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12 October 2010

Leukaemia: your questions answered

Prof Vernon Louw answers frequently asked questions about leukaemia.

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1. What is leukaemia?

Leukaemia is a progressive cancer of the blood-forming organs, particularly the bone marrow, which is marked by the production of too many white blood cells. Other organs involved in cellular development such as mucosa of the digestive and respiratory tracts, lymph nodes, spleen and thymus can also be affected.

All blood cells, including red blood cells, platelets and normal white blood cells are produced in the bone marrow. In people with leukaemia, higher numbers of immature white blood cells displace the normal bone marrow cells, resulting in a decrease in the production of normal red and white blood cells as well as platelets.

2. What do the different types of blood cells do?

Red blood cells carry oxygen from the lungs to the organs of the body. Platelets are needed during the blood clotting process, while white blood cells fight off infections. All three blood cells are produced in the bone marrow. They then mature in the bone marrow until they become fully useful and functional in the body. 

In leukaemia, immature white blood cells prevent normal numbers of other blood cells from developing. The deficiency in red blood cells can lead to anaemia, and the shortage of platelets means people with leukaemia may bruise easily or bleed excessively. Normal white blood cells - which are involved in fighting illnesses - may be suppressed or dysfunctional and can render the patient’s immune system unable to fight off simple infection. 

Because leukaemia prevents the immune system from working normally, some patients experience frequent infections, ranging from infected tonsils, sores in the mouth, to diarrhoea and life-threatening pneumonia and opportunistic infections. 

3. What are the main types of leukaemia?

Leukaemia covers a broad spectrum of disorders, but there are two main types, namely acute and chronic. 

In acute leukaemias, the maturation process of cells is disrupted and immature cells, also known as blasts, flood the bone marrow. These cells are not yet fully useful. As they multiply rapidly, they displace healthy cells from the bone marrow, leading to a decrease in the production of other normal blood cells. Acute leukaemias develop rapidly and without treatment, patients can die within a matter of days or weeks. 

In chronic leukaemias, cancerous cells mature slightly more than in acute leukaemias. These can be considered ‘teenage’ cells, which are not yet fully functional. These types of leukaemias develop over months or years.  

4. Who gets leukaemia?

South Africa’s cancer registry is outdated so it is difficult to obtain accurate local statistics. However, international studies2 show the incidence of leukaemia is about 15,8 per 100 000 men and 9,6 per 100 000 women. Between 2003 and 2007, the average age of people being diagnosed with leukaemia was 66 years2. Around 11% were diagnosed under the age of 20 years2. The disease affects white people more than other racial groups and tends to affect men more than women2.

5. Risk Factors for leukaemia

The causes of leukaemia are not completely understood. It does not seem to be hereditary, although genetic abnormalities can cause some types of leukaemias. Researchers have found certain risk factors that increase a person’s risk of getting leukaemia. For example, exposure to large amounts of radiation and certain chemicals such as benzene over a long period of time can increase the risk of developing leukaemia. There is also a possible link between smoking and the disease. 

6. What are the signs and symptoms of leukaemia?

Symptoms to watch out for include fatigue, weight loss, fever, swollen glands, persistent, unexplained bone and joint pain or abdominal fullness1. Spontaneous bleeding is also another sign.

However, it’s important to note that many other benign conditions may also present with similar symptoms. See your doctor if you are in any way concerned or if any of these symptoms persist.  

7. How do doctors test for leukaemia?

The first step in diagnosing leukaemia is a blood test which is conducted to determine blood cell counts. However, the definitive test for diagnosing blood cancers is a bone marrow aspirate or biopsy. Bone marrow aspiration involves the removal of cells from the bone marrow using a needle and syringe. A bone marrow biopsy requires taking a small core of marrow with a biopsy needle. The procedure is usually done under local anaesthesia. 

8. What are “normal” white blood cell counts?

The normal range for white blood cells ranges between 4 000 and 10 000 per micro litre of blood. Infections can also increase the white blood cell count to above the normal range, but this usually normalises when the person gets better. In some cancers though, such as Chronic Myelogenous Leukaemia (CML), patients may have up to fifty times the normal count. 

9. Is leukaemia always characterised by a high white blood cell count?

Not always. In some cases, the leukaemia (or its treatment) can damage the bone marrow so that white blood cell counts actually decrease.   

10. How is leukaemia treated?

Most treatments and therapies aim to destroy and remove all cancer cells. Because most blood cancers represent disorders of rapidly dividing cells, treatments that kill these types of cells, such as chemotherapy and radiation, have been used to successfully treat leukaemia. Bone marrow and stem cell transplants have also proved successful; curing some patients of the disease.

New drug therapies are directed at more fundamental, cellular characteristics that may be unique to specific leukaemic cells. 

11. What is remission?

When the number of cancerous cells in the body is so low that they can no longer be detected in the blood or bone marrow via standard tests, the patient is considered to be in remission. This does not necessarily mean that the patient is cured, as an invisibly small population of cancer cells may remain dormant and lead to a relapse.

12. What are stem cells?

All blood cells in the bone marrow come from an original parent cell, called the stem cell. Stem cells are important because they can be programmed to become any type of cell. In adults, stem cells act as a repair system for the body, replenishing specialised cells but also maintaining the normal turnover of regenerative organs such as the blood, skin or intestinal tissues. 

Stem cells are important in leukaemia because they give rise to all the normal blood cells. Therefore, if there is misprogramming, usually through genetic damage or defects occurring in the DNA of the stem cell, it may give rise to leukaemia if the cell cannot repair these abnormalities.

13. Why is a stem cell transplant needed in some cases of leukaemia?

Chemotherapy may not always kill off all cancerous cells and the patient may be advised to undergo a stem cell transplant. By replacing a person’s malfunctioning stem cells with healthy ones, the body can be reprogrammed into producing healthy blood cells again. The patient’s ‘new’ immune system also kills off the cancerous cells. Only about half of leukaemia patients require a stem cell transplant.

14. What does a donor ‘match’ mean?

In the same way as red cell blood groups exist, so white cells can be categorised into groups known as ‘tissue-types’. During a stem cell transplant, the patient needs to find a donor with a matching tissue type. A match is needed because if not adequately matched, the recipient’s immune system may destroy the donor’s stem cells, or the donor stem cells may recognise the recipient as foreign and start to destroy the recipient’s organs, a condition called Graft-versus-host-disease.

15. How difficult is it to find a donor?

In the past, the chances of finding a bone marrow donor with a matching tissue type were slim. These days, stem cell banks have been established across the world, with over 10 million donors registered worldwide. The process of registration is simple: potential donors submit a blood test and their information is then captured on bone marrow registries. 

Many possible tissue types exist, so finding the correct match depends on how many donors are registered on bone marrow donor registries across the globe. Because most of the existing donors registered are of Caucasian origin, a Caucasian patient has about a 60-70% chance of finding a donor match. For other racial groups, the chances are about 50%. There is about a 25% chance that the patient’s sibling will provide a match. 

16. How is bone marrow donated?

Stem cells can be obtained from the donor’s blood from a machine called a cell separator. This method circumvents the removal of bone marrow from the donor via a syringe and removes the need for him/her to undergo general anaesthesia. This method of obtaining bone marrow collection is less painful and inconvenient for the donor.

17. Are there any side effects for the donor?

Some donors experience slight flu symptoms and low backache from the injections that stimulate their stem cells to move from the bone marrow to the bloodstream, but these are generally limited and well tolerated.

18. What are the risks of a stem cell transplant?

The younger the patient, the better chance they have of surviving a stem cell transplant. Because of this, stem cell transplants are usually reserved for patients younger than 50 years old, although physically fit older patients may be considered. 

19. Why do patients undergo intensive chemotherapy before a stem cell transplant?

Chemotherapy is needed to kill off as many of the cancerous cells as possible before the transplant. It’s also needed to suppress the recipient’s own malfunctioning immune system so that the donor’s immune system can be introduced. If the patient did not undergo chemotherapy, their existing immune system would ‘clash’ with the new one and is likely to destroy the donated stem cells. 

20. Why do most patients stay in hospital for the duration of their treatment?

Patients require large amounts of anti-cancer drugs and it’s easier to do this in hospital. Following a stem cell transplant, patients are particularly vulnerable to infection and need to be isolated from the general public. 

21. Why are most leukaemia patients isolated during their treatment?

Because chemotherapy destroys all rapidly dividing cells – good and bad – a person who is undergoing treatment is particularly susceptible to infections. Doctors advise patients not to go to public places such as shopping malls and cinemas while they are recovering from their treatment.

22. Why does the hair of patients undergoing chemotherapy fall out?

Chemotherapy targets all rapidly dividing cells and does not differentiate between cancerous cells and other rapidly dividing cells. The cells in a person’s hair follicles divide rapidly so the chemotherapy attacks those cells too, causing one’s hair to fall out. 

23. What’s the difference between remission and a cure?

When the number of cancerous cells cannot be detected in a person’s blood or bone marrow by standard tests, they are said to be in remission. While chemotherapy and targeted drugs can bring the number of cancerous cells down to undetectable levels, they do not provide a cure for leukaemia. This is why many patients are required to take their medications regularly, long-term. Meanwhile, stem cell transplants offer a cure and in many cases, patients can go on to live completely disease-free lives. 

24. How do targeted drug therapies work?

Targeted cancer therapies are drugs or other substances that block the growth and spread of cancer by interfering with specific molecules involved in tumour growth. Many of these therapies focus on proteins that are involved in cell signalling pathways, which form a complex communication system that governs basic cellular functions and activities such as, cell division, cell movement, cell responses to specific external stimuli, and even cell death1

By blocking signals that tell cancer cells to grow and divide uncontrollably, targeted cancer therapies can help to stop cancer progression and may also induce cancer cell death. Other targeted therapies can cause cancer cell death directly, by stimulating the immune system to recognise and destroy cancer cells, and/or by delivering toxic substances to them.

25. What are the survival rates for leukaemia?

Survival is measured by how long after diagnosis people live. Cancer survival is measured in a number of different ways. Much depends on the type and stage of leukaemia and when it is diagnosed. 

For example, without treatment, patients diagnosed with first stage Chronic Myelogenous Leukaemia (CML) generally survive between 5-7 years3. The chronic phase of the disease usually extends for 4-5 years before it progresses to the accelerated phase which lasts about 3-18 months. Once a patient progresses to the blast phase, survival is estimated at between 3-6 months3. The survival rate of people diagnosed with acute leukaemias is about 5 years for 50% of patients.

References:

1)      National Cancer Registry. www.cancer.gov. Fact sheet. 

2)      National Cancer Institute. Surveillance, Epidemiology and End Results. http://seer.cancer.gov/statfacts/html/leuks.html

3)      Faderl, S, Kantarjian H, Talpaz M, et al. New treatment approaches for chronic myelogenous leukemia. Semin Oncol. 2000; 27:578-586.

(Bespoke Comm for Novartis, October 2010) 

 
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