Distribution of Lymphomas in Mexico: A Descriptive Study

Introduction

Lymphomas are a heterogeneous group of hematological malignancies of which incidence, prevalence, and epidemiological factors are still not well described in the Mexican population. Most of the recent descriptive studies do not specify details of their analysis and were not based on the WHO classification of tumours. In our study we analyzed 5772 lymphomas diagnosed over a period of 10 years between 2005 and 2014, and classified them according to the 2008 WHO Classification of Tumours of Lymphoid Tissues. The aim of our study is to determine frequencies and subtypes of the main non-Hodgkin's and Hodgkin's lymphomas in a heterogeneous sample of biopsies in the Mexican population.

Methods

Files for tissue samples for lymphomas stored in 5 different hospitals in Mexico City were retrieved for re-analysis. All cases where tissue samples were available were stained with hematoxylin and eosin as well as immunostained. Analysis was performed to differentiate the main mature B-cell, T-cell, Hodgkin's, and precursor lymphoid neoplasms according to the 2008 WHO classification of tumours. Age and sex were obtained and registered from the original submitted request for pathology assessment. All stains were performed in the same laboratory and interpreted by 3 pathologists who provided a diagnosis.

Results

5772 neoplasms were included in this study. Of these, 4213 were mature B-cell neoplasms (73%; 95%CI 71.83 - 74.12), 888 Hodgkin's lymphomas (HL) (15%; 95%CI 14.48 - 16.34), 496 mature T-cell / NK neoplasms (9%; 95%CI 7.89 - 9.34), and 175 precursor lymphoid neoplasms (3%; 95%CI 2.62 - 3.5). Neoplasms had an even distribution between sexes, with 51% of the cases being male patients.

All 4 different categories of neoplasms were further analysed and classified. Six main mature B-cell lymphomas accounted for almost 95% of our cohort. These included diffuse large B-cell lymphoma (DLBCL) (56%; 95%CI 54.39 - 57.39), follicular lymphoma (FL) (20%; 95%CI 18.92 - 21.34), mantle cell lymphoma (6.7%; 95%CI 6.02 - 7.53), marginal zone/MALT lymphoma (5.2%; 95%CI 4.59 - 5.93), chronic lymphocytic leukemia/small lymphocytic lymphoma (4.6%; 95%CI 4.01 - 5.28), and Burkitt's lymphoma (2.5%; 95%CI 2.04 - 2.98). Hodgkin's lymphomas were also classified in 6 main subtypes, with nodular sclerosis (47%; 95%CI 44.14 - 50.7) and mixed cellularity (38%; 95%CI 34.49 - 40.85) being the most common. Several mature T-cell / NK neoplasms were identified, with the majority of cases being peripheral T-cell lymphoma NOS / anaplastic large cell lymphoma ALK negative (44%; 95%CI 39.85 - 48.84) and extranodal NK/T-cell lymphoma, nasal type (30%; 95%CI 25.5 - 33.76). Please refer to Table 1, 2, and 3 for further information.

Analysis of cases by group age was also performed for mature B-cell neoplasms and HL. As expected, the majority of cases of DLBCL were seen in the age groups of 41-60 as well as 61-80. The same applied to FL. In the case of HL, the majority of nodular sclerosis subtypes were seen in the group age of 21-40 and mixed cellularity subtype showed a more even distribution in the age groups between 21-80.

Conclusion

To our knowledge, this is the first descriptive study with a large sample of confirmed lymphoid neoplasms, using a standardized method of staining, classified according to the 2008 WHO Classification of Tumors representative of the Mexican population. It is a complement to the current epidemiologic registry of neoplasms in Mexico, adding classification details according to global standards set by the WHO. The results obtained are in keeping with the numbers described in other population studies worldwide.

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