Leukaemia is the most common cancer in children. Its incidence is about 4 in 100,000 children. In Hong Kong, some 50 to 60 children are diagnosed to suffer from leukaemia every year.
The cause of leukaemia in most patients is unknown but it may occasionally be related to excessive irradiation such as in areas of nuclear activity, oncogenic viruses or chemical exposure. Children with Down syndrome also have a higher chance of developing leukaemia.
The common types of leukaemia are:
(1) Acute lymphoblastic leukaemia (ALL): accounting for about 80% of all leukaemia cases.
(2) Acute non-lymphoblastic leukaemia (ANLL) or acute myeloid leukaemia (AML): about 15% of all leukaemia cases.
(3) Chronic myeloid leukaemia (CML): about 5% of all leukaemia cases.
In leukaemia, the white blood cells have turned malignant. They multiply incessantly in the bone marrow, thus affecting the function of normal bone marrow; at the same time, the cancer cells spread to other parts of body through the bloodstream.
The common symptoms of leukaemia are:
Easy bruising, gum and nose bleeding
Enlargement of lymph glands
Bone and joint pain
Abdominal pain and discomfort
Poor appetite, weight loss
The basic diagnostic tests include:
Blood cell counts: Blood will be drawn from the vein of the patient to examine the abnormal blood cell.
Bone marrow examination: The child is first put to sleep with a sedative and local anaesthetics will be injected. The doctor will then use a syringe to aspirate a small amount of bone marrow from the pelvic bone. The diagnosis is leukaemia if there is a large number of cancerous white cells in the bone marrow.
Cerebrospinal fluid test: A lumbar puncture will be performed to examine if the leukaemia cells have spread to the central nervous system.
X-ray: e.g. chest X-ray.
Electrolytes, uric acid, renal function and liver function tests.
Treatment of leukaemia is mainly by chemotherapy. The most appropriate regimen will be chosen according to the leukaemia type. Different protocols of chemotherapy are used according to the characteristics of the cancerous white cells.
For treatment of acute lymphoblastic leukaemia (ALL), the doctor will prescribe a combination of anti-cancer drugs which are taken orally and by injection. In addition to chemotherapy, some children may also require radiotherapy to the head. The entire treatment will last 2 to 3 years.
The relapse rate of acute non-lymphoblastic or myeloid leukaemia (AML) with chemotherapy is high. Hence, if the child has siblings whose HLA (antigens on the surface of white cells) are identical with his, treatment by bone marrow transplantation will give a better chance of cure.
Similarly, bone marrow transplantation for children with chronic myeloid leukaemia(CML) offers a greater chance of cure. Currently, studies are being carried out on the long term disease control by interferon injections.
The chance of cure for acute lymphoblastic leukaemia (ALL) by chemotherapy is about 60-70%. The chance of cure for acute non-lymphoblastic leukaemia (ANLL) or acute myeloid leukaemia (AML) is about 20-30%. The chance of cure for chronic myeloid leukaemia (CML) by bone marrow transplantation is about 60%.