Frequency of acute myeloid leukemia in children attended in Belém , Pará from August 2005 to May 2009 Frequência de leucemia mieloide aguda em crianças atendidas em Belém , Pará , no período de agosto de 2005 a maio de 2009

1. Faculdade de Medicina de Ribeirão Preto – Universidade de São Paulo (USP); Laboratório de Patologia Geral-Imunopatologia e Citologia da Universidade Federal do Pará (UFPA); Fundação Pública Estadual Hospital de Clínicas Gaspar Vianna. 2. UFPA. 3. Fundação Centro de Hemoterapia e Hematologia do Pará (HEMOPA). 4. UFPA; Hospital Ophir Loyola. 5. Universidade Federal de São Paulo (UNIFESP); Hospital Ophir Loyola. 6. Universidade do Estado do Pará (UEPA); Fundação Pública Estadual Hospital de Clínicas Gaspar Vianna.

AML incidence in children aged 0-14 years in the United States, in 2005-2009, in turn, was estimated at 7.7 cases per million children.With little variation between racial/ethnic groups in the US, except for a possible increase in the incidence rate in Hawaiian, residents of the Pacific Islands and Hispanic-Latino children, is a fact that in general could suggest shared genetic predisposition among these groups (5,7,20) .
In Brazil, there are still few existing data on the incidence of AML in pediatric patients (16,17,19,21,22) , when compared with acute 10.5935/1676-2444.20150013lymphocytic leukemia (ALL) (10,14,22,23) .According to estimates from the Brazilian National Cancer Institute (Instituto Nacional do Câncer [INCA]) for leukemias in general in 2014 in Brazil, new cases rate from 5.20 in men and 4.24 in women per 100,000 patients.When this analysis was performed in relation to Northern Brazil, INCA estimates for new cases of leukemia in 2014 were 3.57 in men and 2.81 in women per 100,000 patients (30) .This situation is even more precarious when the incidence of pediatric AML is at issue in the Amazonian area, due to underreporting of cases.
Among the unique characteristics of the Northern region of Brazil, possibly associated with the AML incidence, we highlight the exposure to carcinogens derivatives of: (1)   The study included 278 patients diagnosed with AML or chronic myeloid leukemia (CML), of both genders and aged between 10 months and 78 years.AML was confirmed for 70/278 (25.18%) of these, and 37/70 were in pediatric age (0-17 years).Among the epidemiological data were analyzed gender, age, main clinical complaints, and relevant laboratory results on blood cells count and myelogram.

Statistical analysis
Data were grouped according to age and gender information of patients diagnosed with AML in children attended during this period.They were stored and analyzed using software BIOESTAT 5.0 (Aires et al., 2007), applying the chi-square test, with p < 0.05.

RESuLtS
In the chosen period from the 278 cases studied, 70 (25.2%)patients had clinical, morphological and immunophenotypic AML diagnosis confirmed; the remaining patients were diagnosed as follows: 146 (52.5%) with ALL, and 62 (22.3%) with chronic lymphoproliferative syndromes.
Regarding the age distribution of all AML (70/278) cases, we observed that the pediatric age group aged 0-10 years (28/70 cases) showed the highest number (40%) of individuals (Table 1), with a median age of 7 years and 8 months.
Regarding the study of the pediatric population, in accordance with the Brazillian Ministry of Health (Ministério da Saúde), which considers the age between 0 and 17 years, 37/70 (52.9%) individuals with AML.Thus three cases of patients aged 11-20 years were excluded (3/15) (Table 1), because they have reached the age of 19 years.
The male (19/37) and female (18/37) distribution analysis in the pediatric population of this study showed no statistical difference (p = 0.752).

DiSCuSSion
The laboratory advances in the diagnosis of AML, based primarily on the development of monoclonal antibodies on cytogenetic, molecular biology, and flow cytometry techniques, have increased not only the accuracy in the definition of myeloid lineage as well as in the classification of AML subtypes (14,15,21,22) .However, today, in many Brazilian states of the northern region, AML diagnosis and epidemiology are still quite precarious, due to the distances to be covered between the places of origin of the patients and the diagnostic centers, and due to financial difficulties for this displacement or even the low reporting of positive cases who die even before the definitive diagnosis and treatment.
Given these facts, this study sought to identify the frequency of AML, its subtypes and most relevant clinical, morphological and immunophenotypic findings, observed among patients who were able to overcome the initial difficulties and get to the main diagnostic and treatment centers for this type of pathology between 2005 and 2009.
The interest in the AML stratification in children, in turn, appeared due to the demand on identification of frequency of this disease in pediatric groups in Belém, especially because AML, in pediatric oncology, an entity, together with neuroblastoma and central nervous system tumors, is one of the three most frustrating conditions in relation to patients survival (5,17) .Borato et al. (16) and Zanichelli et al. (15) point out in their study that the greatest challenges in the treatment of AML in children is to reduce the mortality rate in the initial phase of treatment (remission induction), with consequent reduction of infectious and hemorrhagic complications and ensuring adequate hospital support, compromised by the high treatment costs.
In our study, about 85% to 90% of attended patients belonged to the Brazilian Unified Health System (Sistema Único de Saúde [SUS]), without major financial resources to stay away from home, and usually tin a more advanced stage of the disease, showing therefore, the importance of knowing the frequency of this disease among patients seeking expert healthcare.This process allows the exchange of successful experiences with other Brazilian diagnostic and treatment centers, besides State financial planning and prospects for implementing a hematopoietic stem cell transplant (HSCT) center, to attend the region.
The results of this study with children aged 0-17 years showed similarities with the studies of Zanichelli et al. (15) , Viana et al. (19) , Emerenciano et al. (6) , who also observed higher frequencies of AML M2 and AML M0/M1 subtypes in children.
The lower overall frequency in adults and children with AML M3 observed in our study, although different from the Brazilian literature  in general (3,22) , corroborates other studies with specific population in the States of Piauí (7,8%) (18) and Amazonas (13%) (23) , possibly due to population characteristics and similar ethnic composition.
Supporting this aims, general studies have tried to show the association between HLA risk variants for some types of leukemia and miscegenation of the Brazilian population (1) , such as the associations observed by Barion et al. (16) of the relationship between HLA B53 and HLA-B56 with ALL; HLA-B7 with AML; and HLA-A24, HLA-B45, HLA-DRB1*04 and DRB1*08 with CML, although further studies on the subject in Brazil are still necessary.
Extrinsic etiological factors have also been associated with AML, such as exposure to ionizing or non-ionozantes radiation, organophosphates, benzene, ethylene oxide, antineoplastic agents, chlorinated pesticides (chlordane and heptachlor), among other myelotoxic and carcinogenic agents (25)(26)(27)(28)(29) .Among these, in the Amazon region, the extrinsic etiologic factors most likely to be associated with increased incidence of pediatric are the organophosphates (insecticides and herbicides), methylmercury and chlorinated pesticides associated with food contamination (28,29) , since this is a region of great agricultural expansion and gold exploration, where the use of these products are quite common.These organophosphate and chlorinated pesticides, however, beyond what has already been mentioned, are also present in the construction and maintenance of roads, the treatment of wood for construction, storage of grains and seeds, the production of flowers, to combat endemics and epidemics, and domestic use (detergents, waxes, disinfectants, insecticides, soap powders, among others) (28) .
As regards the clinical and laboratory data observations most commonly noticed at the time of AML diagnosis, our data were concordant with those described in the literature (2,4,8,12,25) .
We also did not observe in this study, significant differences in the distribution of AML subtypes in children when the analysis period was from 2009 to October 2013 (data not shown).

PatientsA
retrospective study of medical records of patients with AML diagnosis based on clinical and morphological criteria (FAB/OMS), and immunophenotypic profile of blasts by flow cytometry, from August 2005 to May 2009, to determine the frequency of AML subtypes in children aged 0-17 years, treated at Belém, Pará.A Commitment Term for Restricted and Confidential Use of Database was settled and signed by the research coordinator regarding the project which originated this article.

Frequency
of acute myeloid leukemia in children attended in Belém, Pará from August 2005 to May 2009

taBLE 2 -
AML subtypes in children aged 0 to 17 years