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  ..Reasons and factors of risk
The application of the molecular biology techniques to the domains of the leukemias improves the understanding of these illnesses. The recent works are interested in the precocious, molecular events, responsible of the leucémogenèse. From now on, these techniques improve the identification of the illness while permitting the definition of transcribes fusion and the description of the rearrangements between the genes of the immunoglobines or the T. receptors
The contributions of these techniques are of two orders:Â better knowledge on the molecular definition of the illness and possibility of a follow-up of the vestigial illness. One must signal the interest of the techniques of in vitro tests of the anti-leukemic activity of the different medicines. Few works exist on the physiology of the leukemic cells, with the exception of study of the angio-genetic factors,
 ..The signs of the illness
The clinical signs translate either the medullary insufficiency is the visceral infiltration by the abnormal cells. The medullary insufficiency drags:
   * A decrease of the red globules therefore an anemia: paleness, asthénie, thinning, change of the general state;    * A decrease of the leukocytes therefore a fragility opposite the infections: trailing anginas, unexplained fever...    * A decrease of the tablets therefore a thrombopénie: hemorrhages, épistaxis, pétéchies, purpura, bruises etc... The hemorrhages visible rétiniennes to the bottom of eye is annonciatrices of hemorrhages cérébro-méningées.
 ..The infiltration of the organs by the leukemic cells provokes:
   * An increase of the volume of the liver and/or the spleen;    * An increase of volume of the lymph nodes;    * Of the bony or ostéo-articular pains;     * Of the abdominal pains;    * A hypertrophy hémorragique of the gums (gingivitis)
 ..To the least doubt, the physician calls on the laboratory.
The NFS gives two types of renseignements.Pratiquée precociously, to the stage "aleucémique", the cancerous cells didn't appear again in the blood circulation. The analysis of blood doesn't show them therefore. On the other hand, the medullary insufficiency is translated by:
   * The fall of the number of the hématies: anemia normochrome arégénérative;    * The fall of the number of the leukocytes: neutropénie;    * The fall of the number of tablets: thrombopénie.
Later, she puts in evidence the abnormal young cells (blastes) that passed in the circulation. These results impose to practice a puncture of marrow in order to achieve a smear or myélogramme.
 ..One distinguishes two main shapes indeed:
   * The leukemias sharp lymphoblastiques or L.A.L., the most frequent between 18 months and 16 years, very sensitive to the modern treatments since the complete remissions are reached in 90% of the cases during many months.    * The leukemias sharp myéloblastiques or L.A.M. concerning especially the children of more than 12 years and more serious
 ..Complications
Before the modern treatments, the children affected by leukemia died quickly. Currently, the therapeutic various clarifications these last years permit to get remissions of length more or less long. One speaks of complete recovery when a remission lasts 5 years. A "remission" defines itself by the disappearance of the clinical and hematological signs with resurgence of the normal medullary lineages in marrow. Several complications can occur:
   * The medullary aplasie is provoked by the treatment that takes care of the leukemia in a way but drags the serious infections or the stern hemorrhages.    * The different treatments have an effect immunodépresseur and make very sensitive the children to the viral infections (chickenpox, measles etc...)   * the localized leukemic infiltrations can reach the brains (leukemic meningitis). This relapses méningées was responsible for the precocious hematological relapses during the first year of treatment. A preventive treatment is done currently systematically. The testicular attacks are relatively frequent and impose the regular exam of the external genitalia (progressive and painless increase of the volume of a testicle).
When the illness doesn't answer the maintenance treatments or réinduction anymore, the evolution makes itself the most often toward the death by medullary aplasie.
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