INTRODUCTION
Acute lymphoblastic leukemia (ALL) represents the most common childhood
malignancy, accounting for approximately 28 % of cancers and 80 % of
all leukemias in children 1,2. ALL presentation is
bimodal, with the first peak occurring in childhood, and a second peak
around age fifty 1. Its incidence is reported to be
higher in Hispanic children at 43 cases per million vs. 28 in
non‐Hispanics 3 and in Mexico it has been reported at
49.5 cases per million.4
The pathogenesis of ALL is complex and remains elusive, exogenous and/or
endogenous exposures, genetic susceptibility, biologic heterogeneity,
and chance appear to have roles 5,6. Environmental
risk factors including infections are an area of particular interest in
leukemia’s etiology 7,8 and epidemiological
investigation into the periodicity of leukemia onset, which has a long
history, and the evidence for seasonal variation in incidence may
provide insight into this hypothesis9,10. Many viral infections have
characteristic seasonal onsets, thus investigations had suggested that
ALL is related to infection or other seasonally-varying environmental
risk factors 11–13.
Seasonal variation in diagnosis of children with ALL may provide
evidence of an infectious etiology for childhood ALL, as seasonal
climatic changes give rise to respiratory infections or gastrointestinal
infections in winter, spring, and summer. This might possibly suggest
the presence of environmental factors such as pesticides, which are
applied frequently in rural areas. Also, spatiotemporal clusters occur,
with an excess of childhood ALL cases observed in a determined
geographical area at certain points in time compared with other areas
and other times.14 Importantly, most studies reporting
seasonal trends do so in countries with temperate-cool climates15, with a few conducted in arid or semiarid regions,
which have a rather short winter season 16.
Studies addressing the seasonality of presentation in acute leukemia
report contrasting results 17–20. Time trends and
seasonal variations have been assessed, while some have not identified a
seasonal pattern 20,21 , others have found significant
seasonal influence 17,19,22. Most studies on this
subject have analyzed different reference dates, including birth date,
first symptom date or diagnosis date, and used different statistical
methods, leading to inconsistencies and controversy in the results. The
evidence obtained may contribute to learn about potential seasonally
varying environmental risk factors, such as infections or pesticide
exposure, especially in Latin America where this pattern is less clear,
with few reports documenting this aspect of childhood and adolescence
ALL.
The present study aimed to investigate the presence of seasonal
variation in month of diagnosis in a homogeneous ethnic and
socioeconomic group of Hispanic children and adolescents with ALL in a
low-middle income population over a 15-year period.