Lindsay M. Morton

Because the causes of most lymphoid neoplasms remain unknown, comparison of incidence patterns by disease subtype may provide critical clues for future etiologic investigations. We therefore conducted a comprehensive assessment of 114,548 lymphoid neoplasms diagnosed during 1992-2001 in 12 Surveillance, Epidemiology, and End Results (SEER) registries according to the internationally recognized World Health Organization (WHO) lymphoma classification introduced in 2001. Cases coded in International Classification of Diseases for Oncology, Second Edition (ICD-O-2), were converted to ICD-O-3 for WHO subtype assignment. Age-specific and age-adjusted rates were compared by sex and race (white, black, Asian). Age-adjusted trends in incidence were estimated by sex and race using weighted least squares log-linear regression. Diverse incidence patterns and trends were observed by lymphoid neoplasm subtype and population. In the elderly (75 years or older), rates of diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma increased 1.4% and 1.8% per year, respectively, whereas rates of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) declined 2.1% per year. Although whites bear the highest incidence burden for most lymphoid neoplasm subtypes, most notably for hairy cell leukemia and follicular lymphoma, black predominance was observed for plasma cell and T-cell neoplasms. Asians have considerably lower rates than whites and blacks for CLL/SLL and Hodgkin lymphoma. We conclude that the striking differences in incidence patterns by histologic subtype strongly suggest that there is etiologic heterogeneity among lymphoid neoplasms and support the pursuit of epidemiologic analysis by subtype.

Collectively, lymphoid neoplasms are the fourth most common cancer and the sixth leading cause of cancer death in the United States. The authors provide contemporary lymphoid neoplasm statistics by subtype based on the 2008 World Health Organization classifications, including the most current US incidence and survival data. Presented for the first time are estimates of the total numbers of US lymphoid neoplasm cases by subtype as well as a detailed evaluation of incidence and survival statistics. In 2016, 136,960 new lymphoid neoplasms are expected. Overall lymphoma incidence rates have declined in recent years, but trends vary by subtype. Precursor lymphoid neoplasm incidence rates increased from 2001 to 2012, particularly for B-cell neoplasms. Among the mature lymphoid neoplasms, the fastest increase was for plasma cell neoplasms. Rates also increased for mantle cell lymphoma (males), marginal zone lymphoma, hairy cell leukemia, and mycosis fungoides. Like incidence, survival for both mature T-cell lymphomas and mature B-cell lymphomas varied by subtype and by race. Patients with peripheral T-cell lymphomas had among the worst 5-year relative survival (36%-56%, depending on race/sex), while those with mycosis fungoides had among the best survival (79%-92%). For B-cell lymphomas, 5-year survival ranged from 83% to 91% for patients with marginal zone lymphoma and from 78% to 92% for those with hairy cell leukemia; but the rates were as low as 47% to 63% for patients with Burkitt lymphoma and 44% to 48% for those with plasma cell neoplasms. In general, black men had the lowest survival across lymphoid malignancy subtypes. These contemporary incidence and survival statistics are useful for developing management strategies for these cancers and can offer clues regarding their etiology. CA Cancer J Clin 2016;66:443-459. © 2016 American Cancer Society.

Since 2001, the World Health Organization classification for hematopoietic and lymphoid neoplasms has provided a framework for defining acute leukemia (AL) subtypes, although few population-based studies have assessed incidence patterns and patient survival accordingly. We assessed AL incidence rates (IRs), IR ratios (IRRs), and relative survival in the United States (2001-2007) in one of the first population-based, comprehensive assessments. Most subtypes of acute myeloid leukemia (AML) and acute lymphoblastic leukemia/lymphoma (ALL/L) predominated among males, from twice higher incidence of T-cell ALL/L among males than among females (IRR = 2.20) to nearly equal IRs of acute promyelocytic leukemia (APL; IRR = 1.08). Compared with non-Hispanic whites, Hispanics had significantly higher incidence of B-cell ALL/L (IRR = 1.64) and APL (IRR = 1.28); blacks had lower IRs of nearly all AL subtypes. All ALL/L but only some AML subtypes were associated with a bimodal age pattern. Among AML subtypes, survival was highest for APL and AML with inv(16). B-cell ALL/L had more favorable survival than T-cell ALL/L among the young; the converse occurred at older ages. Limitations of cancer registry data must be acknowledged, but the distinct AL incidence and survival patterns based on the World Health Organization classification support biologic diversity that should facilitate etiologic discovery, prognostication, and treatment advances.

Self-selection bias may threaten the internal validity of epidemiologic studies. Studies with a low level of participation are particularly vulnerable to this bias, and commentators note apparent declines in participation in recent years. The authors therefore conducted a retrospective review to survey the practice of reporting participation in epidemiologic studies, to assess changes in participation over time, and to evaluate the impact of increased biologic specimen collection on participation. The authors abstracted selected study characteristics from 355 peer-reviewed, original, analytic-epidemiology research articles published from January 1 to April 30, 2003, in 10 high-impact general epidemiology, public health, and medical journals. At least some information regarding participation was provided in 59% of cross-sectional studies, 44% of case-control studies, and 32% of cohort studies. Participation appears to have declined during 1970-2003 for all study designs. Participation declined most steeply for controls in population-based, case-control studies (-1.86% per year, 95% confidence interval: -3.03, -0.69), with steeper declines after 1990. Proportionately more studies collected biologic specimens over time, particularly for cohort and case-control study designs (p(trend) = 0.06 and 0.03, respectively), yet participation was reported separately for the biologic specimen study component in only 27% of studies. The authors conclude that epidemiologists need to address declining participation and to report participation consistently, including for biologic specimen collection.