Research:

Leukaemia || Colon || Breast || Oral and oesophageal cancer

Leukaemia Research:

What is leukaemia?

 Leukaemia is the cancer of the blood forming cells in the bone marrow.

There are four main types of Leukaemia:

 1) Acute Lymphoblastic Leukaemia (ALL)

2)Acute Myeloid Leukaemia (AML)

3)Chronic Lymphoblastic Leukaemia (CLL)

4)Chronic Myeloid Leukaemia (CML)

The word leukaemia comes from a Greek word which literally means "white blood". Leukaemia is often referred to as cancer of the blood.

The term refers to a group of closely related malignant conditions affecting immature blood-forming cells in the bone marrow.

In leukaemia normal control mechanisms break down and the bone marrow, starts to produce large numbers of undifferentiated white blood cells.

This disrupts the normal production of blood cells leading to anaemia and a low platelet count.

Often in leukaemia the spleen and liver become enlarged splenomegaly and hepatomegaly respectively, and this may cause abdominal discomfort. Also in some cases, the lymph glands (described below) may become enlarged. The large numbers of white cells being produced in leukaemia are all abnormal which means that patients may have frequent, severe infections because the abnormal white cells are being produced in place of normal, infection-fighting cells.

Leukaemia can be classified as lymphoid or myeloid with regard to the origin of the leukaemic cells, and as either acute or Chronic according to the rate of progression of the disease.

Lymphoid and myeloid refer to the type of white cell affected. If this is a lymphocyte or lymphocyte-like cell, the condition is called lymphocytic or lymphoblastic leukaemia. Myeloid leukaemias affect any of the other types of white blood cells or the red cell or platelet producing cells (called megakaryocytes).

The terms acute and chronic are often misunderstood. They refer only to the speed at which the disease progresses if it is left untreated, not to the severity of the disease. Acute leukaemia comes on quickly and, if not effectively treated, will rapidly progress.

Chronic leukaemia is slow to develop and slow to progress, even when not

treated.

 Acute lymphoblastic leukaemia (ALL) is a form of cancer that affects the  lymphocytes and lymphocyte-producing cells in the bone marrow.

Lymphocytes are white blood cells that produce antibodies and are vital parts of the body's immune system. They can be classified into subgroups according to their function - the two main groups are B-cells and T-cells.

In ALL there is an accumulation of immature lymphocyte-forming cells called blast cells in the bone marrow. Eventually, the production of normal blood cells is affected by this and there is a reduction in the numbers of red cells, white cells and platelets in the blood.

Acute lymphoblastic leukaemia is the only form of leukaemia that occurs more frequently in children (under 15 years of age) than adults. When it occurs in adults, ALL is most common between the ages of 15 to 25 and in those over 75 years. The disease is slightly more common in males than in females at all ages.

There are two terms used to describe the leukaemia cells in ALL and they are used together rather than as alternatives. They describe the different properties of the leukaemia cells.

Immunology

The most important classification system is based on the type of lymphocyte lineage affected, that is the B- or T-cell. This is known as the immunological classification and is important in planning treatment. The immunological classification together with characterization of chromosome abnormalities is extremely useful in predicting the response to treatment.

Approximately 20% of adult cases of ALL are T-cell in origin, 75% are early (precursor) B-cell, and 5% are more mature B-cell derived. The mature B-cell type shows some resemblance to a condition called Burkitt's lymphoma and is therefore sometimes called Burkitt-type ALL. Both T-cell

ALL and Burkitt-type ALL have many features in common with non- Hodgkin's lymphoma and are treated with similar drug combinations.

Morphology

The other classification system is mainly based on the appearance of the leukaemia cells (morphology) under the microscope. This is described as the FAB classification after the group of French, American and British haematologists who designed the system. It classifies ALL as L1, L2 or L3. This system is not very important clinically because it does not help in planning treatment or predicting outcomes. The majority of

adult patients with ALL have the FAB L2 type, which further restricts its clinical significance. L3 is the only clearly distinct type within the FAB system .

AML

Acute myeloid leukaemia (AML) is sometimes referred to as acute non-lymphocytic leukaemia (ANLL), especially in American publications. AML is a form of cancer that affects the cells producing myeloid blood cells in the bone marrow. Myeloid cells are red blood cells, platelets and all white cells except lymphocytes. Non-lymphocytic white cells include:

• neutrophils which mainly combat bacterial infection.

• monocytes which destroy more resistant bacteria, give rise to tissue immune cells, called macrophages and are essential for effective function of antibody producing lymphocytes.

• eosinophils which are important to defend against parasites and are involved in allergic reactions.

• basophils which are also involved in allergic reactions and form part of the non-specific defenses triggered by local tissue damage.

In acute myeloid leukaemia the abnormal cells are white blood cells of the neutrophil-type. Occasionally the red blood cells or platelets are affected. Production of blood cells is obstructed and immature cells known as "blast cells" accumulate in the bone marrow. These cells are unable to mature (differentiate) properly leading to a significant reduction of normal blood cells in the circulation. The accumulation of blast cells in the marrow prevents production of other cell types resulting in anaemia and low platelet counts. Blast cells tend to spill-over into the bloodstream which is when they can be picked up by a blood test leading to a diagnosis in most cases.

The types of acute myeloid leukaemia that predominantly affect red cell or platelet producing cells in the bone marrow are known as erythroleukaemia and acute megakaryocytic leukaemia respectively.

How get AML

 Acute myeloid leukaemia affects all ages, but only about 25% of cases occur in people under the age of 25 years. There is an exponential rise in incidence above the age of 40 years. The average age of onset is about 65 years. The incidence is slightly higher in males than in females. American studies have shown a higher incidence of one subtype called acute promyelocytic leukaemia (APL) in people of Hispanic descent.

The FAB classification system for AML recognises eight subtypes called M0 to M7. It is important to stress that these categories do not reflect severity of the disease, for example M0 is neither better nor worse in outlook than M7.

Specialist laboratory tests called histochemistry and immunophenotyping may be of value in some instances. There may be particular difficulty in differentiating some cases of M0, M1 and M7- type A M L from acute lymphoblastic leukaemia (ALL). It is potentially difficult, but very important, to differentiate AML M0 from ALL because the treatment for these two diseases is very different. Both M0 and M7 are distinguished from other forms chiefly on the basis of immunophenotyping. About 50-60% of patients with AML are classified as M1, M2, M3, M6 or M7; about 40%

have M4 or M5 subtypes. The treatment is essentially the same for all except for M3. The latter is also known as acute promyelocytic leukaemia (APL) and effective treatment of this type requires the use of a drug called all-trans retinoic acid (ATRA) alongside standard chemotherapy.

Detailed examination of chromosomes from leukaemic cells shows distinctive abnormalities in almost all cases. The study of these changes is termed cytogenetics and is of value in classifying AML into relative risk groups. The commonest type of change is called a translocation and involves exchange of genetic material between two chromosomes. The implications of such changes are discussed below in the section on treatment planning.

When AML arises on a background of a previously diagnosed bone marrow condition it is known as secondary AML. The distinction is important because secondary AML is more likely to be associated with resistance to standard chemotherapy and has a poorer overall prognosis. Secondary AML is most often seen in elderly patients. In this group it may account for as many as 25 - 40% of cases. AML can occur as a complication of treatment with anti-cancer drugs. This form is referred to as treatment

related AML (tAML) and, like secondary AML, tends to be relatively resistant to standard therapies.

CLL

Chronic lymphocytic leukaemia (CLL) is a form of leukaemia in which there is an excess number of mature, but poorly functioning lymphocytes in the circulating blood. In CLL the major reason for the build-up of tumour cells is the failure of lymphocytes to die at the end of their normal life span. The rate of production of lymphocytes is not significantly increased and may even be slower than normal.

Lymphocytes are white blood cells that are vital parts of the body's immune system. Lymphocytes can be classified into sub-groups according to their function - the main groups are B-cells and T-cells. This is called immunophenotyping. All cases of CLL affect the B-cells. T- cel l leukaemias are extremely rare.

Many patients with CLL also have auto-immune disease, which occurs when the body produces antibodies against its own tissues. The range of conditions includes auto-immune haemolytic anaemia seen in 10% of patients, auto-immune platelet destruction and a combination of both (Evans' syndrome).

About 15% of patients will undergo transformation of CLL to a more rapidly progressing condition - most often chronic lymphocytic leukaemia/prolymphocytic leukaemia (CLL/PLL), in which there are increased numbers of prolymphocytes, or Richter's syndrome (rapidly progressing large cell lymphoma in a patient with CLL). Prolymphocytic leukaemia and Richter's syndrome tend to respond poorly to treatment and have a poorer prognosis than CLL1. At present there is no test available to predict which patients are likely to undergo transformation of their disease, but there is a considerable number of clinical features and laboratory tests which help to predict overall outcome.

How

Chronic lymphocytic leukaemia is overwhelmingly a disease of later life. Only about 10-15% of patients are younger than 50 years of age at the time of diagnosis. While men are more likely to be affected, this seems less marked with increasing age.

The incidence in black and white populations is approximately equal but the disease is rare in Asians. The scarcity in Asians is seen regardless of where they are resident and of their lifestyle which suggests that this may reflect underlying differences in susceptibility.

Ongoing Research:

1) Molecular detection of the fusion gene transcript  in leukaemia

a) In CML bcr/abl fusion gene transcript and its variants in Sudanese patients

b) In ALL (1;19) , (12;21) , (9;22) and (4;11) in Sudanese children

2) Detection of the minimal residual disease using the fusion gene transcripts

This research is funded by the International Atomic Energy Agency

Date of commencement 2003. 

Researchers:            Miss. Sarah Mohammed Ali

                                   Mr. Emadaldin Ibrahim Osman

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Colon

Colon cancer is one of the most common types of cancer; this type of cancer is more accurately referred to as colorectal cancer. In the developed world, three percent to five percent of the population will eventually be diagnosed with colon cancer.

Hereditary nonpolyposis colorectal carcinoma (HNPCC) is an autosomal dominant syndrome, characterized by predisposition to develop a number of cancers including colorectal cancer endometrial, urinary, extracolonic gastrointestinal, brain, and ovarian cancers.

 Other characteristics of syndrome including an early age of onset and development of multiple synchronous and meta-synchronous cancers in some patients.

HNPCC has been shown to be caused by defects in DNA repair genes. In order to determine the responsible genes in Sudanese patients microarray technique has been used for 112 genes involved in DNA repair including:

Direct reversal of damage.Mismatch repair (MMR), base excision repair (BER), nucleotide excision repair (NER), RAD6-dependent pathway and other genome stability genes. Differentially expressed genes will then be investigated by other techniques to identify possible alterations, which will be used further in screening first and second relatives in families. 

Ongoing Research:

1. Molecular characterization of genetic alteration related to colon carcinogenesis (Ghada Hassan).

2. Mutation Analysis of MSH2 and MLH (Ommniyah Elfatih)

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Breast

Breast cancer in Sudan was found to account for 34.5% of all cancers in females and 2.6% in males (Hidayatalla, 1989). The higher frequency of the disease among younger groups, regional and ethnic variation in the distribution of disease underlined the important role of genetics and environmental factors.

Research Areas

1/ Genetic susceptibility:

 Preliminary research included mutation detection of BRCA2 & p53 in a panel of Sudanese breast cancer patients. Results indicated minor role of the two genes among Sudanese, possibility of other susceptibility genes and needs to validate results. We are now studying susceptibility to Breast Cancer: by identifying novel genes and genetic mechanisms involved in the pathogenesis of breast cancer in Sudanese population and then identifying potential mutations in these genes causing the disease among Sudanese.

2/ Epigenetic:

We are investigating the possible role of DNA Methylation as an alternative way of DNA modification during cancer pathogenesis among Sudanese breast cancer patients (CpG methylation of BRCA2). We reported DNA global Methylation in breast cancer pathogenesis.

3/ Immunohistochemistry:

To validate the results obtained by mutation detection we are now conducting protein level investigations to assess defaulted DNA products (proteins) in p53 and BRCA2

4/ Splice junctions:

 To generate correct mature mRNAs the exons must be Identified and joined together in the pre-mRNA splicing process we are looking for mutations affecting the 

 Classical splice signals of BRCA2 gene.

Ongoing Research:

1. Identifying novel genes and genetic mechanisms involved in the pathogenesis of breast cancer in Sudanese population (Mai  Masri)

2. Molecular and Immunohistochemistry screening of P53 tumor suppressor gene among Sudanese breast cancer (Tamader Elzubier)

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Oral and oesophagea cancer

Smokeless tobacco continues to be a significant public health problem despite progress in limiting advertising, requiring product warning labels and implementing preventive education. Oral mucosal lesions, including dysplasia or malignancy are a potential consequence of smokeless tobacco use (Virginia et al., 1994).

Toombak is the native name for tobacco species Nicotina rustica. A coarse powder of dried tobacco leaves is mixed with a concentrated solution of natron (Sodium carbonate) in water until the product is moist and hardened. This product is kept in firmly sealed tin containers for about 2 hours, and then it is ready for use (Idris et al, 1994). It is a smokeless tobacco product that has been in use in Sudan for centuries and is wide spread in the North, East and Central Sudan.

The tobacco specific nitrosamines (TSNAs) are considered to be major contributors in the induction of cancers of the areodigestive tract in tobacco chewers, snuff dippers and smokers (Klien et al., 1992, Lazarus et al 1996).

A likely candidate for toombak induced genetic alteration is the p53 tumor suppressor gene (Lazarus et al., 1996). Mutations of p53 gene have been observed in 37% of human head and neck tumors, 45% of human esophageal tumors, and 56% of human lung carcinomas (Greenblatt et al., 1994).

A statistically significant increased incidence in mutations of the P53 genes was found in OSCC from toombak dippers as compared with those from non-dippers in Sudan ( Ibrahim et al 1999 ).

Ongoing Research:

Mutational analysis of the conserved portion of the p53 tumor suppressor gene among Sudanese oral and esophageal cancer patients (Nahid Gornas)

Patients in this study were Sudanese with oral and oesophageal cell carcinoma living in different areas of Sudan. Patients were selected regardless to age or sex or duration of infection.

In trying to establish the frequency of P53 mutation among oral and esophageal patients in Sudan, the heteroduplex analysis was used as a screening tool, hunting for mutations in p53 exon 5-9 as many studies reported that the majority of mutations in p53 occur in the highly conserved regions in exon 5-8 (Hollstein, 1991).

Using this technique eleven samples out of twenty were detected mutated (55%). Those samples were further subjected to SSCP (Single strand conformation polymorphism) method for conformation. Six were confirmed using the latter method (30%).

Due to financial limitations only four samples out of the six which were detected by both methods (HD/SSCP) were sent for commercial sequencing, three of them were confirmed to be mutated (75%).

We recommend, a large epidemiological study running in parallel with a genetic study to compare ethnic group differences with environmental habits like smoking, dipping tobacco and alcohol drinking.

References:

-Greenblatt M.S., Bennet W.P., Hollstien M. (1994). Mutations in the p53 tumor suppressor gene, clues to cancer etiology and molecular pathogenesis. Cancer Research: 54: 4855-4878.

-Hollstein M., Sidrnsky D., Vgelstein B. (1991). P53 mutations in human cancers. J. Science:253:49-53.

-Ibrahiem S.O., Endre N. Vasstrand., Anne C. Jannessen., Ali M. Idris., Bengt M., Rune N., and John R. Lillenang. (1999). Mutations of the p53 gene in oral SCCs from Sudanese dippers of rich Toombak and non snuff dippers from Sudan and Scandinavia. Int. Dentist J: 41: 365-375.

-Idris A.M., Prokopezyk B., and Hoffman. (1994). Toombak: A major risk factor for cancer of the oral cavity in Sudan. J. Preventive Medicine: 832-839.

-Klien-Szanto A.J.P., Lizasa T., Momiki S. (1992). A tobacco specific N- nitrosamine or cigarettes condensate causes neoplastic transformation of xenotransplanted human bronchial epithelial cells. J. National academic science , USA: 89:6693-6697.

-Lazarus P., Stem J., Zwiebel N., Fair A., Ritchie J.P.JR., and Schantz S. (1996).

Relationship between p52 mutation incidence in oral cavity SCC and patient tobacco use. Carcinogenesis: 17: 733-739.

-Virginia S., Daughety M.S., Steven M., Levy D.D.S., M.P.H., Kristi J., Ferguson P.H.D., Paul R. (1994). Surveying smokeless tobacco use, oral lesions and cessation among high school boys. Jada, volume 125.

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