Elsevier

Cancer Epidemiology

Volume 39, Issue 1, February 2015, Pages 8-13
Cancer Epidemiology

Racial differences in three major NHL subtypes: Descriptive epidemiology

https://doi.org/10.1016/j.canep.2014.12.001Get rights and content

Highlights

  • The three largest NHL subtypes are DLBCL, FL, and CLL/SLL.

  • There are racial differences in terms of patients’ characteristics, incidence, and survival, and the patterns vary across subtypes.

  • Plausible interpretations for the observed across-race and across-subtype differences are provided.

  • More data collection and analysis are needed to more comprehensively describe and interpret the differences.

Abstract

Background

NHL (non-Hodgkin lymphoma) consists of over 60 subtypes, ranging from slow-growing to very aggressive. The three largest subtypes are DLBCL (diffuse large B-cell lymphoma), FL (follicular lymphoma), and CLL/SLL (chronic lymphocytic leukemia/small lymphocytic lymphoma). For each subtype, different racial groups have different presentations, etiologies, and prognosis patterns.

Methods

SEER (Surveillance, Epidemiology, and End Results) data on DLBCL, FL, and CLL/SLL patients diagnosed between 1992 and 2010 were analyzed. Racial groups studied included NHW (non-Hispanic whites), HW (Hispanic whites), blacks, and API (Asians and Pacific Islanders). Patient characteristics, age-adjusted incidence rate, and survival were compared across races. Stratification and multivariate analysis were conducted.

Results

There are significant racial differences for patients’ characteristics, including gender, age at diagnosis, stage, lymph site, and age, and the patterns vary across subtypes. NHWs have the highest incidence rates for all three subtypes, followed by HWs (DLBCL and FL) and blacks (CLL/SLL). The dependence of the incidence rate on age and gender varies across subtypes. For all three subtypes, NHWs have the highest five-year relative survival rates, followed by HWs. When stratified by stage, racial difference is significant in multiple multivariate Cox regression analyses.

Conclusions

Racial differences exist among DLBCL, FL, and CLL/SLL patients in the U.S. in terms of characteristics, incidence, and survival. The patterns vary across subtypes. More data collection and analysis are needed to more comprehensively describe and interpret the across-race and subtype differences.

Introduction

Non-Hodgkin lymphoma (NHL) is a heterogeneous group of lymphoproliferative malignancies. In recent years, the incidence rate of NHL in American men and women has been the highest in the world [1]. It is the fifth-most-common cancer in both men and women in the U.S., with an estimated 70,800 new cases and 18,990 deaths in 2014 [2]. NHL has over 60 subtypes. DLBCL (diffuse large B-cell lymphoma), the most common subtype, is an aggressive cancer of the B cells and comprises approximately 30% of all cases. FL (follicular lymphoma), the second-most-common subtype, is generally indolent. It is a lymphoma of the follicle center B cells, which has at least a partially follicular pattern. CLL (chronic lymphocytic leukemia) is a stage of SLL (small lymphocytic lymphoma), a type of B-cell lymphoma. They are considered to be the same underlying disease with different appearances. They were merged into an aggregate category by the 2001 WHO (World Health Organization) classification scheme and are the third-most-common subtype of NHL. There are also a large number of smaller subtypes [3]. Some studies have analyzed NHL overall, while with the significant heterogeneity across subtypes, others have conducted subtype-specific analyses. For NHL overall and the multiple subtypes, race has been identified as an important risk factor in multiple aspects [4], [5].

The goal of this study is to systematically describe the racial differences for DLBCL, FL, and CLL/SLL patients in the U.S. Those are the three largest subtypes and are all B-cell lymphomas, which account for about 85% of NHL [6]. Racial differences have been studied for multiple cancer types, including NHL overall and individual subtypes [7], [8], [9], [10], [11]. However, the existing studies may be limited by focusing on a specific subtype (for example, some studies [8] focus on DLBCL only), a narrow spectrum of racial groups (for example, Koshiol et al. [12] only compared whites and blacks), or specific outcomes (for example, treatment and survival [8]). In this study, we conducted a unified analysis of racial differences for the three largest NHL subtypes using the SEER database and applying the same analysis approach. The analysis results were expected to be more comparable across subtypes than those in the literature, which are based on different databases using different analysis methods. They can reveal the similarity or dissimilarity in racial difference patterns across subtypes. In addition, for each subtype, this study aims to be more comprehensive by comparing a wider spectrum of racial groups, including NHW (non-Hispanic whites), HW (Hispanic whites), blacks, and API (Asians and Pacific Islanders), and by analyzing multiple aspects, including patients’ characteristics, clinical-pathological features, incidence rate, and survival rates. Analyzing and comparing multiple cancer types and subtypes can provide critical clues for future epidemiological investigation and more insights than single-(sub)type analysis [13], [14].

Section snippets

Source population

The population-based sample was obtained from the SEER (Surveillance, Epidemiology, and End Results, http://seer.cancer.gov/) database. The SEER 9, 13, and 18 registries were analyzed in this study and cover approximately 9.5%, 14%, and 28% of the U.S. population, respectively. For each case, the first matching record was selected for analysis. Patients with DLBCL, FL, and CLL/SLL were identified and categorized using ICD-O-3 (International Classification of Diseases for Oncology, Third Edition

Patients’ characteristics and clinical-pathological features

Results are presented in Table 1. Only DLBCL had a significant racial difference in gender distribution (P < 0.0001), with blacks having the highest percentage of males (58.31%) and APIs having the lowest (52.92%). All three subtypes exhibit significant racial differences in the distribution of age at diagnosis. The pattern is consistent across subtypes, with NHWs having the highest age at diagnosis, followed by APIs and then HWs. Overall, CLL/SLLs have a higher age at diagnosis. For all three

Discussion

Epidemiologic studies on NHL have been conducted extensively. Most of the existing studies have focused on homogeneous samples. However, multiple studies [17], [18], [19], [20], [21] have indicated that the characteristics, incidence rates, and survival rates of certain racial groups are different from others. Examples include observations made on the European population [17], the Koreans [18], the Lebanese [20], the Polish population [21], and others. A limitation shared by some of the

Funding

This work was supported by Yale Comprehensive Cancer Center (P30 CA16359 from NIH) and the National Natural Science Foundation of China under grant no. 71301162. The funders had no role in study design, data collection and analysis, or manuscript preparation.

Conflicts of interest

None.

Authorship contribution

SM designed the study. YL, YW, and ZW conducted data analysis. All authors were involved in writing and approved the final draft.

Acknowledgements

We thank the editor and reviewers for careful review and insightful comments, which have led to a significant improvement of the article.

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    These authors contributed equally to this work.

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