Cancer describes all diseases characterized by the abnormal production of a certain type of cell within the organism. These cells have a much higher speed of growth and division than normal cells, which means that they gradually invade the body.

Leukemia is the uncontrolled proliferation of an abnormal population of cells in the blood. These abnormal cells infiltrate the bone marrow, impeding the production of the remaining normal cells, and invading the blood and other organs.

Leukemia is the most common cancer in children and teens, accounting for almost 1 out of 3 cancers. Overall, however, childhood leukemia is a rare disease. About 3 out of 4 leukemias among children and teens are acute lymphoblastic leukemia (ALL). Most of the remaining cases are acute myeloid leukemia (AML).

The incidence, biology, and outcome of childhood acute leukemia vary according to age, gender, and ethnicity. In many high-income countries, the incidence of pediatric ALL is rising by an average of about 1% every year.

The incidence in Latin American countries is higher than that of Europe. However, the outcome is worse than in Europe. This could be influenced by biological factors like the genetic background, the geographic environment, the access and compliance to treatment, the healthcare models, cultural, socio-economic, lifestyle and behavioral factors, and the lack of resources and infrastructures that limit the research in these regions.

The outcome of childhood leukemia has dramatically improved in the past few decades, largely as a result of improvements in risk stratification and therapeutic protocols led by international cooperative groups.

The 5-year survival rate for children is about ~80% for acute lymphoblastic leukemia (ALL) and ~60% for acute myeloid leukemia (AML). In general, children in lower-risk groups have a better outcome than those in higher-risk groups. But it is important to know that even children in higher-risk groups can often be cured.

The population-based data from huge epidemiological studies such as CONCORD, gathering nearly 90.000 children with acute leukemia from 64 countries, stated worldwide differences in outcome according to regions: the best outcomes were observed in North America, Oceania and some European countries, with survival higher than 90%, in contrast to the heterogeneous survival reported in Central and South American countries, ranging from 52% to 85%.

Current treatment protocols are intensive, typically involving multiple chemotherapeutic drugs administered over several months or years. Stem cell transplantation is reserved for high-risk patients.

Different International Cooperative Groups have for decades led the study and treatment of childhood leukemia, designing consecutive clinical trials, in which the new knowledge and technological developments were progressively applied.

Patients may present fatigue, pallor and weakness, bone pain, anemia, infections, fever, bleeding or bruising. During the physical exam, the doctor will probably focus on any enlarged lymph nodes, areas of bleeding or bruising, or possible signs of infection. The eyes, mouth, and skin will be looked at carefully, and a thorough nervous system exam may be done. Spleen or liver enlargement will be discarded.

Certain signs and symptoms can suggest that a person might have leukemia, but some tests are needed to confirm the diagnosis.

The thorough biological diagnosis of the different subtypes of acute leukemia may be complex and expensive. The presence of determined genetic abnormalities, along with other clinical variables like age, white blood cell count and lineage define in most therapeutic protocols the risk stratification of patients with childhood leukemia at diagnosis.

In the last decade, more complex technologies have been introduced, allowing to partially elucidating the complex biology of leukemias.

CLOSER is a collaborative, international and multidisciplinary initiative to study childhood leukemias. CLOSER’s consortium includes experts in diagnosis, in clinical care and treatment, in research, in training, in innovation and in defending patients’ rights and interests.

To improve the biological diagnosis of childhood leukemia, refine the risk-stratification of patients and help to harmonize the outcome of children with acute leukemia between Europe and Latin America.

Cancer is becoming one of the most important public health problems worldwide.

Current cancer care does not fully reflect ethnic, cultural, environmental and resource differences. Besides, limited research is being conducted on tumors primarily found in Latin American countries.

There is a need to establish evidence obtained through international high-quality translational collaborative research to tailor cancer control to specific patient groups.

CLOSER project approaches childhood leukemia care in a global and innovative manner, focusing on scientific aspects, but also on socioeconomic, cultural, educational and environmental factors, to improve the survival rate and quality of life of children with leukemia, their families and their caregivers.