major explanation for racial differences in cancer mortality.15-25

The purpose of the current study was to determine whether the use of HCT to treat leukemia, lymphoma, or multiple myeloma (MM) differs by race and sex. We hypothesized that women and African Americans with these diseases are less likely to receive HCT. Although there may be regional differences in healthcare availability,26 this study examined utilization rates for the country as a whole.

MATERIALS AND METHODS

The Center for International Blood and Marrow Transplant Research (CIBMTR) database was used to estimate the annual number of HCTs performed in the United States between 1997 and 2002. Data from the Surveillance, Epidemiology, and End Results (SEER)27, 28 database and the US Census Bureau29 were used to estimate the annual total number of new cases of each disease in the US population in the same time period. By using these data, we estimated the rates (number of transplantations/number of patients with disease) of HCT performed for leukemia, lymphoma, and MM between 1997 and 2002.

The CIBMTR is a research program formed in July 2004 through an affiliation of the International Bone Marrow Transplant Registry and Autologous Blood and Marrow Transplant Registry of the Medical College of Wisconsin and the National Marrow Donor Program (NMDP). The CIBMTR is a voluntary consortium involving >500 transplant centers in 54 countries. These transplant centers worldwide contribute data regarding consecutive allogeneic and autologous HCTs to the CIBMTR. Participating centers are required to report all transplants consecutively and compliance is monitored through on-site audits. Computerized checks for errors, physician review of submitted data, and on-site audits of participating centers ensure the quality of the data. Patients are followed longitudinally, with yearly follow-up. The NMDP facilitates approximately 95% of all unrelated donor HCTs in the United States.

The SEER program of the National Cancer Institute27, 28 is an authoritative source of information regarding cancer incidence and survival in the United States. The SEER program collects and publishes cancer incidence and survival data from 14 population-based cancer registries and 3 supplemental registries covering approximately 26% of the US population.

Study Population

The population considered for this study included US patients aged <70 years with acute lymphoblastic leukemia (ALL), acute myelogenous leukemia (AML), chronic myelogenous leukemia (CML), non-Hodgkin lymphoma (NHL), and MM who were treated between 1997 and 2002; these are the most common disease indications for HCT. Patients aged >70 years were not considered because few transplants are performed in older patients.

Statistical Analysis

We calculated the annual number of incident cases of ALL, AML, CML, NHL, and MM per 100,000 persons based on the SEER population sampling frame between 1997 and 2002. First, incidence estimates were calculated from the SEER database separately for age group (ages birth-19 years, 20-29 years, 30-39 years, 40-49 years, 50-59 years, and 60-69 years), race (African American and Caucasian), and sex. This incidence rate was then applied to US Census Bureau (year 2000) estimates for numbers of persons in similar age, sex, and racial groups to derive an estimated annual number of patients with each disease in the US. The estimated annual numbers of autologous, human leukocyte antigen (HLA) identical sibling, and unrelated donor HCTs performed during the same time period, and for each sex, racial, and age group, were calculated by retrieving the number of transplants registered with the CIBMTR between 1997 and 2002. During this period, the CIBMTR collected an estimated 55% of autologous, 50% of HLA identical sibling, and >90% of unrelated donor HCTs performed in the US (estimation is described in more detail elsewhere).30, 31

Consequently, we applied an adjustment factor of 1.8 and 2.0, respectively, to the reported numbers of autologous and HLA identical sibling HCTs.

We then evaluated the rates of all HCTs as well as autologous, HLA identical sibling, and unrelated donor HCTs by race and sex, for all diagnoses, and for each disease separately using logistic regression analysis adjusting for age. The rates of HCTs were calculated by dividing the number of estimated procedures by the number of patients diagnosed with disease in the same age range. When multiple comparisons were made, the P value of significance was considered to be ≤.001 using Bonferroni adjustment.

In these analyses, we assumed that the sample of patients reported to the CIBMTR was representative of the total US population of HCT recipients. A sensitivity analysis was performed to assess the potential effect of selective under-reporting of HCT for African Americans on the results of this study. In the initial analysis, we assumed that 55% of all autologous HCTs and 50% of all allogeneic HCTs performed in the United States were reported to CIBMTR, regardless of patient race. Data were reanalyzed after increasing the number of autologous and HLA identical sibling transplants for African Americans reported to the CIBMTR by 5%, 10%, 15%, and 20%.

RESULTS

A total of 27,725 patients registered with the CIBMTR met our selection criteria. Of these, 15,363 (55%) underwent autologous HCT, 5731 (21%) underwent HLA identical sibling HCT, and 6631 (24%) underwent unrelated donor HCT. There were 25,068 (90%) patients classified as Caucasian and 2657 (10%) classified as African American. Approximately 59% were males. Pediatric patients represented only 10% of patients who underwent transplantation and among those, 81% of the transplants were for acute leukemia (AML and ALL). General characteristics of the HCT population are presented in Table 1. By using these data and the adjustment factors described earlier, we estimated that there were approximately 45,750 HCTs performed for the eligible diseases during the study period. During the same period of time, there were an estimated 273,853 patients diagnosed in the US with the diseases considered in this analysis.

Table 1. Characteristics of HCT Patients
Variables Caucasian No. (%) Evaluable African American No. (%) Evaluable Total (%)
No. of patients 25,068 (90) 2657 (10) 27,725
Sex
 Male 14,807 (59) 1443 (54) 16,250 (59)
 Female 10,261 (41) 1214 (46) 11,475 (41)
Year of transplant
 1997 3319 (13) 289 (11) 3608 (13)
 1998 3916 (16) 403 (15) 4319 (16)
 1999 4236 (17) 468 (18) 4704 (17)
 2000 4427 (18) 463 (17) 4890 (18)
 2001 4466 (18) 510 (19) 4976 (18)
 2002 4704 (19) 524 (20) 5228 (19)
Age group at transplant, y
 Birth-19 2282 (9) 370 (14) 2652 (10)
 20-29 1956 (8) 206 (8) 2162 (8)
 30-39 3261 (13) 406 (15) 3667 (13)
 40-49 5915 (24) 652 (25) 6567 (24)
 50-59 7491 (30) 684 (26) 8175 (29)
 60-69 4163 (17) 339 (13) 4502 (16)
Donor type
 Auto HCT 13,758 (55) 1605 (60) 15,363 (55)
 HLA sibling HCT 5230 (21) 501 (19) 5731 (21)
 Unrelated HCT 6080 (24) 551 (21) 6631 (24)
Disease
 AML 5247 (21) 458 (17) 5705 (21)
 ALL 2340 (9) 245 (9) 2585 (9)
 CML 2824 (11) 341 (13) 3165 (11)
 NHL 8936 (36) 546 (21) 9482 (34)
 MM 5721 (23) 1067 (40) 6788 (24)
Graft type
 Bone marrow 7544 (30) 635 (24) 8179 (30)
 Peripheral blood 16,985 (68) 1895 (71) 18,880 (68)
 Cord blood 539 (2) 127 (5) 666 (2)
  • HCT indicates hematopoietic stem cell transplantation; Auto HCT, autologous HCT; HLA sibling HCT, human leukocyte antigen identical sibling HCT; AML, acute myelogenous leukemia; ALL, acute lymphoblastic leukemia; CML, chronic myelogenous leukemia; NHL, non-Hodgkin lymphoma; MM: multiple myeloma.

Effect of Race

Overall effect of race

Compared with African Americans, the age-adjusted odds ratio (OR) of undergoing any type of HCT for all diseases considered was higher for Caucasians (OR, 1.40; 95% confidence interval [95% CI], 1.35-1.46 [P < .0001]). A significantly higher OR of receiving HCT was noted for each type of HCT: autologous (OR, 1.24; 95% CI, 1.19-1.30 [P < .0001]), HLA identical sibling (OR, 1.59; 95% CI, 1.46-1.74 [P < .0001]), and unrelated donor (OR, 2.02; 95% CI, 1.75-2.33 [P < .0001]) (Table 2). Sensitivity analyses suggested that the results of this study were robust, even in the conditional setting of 20% under-reporting of HCTs in African Americans (OR, 1.15; 95% CI, 1.10-1.20). There were some differences observed by disease.

Table 2. Age-Adjusted OR of Receiving HCT by Race and Sex
Estimated Annual US Incidence Estimated Annual HCTs in the US Transplant Types HCT Types and ORs Caucasians Versus African Americans HCT Types and ORs Males Versus Females
OR (95% CI) P OR (95% CI) P
All diseases 45,643 7623 Overall HCT 1.40 (1.35-1.46) <.0001 1.07 (1.05-1.1) <.0001
4608 Autologous HCT 1.24 (1.19-1.30) <.0001 1.10 (1.06-1.13) <.0001
1910 HLA identical sibling HCT 1.59 (1.46-1.74) <.0001 1.05 (0.99-1.10) .063
1105 Unrelated donor HCT 2.02 (1.75-2.33) <.0001 0.94 (0.88-1.01) .11
ALL 3508 580 Overall HCT 1.01 (0.81-1.25) .97 1.08 (0.96-1.21) .21
40 Autologous HCT 0.74 (0.42-1.28) .28 0.7 (0.49-0.98) .04
262 HLA identical sibling HCT 0.93 (0.69-1.24) .61 1.17 (0.99-1.38) .06
278 Unrelated donor HCT 1.23 (0.87-1.73) .24 1.08 (0.90-1.28) .42
AML 5032 1459 Overall HCT 1.52 (1.35-1.71) <.0001 0.83 (0.78-0.88) <.0001
363 Autologous HCT 1.08 (0.90-1.3) .40 0.77 (0.69-0.85) <.0001
694 HLA identical sibling HCT 1.44 (1.23-1.69) <.0001 0.91 (0.83-0.99) .021
402 Unrelated donor HCT 2.29 (1.74-3.02) <.0001 0.87 (0.77-0.98) .017
CML 2231 744 Overall HCT 1.42 (1.23-1.64) <.0001 0.90 (0.82-0.98) .018
22 Autologous HCT 2.36 (0.99-5.64) .05 1.17 (0.77-1.78) .46
413 HLA identical sibling HCT 1.25 (1.05-1.49) .01 0.89 (0.80-0.99) .041
309 Unrelated donor HCT 1.45 (1.16-1.81) .001 0.92 (0.81-1.05) .21
NHL 27,960 2804 Overall HCT 2.12 (1.95-2.29) <.0001 1.22 (1.17-1.26) <.0001
2273 Autologous HCT 2.03 (1.86-2.22) <.0001 1.18 (1.13-1.23) <.0001
428 HLA identical sibling HCT 2.23 (1.89-2.79) <.0001 1.45 (1.31-1.60) <.0001
103 Unrelated donor HCT 3.14 (1.79-5.53) <.0001 1.03 (0.84-1.27) .77
MM 6912 2036 Overall HCT 1.75 (1.64-1.86) <.0001 1.1 (1.05-1.15) <.0001
1910 Autologous HCT 1.72 (1.62-1.83) <.0001 1.1 (1.05-1.15) .0001
113 HLA identical sibling HCT 1.55 (1.21-1.98) .0006 1.03 (0.86-1.23) .77
13 Unrelated donor HCT 3.24 (1.24-8.50) .016 1.64 (0.94-2.86) .08
  • OR indicates odds ratio; HCT, hematopoietic stem cell transplant; 95% CI, 95% confidence interval; HLA, human leukocyte antigen; ALL, acute lymphoblastic leukemia; AML, acute myelogenous leukemia; CML, chronic myelogenous leukemia; NHL, non-Hodgkin lymphoma; MM, multiple myeloma.

Effect of race by disease and type of HCT

The OR of undergoing HCT for MM was higher for Caucasians than for African Americans (OR, 1.75; 95% CI, 1.64-1.86 [P < .0001]) (Table 2). This difference was observed for autologous HCT (OR, 1.72; 95% CI, 1.62-1.83 [P < .0001]), HLA identical sibling HCT (OR, 1.55; 95% CI, 1.21-1.98 [P = .0006]), and unrelated donor HCT (OR, 3.24; 95% CI, 1.24-8.50 [P = .016]). The OR of undergoing HCT for NHL was higher for Caucasians than for African Americans (OR, 2.12; 95% CI, 1.95-2.29 [P < .0001]). This difference was noted for autologous HCT (OR, 2.03; 95% CI, 1.86-2.22 [P < .0001]), HLA identical sibling HCT (OR, 2.23; 95% CI, 1.89-2.79 [P < .0001]), and unrelated donor HCT (OR, 3.14; 95% CI, 1.79-5.53 [P < .0001]). The OR of undergoing HCT for CML was higher for Caucasians than for African Americans (OR, 1.42; 95% CI, 1.23-1.64 [P < .0001]). This difference was noted for HLA identical sibling HCT (OR, 1.25; 95% CI, 1.05-1.49 [P = .01]) and unrelated donor HCT (OR, 1.45; 95% CI, 1.16-1.81 [P = .001]). Few patients (n = 22) received autologous HCT. The OR of undergoing HCT for AML was higher for Caucasians than for African Americans (OR, 1.52; 95% CI, 1.35-1.71 [P < .0001]). This difference was noted for HLA identical sibling HCT (OR, 1.44; 95% CI, 1.23-1.69 [P < .0001]) and unrelated donor HCT (OR, 2.29; 95% CI, 1.74-3.02 [P < .0001]), but not for autologous HCT (OR, 1.08; 95% CI, 0.90-1.3). There was no difference noted with regard to the OR of undergoing HCT for ALL between Caucasians and African Americans (OR, 1.01; 95% CI, 0.81-1.25 [P = .97]).

Effect of Sex

Overall effect of sex

Overall, men were more likely than women to receive HCT (OR, 1.07; 95% CI, 1.05-1.1 [P < .0001]). This difference was significant for autologous HCT (OR, 1.10; 95% CI, 1.06-1.13 [P < .0001]) but not for HLA identical sibling (OR, 1.05; 95% CI, 0.99-1.10 [P = .06]) or unrelated donor HCT (OR, 0.94; 95% CI, 0.88-1.01 [P = .11]), and there were significant differences by disease. In particular, men were more likely than women to undergo autologous HCT for MM or NHL.

Effect of sex by disease and type of HCT

The OR of undergoing HCT for AML was lower for males than females; this difference was significant in all transplant types (Table 2). The OR of undergoing HCT for CML was lower for males than females; this difference was significant for HLA identical sibling HCT but not for autologous or unrelated donor HCT. The OR of undergoing HCT for NHL was higher for males than for females; this difference was significant for autologous and HLA identical sibling HCT but not for unrelated donor HCT. The OR of undergoing HCT for MM was higher for males than females; this difference was significant for autologous but not for HLA identical sibling or unrelated donor HCT. There was no difference noted in the OR of undergoing HCT for ALL between males and females.

Affect of Adult Versus Pediatric Age Group

There were 2652 patients aged <20 years who were registered with the CIBMTR and met our selection criteria in the study period. The majority of these children had AML or ALL. We estimated that there were approximately 2955 HCTs performed for the eligible diseases during the study period. During the same period of time, there were an estimated 18,595 patients aged <20 years diagnosed in the United States with the diseases considered in this analysis. There were no significant differences by race and sex to report (data not shown) for this age group.

Interaction of Sex and Race

We tested for interactions between sex and race by comparing the overall and disease-specific OR of undergoing HCT in males versus females adjusting for race, and by comparing the odds of HCT in Caucasians versus African Americans, adjusting for sex. No significant interactions were evident.

DISCUSSION

Decision-making regarding the performance of HCT involves a complex interplay of factors. In general, categories of factors that may explain disparities in applied therapy include biologic factors (intrinsic variability in disease natural history or response to therapy), patient factors (presence of comorbidities that prevent application of therapy and patient preferences), healthcare systems factors (health insurance and availability of healthcare facilities), and care process or discrimination factors (provider attitudes such as bias against minorities, greater clinical uncertainty when understanding minorities' symptoms and severity, or preconceived beliefs regarding minority behavior or health). Ideally, clinical needs and appropriateness, biologic factors, and patient preferences should be the only considerations driving the therapeutic decision-making process. We assume that patient-related (other than preferences) and disease-related clinical factors do not vary by race and sex such that indications for HCT are not dramatically different in different racial and sex groups. We believe this is a reasonable assumption based on what is known about the diseases included in these analyses. The findings of the current study suggest a disparity in the rates of autologous and allogeneic HCT for African Americans and females that should cause concern, with the greatest disparity observed based on race. The rates of HCT were higher in Caucasians than in African Americans in nearly all subgroups examined, with ORs >2 in some categories.

Disparity in care could represent either underutilization in African Americans or overutilization in Caucasians. It could also be attributed to biologic differences. For example, the greater distribution of HLA types in African Americans and the smaller number of African Americans in volunteer donor registries make it more difficult to find suitably matched donors for African Americans in need of unrelated donor HCT. This may contribute to the lower rate of unrelated donor HCTs noted in this group. However, MM is a common indication for HCT. The preferred type of HCT for this disease is autologous, and during the 5-year time period spanned by the current study, it became the most common indication for autologous HCT.31 MM is twice as common in African Americans compared with Caucasians, but the ORs of undergoing HCT for MM were found to be 72% higher for Caucasians. These lower rates of autologous HCT suggest that the disparity is best explained by underutilization of HCT in African Americans and cannot be wholly attributed to donor availability.

The disparity in the use of HCT in men compared with women is less consistent than the disparity in use by race, with ORs closer to 1 and an increased OR noted in men for some diseases and in women for others. A unifying hypothesis for these differences is difficult to devise.

There were no significant differences in access to HCT for children noted based on sex or race. The lack of differential access to HCT for children compared with adults may be attributed, in part, to better governmental (including state gap programs) and private insurance for children compared with adults. In addition, a larger percentage of children, particularly those with acute leukemia, are referred early in their treatment course to larger pediatric medical centers and are treated on cooperative group trials, which may be more likely to afford them access to HCT.

Limitations

Several limitations of the current study should be considered. This analysis takes a national perspective in considering racial disparities in HCT. The CIBMTR collected data on approximately 55% of all autologous transplants and 50% of related donor transplants performed annually in the United States during the time period included in the current study. Although regional differences may be of greater interest because referral for HCT generally occurs on a local/regional basis, the nature of the SEER and CIBMTR databases preclude subanalyses to present regional differences in HCT. It is also possible that centers that perform more related donor or autologous HCTs in African American individuals are under-represented in the CIBMTR. We addressed this incomplete denominator of transplant activity in the United States by performing sensitivity analysis, the results of which suggested that our conclusions were robust up to a moderate (20%) level of under-reporting for specific racial groups. Because the CIBMTR captures data regarding nearly all unrelated donor transplants in the United States, potential biases in reporting are not an issue for that type of HCT and, in fact, disparities in utilization were found to be highest for unrelated donor HCT.

An additional consideration is that attribution of patient race in the CIBMTR observational database is provided by the transplant centers. Centers may not use homogenous processes to identify and report the race of HCT recipients; these designations may not match self-reported race and may contribute to reporting bias. However, it appears likely that reporting of race within the SEER database during the same time period would be subject to very similar biases, given the similarities in reporting methods between the 2 databases. If individuals from a particular race were systematically misclassified in any of these databases, it may misrepresent the true access rate for that particular race.

We assumed that family size, and therefore the number of potential sibling donors, was equal between African-American and Caucasian populations. Because the CIBMTR only collects data regarding HCT recipients, we were unable to explore whether differences exist between sex and racial groups with regard to rates of referral for consideration of HCT. Biologic-based racial differences in clinical presentation or response to initial therapy for disease may represent a partial explanation for the disparity in HCT rates. Unfortunately, we did not have sufficient data regarding disease status at the time of diagnosis or comorbidities to determine whether this may have affected consideration of HCT as a treatment option. Although for the purposes of these analyses we have assumed that the clinical appropriateness of HCT is similar across the groups studied as described above, other studies have suggested that African Americans are more likely to be diagnosed with an advanced stage of disease than whites, which would make them more likely to be candidates for aggressive therapy.32-34 However, if true, such differences in stage at diagnosis should serve to increase, not decrease, the ORs of HCT being performed among African Americans compared with Caucasians.

To the best of our knowledge, no data are currently available regarding patient preferences for treatment, rates of refusal of HCT, or other sociocultural factors that could explain the differences in HCT observed in the current study. Finally, there were insufficient data regarding healthcare process factors such as referring provider and transplant physician characteristics and practice patterns, geographic referral patterns, transplant center characteristics, or socioeconomic characteristics of the patient to be incorporated into these analyses.

Conclusions

We observed a difference in the utilization of HCT for leukemia, lymphoma, and MM by race, with Caucasians more likely to receive HCT than African Americans. Importantly, lower HCT rates for African Americans were noted for autologous HCT, indicating that donor availability cannot fully explain the differences observed. Differences by sex were less striking. We believe these differences represent substantial underutilization of HCT in African Americans. The identification of disparities should serve as the motivation to further understand their cause, and their elimination whenever they are inappropriate. Further study is essential to better characterize and explain disparities in access to HCT. Research should explore whether patient or provider preferences, sociocultural or socioeconomic factors, or healthcare process factors explain disparities in access to HCT, and whether these factors are modifiable. While waiting for further research to better understand disparate access to HCT, the medical community should work at all levels to eliminate these disparities.

CONFLICT OF INTEREST DISCLOSURES

The Center for International Blood and Marrow Transplant Research (CIBMTR) is supported by Public Health Service Grant/Cooperative Agreement U24-CA76518 from the National Cancer Institute (NCI); the National Heart, Lung and Blood Institute (NHLBI); and the National Institute of Allergy and Infectious Diseases (NIAID); a Grant/Cooperative Agreement 5U01HL069294 from NHLBI and NCI; contract HHSH234200637015C with the Health Resources and Services Administration (HRSA/DHHS); and 2 grants (N00014-06-1-0704 and N00014-08-1-0058) from the Office of Naval Research, as well as grants from AABB; Aetna; American Society for Blood and Marrow Transplantation; Amgen, Inc; an anonymous donation to the Medical College of Wisconsin; Astellas Pharma US, Inc; Baxter International, Inc; Bayer HealthCare Pharmaceuticals; Be the Match Foundation; Biogen IDEC; BioMarin Pharmaceutical, Inc; Biovitrum AB; BloodCenter of Wisconsin; Blue Cross and Blue Shield Association; Bone Marrow Foundation; Canadian Blood and Marrow Transplant Group; CaridianBCT; Celgene Corporation; CellGenix, GmbH; Centers for Disease Control and Prevention; Children's Leukemia Research Association; ClinImmune Labs; CTI Clinical Trial and Consulting Services; Cubist Pharmaceuticals; Cylex Inc; CytoTherm; DOR BioPharma, Inc; Dynal Biotech, an Invitrogen Company; Eisai, Inc; Enzon Pharmaceuticals, Inc; European Group for Blood and Marrow Transplantation; Gamida Cell, Ltd; GE Healthcare; Genentech, Inc; Genzyme Corporation; Histogenetics, Inc; HKS Medical Information Systems; Hospira, Inc; Infectious Diseases Society of America; Kiadis Pharma; Kirin Brewery Co., Ltd; The Leukemia and Lymphoma Society; Merck & Company; The Medical College of Wisconsin; MGI Pharma, Inc; Michigan Community Blood Centers; Millennium Pharmaceuticals, Inc; Miller Pharmacal Group; Milliman USA, Inc; Miltenyi Biotec, Inc; National Marrow Donor Program; Nature Publishing Group; New York Blood Center; Novartis Oncology; Oncology Nursing Society; Osiris Therapeutics, Inc; Otsuka America Pharmaceutical, Inc; Pall Life Sciences; Pfizer Inc; Saladax Biomedical, Inc; Schering Corporation; Society for Healthcare Epidemiology of America; StemCyte, Inc; StemSoft Software, Inc; Sysmex America, Inc; Teva Pharmaceutical Industries; THERAKOS, Inc; Thermogenesis Corporation; Vidacare Corporation; Vion Pharmaceuticals, Inc; ViraCor Laboratories; ViroPharma, Inc; and Wellpoint, Inc. The views expressed in this article do not reflect the official policy or position of the National Institute of Health, the Department of the Navy, the Department of Defense, or any other agency of the US Government.