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by Avinash Deo

Superior Vana Caval Syndrome


Superior Vena Caval Syndrome (SVCS) results from a space occupying lesion (SOL) in the superior mediastinum. The presence of a SOL results in compression of structures passing through the mediastinum. The most prominent clinical manifestations result from compression of superior vena cava and for this reason it is also referred as superior vena caval syndrome. Superior mediastinal syndrome,  a term that captures the pathogenesis of the syndrome, is also used. SVCS was first described by William Hunter in 1757 in a patient with syphilitic aortic aneurysm. Today the most common cause is a malignancy.

Anatomy of the Superior Mediastinum

Superior mediastinum is bound

  1. Inferiority by an imaginary plane running from the sternal  angle to the fourth thoracic vertebra,
  2. Superiority by the thoracic inlet
  3. Anterior by manubrium of the sternum
  4. Posteriorly by the bodies of first four thoracic vertibrae.
  5. Laterally by the pleura.

It is space through which tubular structures pass from the neck to the thoracic organs. These include the following

  1. Arch of the aorta and its branches including Brachiocephalic artery, Left Common carotid artery, Left Subclavian artery – to the left upper limb.
  2. Superior Vena Cava and its tributaries Brachiocephalic veins, Left superior intercostal vein, Supreme intercostal vein, Azygos vein
  3. Lymph nodes draining the lung are found in the fatty tissues.
  4. Oesophagus

Pathogenesis of SVCS

Superior mediastinum has rigid walls, making the structures passing through it prone to compression by mass lesions. The commonest cause of compression is a malignancy arising from or involving structures of superior mediastinum. Lung cancer and lymphoma being the two commonest causes of SVCS. Some conditions like Mediastinal fibrosis may constrict rather than compress the mediastinum. Indwelling vascular lines has increased the risk of thrombosis of superior vena cava common. One needs to consider the possibility of thrombosis in patients who have indwelling venous access devices.  The table lists the causes of superior vena caval syndrome.

Malignant Non-Malignant
  1. Lung cancer
  2. Lymphoma
  3. Others: metastatic cancers, primary leiomyosarcomas of the mediastinal vessels, plasmocytomas
  1. Mediastinal fibrosis
  2. Vascular diseases, such as aortic aneurysm, vasculitis, and arteriovenous fistulas
  3. Infections, such as histoplasmosis, tuberculosis, syphilis, and actinomycosis
  4. Benign mediastinal tumors such as teratoma, cystic hygroma, thymoma, and dermoid cyst
  5. Cardiac causes, such as pericarditis and atrial myxoma
  6. Thrombosis related to the presence of central vein catheters

Manifestations

The common manifestations of superior vena cava syndrome include

  1. Dyspepsia
  2. Swelling of the face and upper extremities
  3. Cough, chest pain
  4. Dysphagia

Examination shows distended neck veins and chest wall oedema, plethora of face, and oedema of the arms.

Diagnosis

Radiology: Radiograph of chest usually shows a mediastinal mass. If not this is apparent of on a CT scan. The CT scan is also needed to define extent of disease and invasion of the great vessels, bronchus, and the spinal cord.

Biopsy and Cytology: The investigations to establish diagnosis include sputum cytology, examination of pleural fluid (if present) and histology. The tissue for histological examination may be obtained by bronchoscopy, thoracoscopy, mediastinoscopy guided lymph node biopsy, CT guided core needle biopsy of the mass. A bone marrow examination may be of value if the haemogram is abnormal. A careful examination of the supraclavicular region shows nodes in about 2/3rd of the patients with SVCS which can be biopsied.

Treatment

The aim of treatment of SVCS is to relive symptoms at the same time not compromise diagnosis or the possibility of cure. All patients should be given head elevation and oxygen. Diuretics can reduce oedema but this comes at the cost of dehydration. Tissue must be obtained for diagnosis. Unless there has been a substantial delay in diagnosis, initiation of treatment is not an emergency and tissue can be obtained. Vascular stents can be inserted in patients who are very symptomatic to relieve symptoms till diagnosis is made. 

The treatment of SVCS is disease specific. Chemotherapy with or without radiation is indicated in patients with lung cancer (small cell as well as non-small cell). The response rate in small-cell lung cancer exceeds 90% with 70% of the patients remaining disease free. Addition of radiation to chemotherapy reduces the risk of recurrence. About 60% of the patients with non-amall cell lung cancer respond to therapy. The disease recurs in about 20% of these. Patients with NSCLS presenting with SVCS have a poorer survival than those who do not. Lymphoma is treated with chemotherapy. 

Catheter-induced SVCS may be treated with thrombolytic agents early (< 5 days) in the course of the disease. Catheters of patients with prolonged symptoms should be removed and this should be done under cover of heparin.

Patients who have cancers that do not respond to chemotherapy or radiation can be palliated by placement of vascular and tracheal stents where possible.

by Avinash Deo

The M-Band


Monoclonal Gammopathy-02

Figure 1. Each plasma cell produces a different type of antibody. Normal γ globin band is depicted in the left column. The plasma cell numbers are normal and each produces an antibody with a different amino acid structure and electrophoretic mobility. Patients with monoclonal gammopathy have expansion (increase number) of a plasma cell clone (red in the diagram) resulting in the production of a disproportionate large amount of immunoglobulin from one type of plasma cell. This results in the M Band (see below). Patients with polyclonal gammopathy have an expansion (increased number) of plasma cells. This is usually occurs in response to infection/inflammation that result in production of a diversity of antibodies. The diversity is reflected in increase in the γ but as no one clone dominates the sharp M band is not seen.

What is an M-Band?

Immunoglobulins are antigen binding molecules secreted by plasma cells. Immunoglobulins bind antigens and play a role acquired immunity. Plasma cells develop from antigen exposed B-lymphocytes. The process of maturation of lymphocytes involves inducing mutations in region of the immunoglobulin gene that encodes for antigen binding regions, the hypervariable regions. This makes the DNA and consequently the amino acid sequence of the immunoglobulin secereted by a plasma cell unique. This is true even when two plasma cells make antibody against the same antigen or antigenic epitope (see figure 1).

Monoclonal Gammopathy-01

Figure 2. The serum protein separate into many bands on electrophoresis. The albumin is a dark band closest to the anode. This is followed by the α1, α2, β and γ bands. The immunoglobulin are mainly found in the γ globulin band but some may be found in the β globin band. The electrophoretic mobility of a molecule depends on the charge it carries which in turn depends on the amino acid sequence. Amino acid sequence determines the antigen specificity and differs between antibodies resulting in a slight variation in electrophoretic mobility of immunoglobulins and resulting in the γ region being a broad band.


The amino acid sequence determines the charge on the immunoglobulin. The electrophoretic mobility is determined by the charge. Majority of the immunoglobulins move to the γ-globulin fraction of serum proteins, some move with β-globulin. The γ-globulin band is a wide electrophoretic band reflecting the diversity in electrophoretic mobility of immunoglobulins arising from the diversity in amino acid sequences (figure 2).

Monoclonal Gammopathy-03

Figure 3. Patinets of monoclonal gammopathies have an expansion of one clone of plasma cells. This reflects in production of a disproportionally large amount of immunoglobulin with identical electrophoretic mobility resulting in a dense band with in γ globin region


Patients of monoclonal gammopathies have clonal expansion of plasma cells. The cells of a clone have identical DNA and produce identical immunoglobulin molecules. When the clone grows to level that it forms a significant proportion of the plasma cell pool the immunoglobulin it produces forms a significant proportion of the total serum immunoglobulins. The identical electrophoretic mobility of molecules produced by the clone results in a disproportionately large number of immunoglobulin concentrating to a point on electrophoresis forming a band.  This is known as the M band.  Lymphoma cells, notably those of lymphoplasmacytic lymphoma, can secrete immunoglobulin and are associated with an M band for similar reasons.

Diseases associated with an M-Band

The M-Band is a serum marker for plasma cell dycrasias and Waldenström macroglobulinemia. IgM and non-IgM (mainly IgG and IgA) monoclonal bands have differing clinical implications. The former is more commonly associated with lymphoproliferative disease and the latter with plasma cell dycrasias. The presence of an M band only indicates a clonal expansion of immunoglobulin producing cells. It does not indicate malignancy. The diagnosis of malignancy is made by features that suggest end organ damage. The absence of end organ damage indicates a premalignant disease including monoclonal gammopathy of uncertain significance (MGUS), soldering multiple myeloma or smoldering Waldenström macroglobulinemia.  The evidence of end-organ damage includes

  1. non-IgM Monoclonal Gammoathies: CRAB (elevated calcium, renal involvement, anaemia and osteolytic (bone) lesions) creatinine,
  2. IgM Monoclonal Gammapathies: Anemia, constitutional symptoms, hyperviscosity, lymphadenopathy, or hepatosplenomegaly that can be attributed to the underlying lymphoproliferative disorder if diagnosis is Waldenström macroglobulinemia or CRAB (elevated calcium, renal involvement, anaemia and osteolytic (bone) lesions) creatinine if the diagnosis of IgM myeloma

False positive M-Band

The presence of M band indicates presence of a clonal expansion of plasma cells. When end organ damage co-exists with M band a diagnosis of a malignancy (multiple myeloma or Waldenström macroglobulinemia) is made. In the absence of end organ damage the diagnosis of a premalignant disease is made. Proliferation a of plasma cells are seen in infections/inflammation. These are polyclonal and result in s polyclonal gammopath. They do not result in the presence of an M-band.

 

 

by Avinash Deo

Anaemia with Hyperbilirubinaemia


A 49-year-old female presented with dyspnoea on exertion of 1 month duration. Examination reviled pallor and icterus. There was no lymphadenopathy, clubbing, koilonychia, platonychia, petechiae or purpura. There was no oedema of feet. The pulse was 90/min and the blood pressure 130/70 mm of Hg. Examination of the respiratory, cardiac and nervous systems did not show any abnormality. There was no organomegaly.

The haemoglobin was 4.9 g/dL with an erythrocyte count 1.37 x 1012/L, haematocrit of 16%, MCV of 116.78 fL, MCH of 35.77 pg and MCHC 30.63 of g/L.  The leucocytes count was 2800 with 35% neutrophils and 65% lymphocytes. The platelet count was 90 x 109/L. The peripheral smear showed macrocytosis and anisocytosis. Hypersegmented neutrophils were seen. The reticulocyte count was 3%.

The bilirubin was 2.1 mg/dL with a direct bilirubin of 1.8mg/dL and an indirect bilirubin of 0.3mg/dL. The Lactate dehydrogenase was 1417IU (normal 105 – 333 IU/L).

Anaemia and unconjugated hyperbilirubinaemia are characteristic of haemolysis. Does this patient have haemolytic anaemia?

Haemolysis shortens erythrocyte lifespan and results in increases haemoglobin breakdown. Haemoglobin is made of heme and globin. Heme consists of porphyrin ring at the centre of which is iron in the ferrous state. Iron released from catabolism of heme is reused. The porphyrin ring is catabolised to bilirubin. The bilirubin is transported to the liver for conjugation and excretion (see haemoglobin catabolism). Patients of haemolytic anaemia have unconjugated hyperbilirubinaemia because the increased bilirubin production overwhelms the hepatic bilirubin conjugation capacity.

One of the characteristics of megaloblastic anaemia is ineffective erythropoiesis. Ineffective erythropoiesis is defined as a sub-optimal (fewer) production of mature erythrocytes from a proliferating pool of immature erythroblasts. Each immature erythroblast produces less than the optimal number of erythrocytes because of premature death of erythroid precursors including haemoglobinized precursors. The haemoglobin released from haemoglobinized erythroid precursors is catabolised in the same manner as haemoglobin released from lysed erythrocytes (see haemoglobin catabolism). Megaloblastic anaemias are associated with unconjugated hyperbilirubinaemia because of death of haemoglobinized erythroid precursors.

The treatment of haemolytic anaemia and megaloblastic anaemia are different? How does one differentiate megaloblastic anaemia from that because of haemolytic anaemia? Does this patients have a haemolytic anaemia or megaloblastic anaemia?

Haemolytic anaemia is characterised by shortened erythrocyte survival. Erythrocytes survival is estimated by the use of radionucleotides something that is not possible at most centres. In clinical practice, a shortened erythrocyte survival is inferred from a high reticulocyte count. Reticulocytes are erythrocytes that have been produced in the preceding 24 hours. The erythrocytes survival is about 120 days and about 1% of erythrocytes are produced every day. Consistent with this the normal reticulocyte count is 0.5-1.5%.In patients of haemolytic anaemia, ddestruction of erythrocytes is matched by an increased production by the bone marrow. This manifests as reticulocytosis (see reticulocyte count). Megaloblastic anaemia occurs because of decreased production of erythrocytes and this manifests as reticulocytopenia. The difference between haemolytic anaemia and megaloblastic anaemia is the reticulocytosis in the former reticulocytopenia in the latter. This patient had a high reticulcoyte count but after correction both the reticulocyte production index [0.43] and corrected reticulocyte count [1.07%] were low excluding haemolysis. This patient was evaluated for megaloblastic anaemia.

The haemogram has clues to differentiate between haemolytic anaemia and megaloblastic anaemia. These include

  1. A very high MCV: The MCV is very high. Patients with haemolytic anaemia have a mild elevation in MCV. An MCV value >110fL is almost exclusively found in megaloblastic anaemias because of folate and/or B12 deficiency.
  2. Pancytopenia: B12 and folate deficiency impair DNA synthesis impairing erythrpoieis, myelopoiesis and megakaryopoiesis. Nutritional megaloblastic anaemias because of vitamin B12 and/or folate deficiency may show pancytopenia.
  3. Hypersegmented neutrophils (>5% neutrophils with >5lobes) is a feature of megaloblastic anaemia

Other features of megaloblastic anaemia include rise serum transferrin receptor, increased serum iron, serum ferritin and methemalbumin levels. Like haemolytic anaemia the serum haptoglobin is low and the LDH high. LDH levels in megaloblastic anaemia can ve very high.

This patients had a low serum B12 and was treated with parental B12 (1mg alternate day for 5 doses) and was evaluated for cause of vitamin B12 deficiency. As Schilling’s test was not available a diagnosis of pernicious anaemia was made by documenting gastric atrophy and anti-parietal cell antibodies.

by Avinash Deo

Calreticulin and Myeloproliferative Disease


Myeloproliferative disorders (polycythaemia vera [PV], essential thrombocytosis [ET], progressive myelofibrosis [PMF]) are a group of diseases that are characterised by increased proliferation of blood cells, splenomegaly, myelofibrosis, thrombosis and risk of malignant transformation.  The year 2005 was a landmark year for myeloproliferative diseases. Four groups of scientists identified the presence of JAK2V617F mutations in PV. This mutation is present in about 98% patients with PV. Mutations of exon 12 of the JAK2 gene can be found in 1-2% of the PV. These patients do not show the JAK2V617F mutation. The discovery of these mutations gave a genetic definition PV making diagnosis objective.

PV is diagnosed by the presence primary erythrocytosis in the precession of a JAK2 mutation referred to above. Chronic myeloid leukaemia is diagnosed by demonstrating the BCR-ABL1 translocation. JAK2V617F is also present in 50-60% of ET and PMF. Mutation of the gene MPL is found in 1-2%  patients of ET and 5-10% of the patients with PMF. The presence of these mutation helps make diagnosis. However, The diagnosis of PMF and ET in a large proportion of patients requires exclusion of a reactive disorder and other myeloproliferative diseases because these patients (38-49% of ET and 30-45% of PMF) have no genetic marker.

Two publications have shown that a large proportion of the patients with ET and PMF who do not have JAK have mutation calreticulin (CALR) (N Engl J Med. 2013;369(25):2391-2405,  N Engl J Med. 2013;369(25):2379-2390). In addition to ET and PMF CALR mutations are found in the MDS/MPN overlap disorder and refractory anemia with ring sideroblasts with thrombocytosis (RARS-T). They are rare or absent in other myeloid or lymphoid neoplasms or solid tumors.

Calreticulin (CALR) is a major calcium binding protein. The gene for calreticulin is located on 19p13.2. About a quarter of ET and MF have mutation in the CALR gene. All CALR mutations are localised to exon 9 and generate a 1bp frameshift. As a result of this most or almost all the C terminal negative amino acids and calcium binding sites are lost.  There is a complete loss of the KDEL endoplasmic reticulum binding sequence. These mutations have been identified in the haemopoietic stem cell and progenitor compartments. CALR mutations and JAK2 mutations are mutually exclusive.

CALR mutated myeloproliferative disease have a distinct clinical profile. These patients have a lower haemoglobin, lower leukocyte count, higher platelet count and a lower risk of thrombosis. Patients of PMF carrying a CALR mutation have a longer survival than those carrying JAK2 or MPL mutations. Patients with ET carrying the CALR mutations have a longer survival than those carrying the JALK2 mutation. There is no difference between the survival of ET patients carrying CALR mutations and MPL mutations.

Mutated CALR appears to stimulate STAT pathway. It appears to physically bind with the thrombopoietin receptor to stimulate STAT. The erythropoietin receptor is not needed for this action (Blood. 2015;10.1182/blood-2015-11-681932, Blood. 2015;126:LBA-4).

 

 

 

by Avinash Deo

Chronic Myeloid Leukaemia



Chronic myeloid leukaemia (CML) is a myeloproliferative disorder characterised by anaemia, leucocytosis and splenomegaly. The natural history of CML is characterised by three phases chronic phase, accelerated phase (AP) and blast phase (BP). CML is characterised by the presence of fusion gene BCR-ABL1 that results from the t(9;22) translocation. This gene encodes for a constitutionally active tyrosine kinase that has been shown to drive the CML stem cells. The diagnosis of CML can not be made in the absence of this gene.  Onset of AP signals a change in the biological behaviour of disease. The disease follows a more agressive course that culminates in blast phase. The blast phase mresembles an acute leukaemia and is a terminal event in the natural history of CML. Inhibitors of BCR-ABL1 prevent the emergence of accelerated and blast phase and have dramatically improved the outcome of CML.

Etiology and Epidemiology

CML constitutes about 15% of all leukaemias. The incidence increase with age and the disease is slightly more common in males. The incidence of the disease does not show geographic variation. The only know etiological factor for CML is exposure to radiation.

Pathogenesis

CML is characterised by the presence of Philedelphia chromosome [t(9;22)(q34;q11)] which results from a reciprocal translocation between the long arms of chromosomes 9 and 22 (figure 1). The ABL1 proto-oncogene is located on chromosome 9 at q34. Chromosome 22 has the BCR gene at 22q11. The ABL1 gene translocates downstream to the BCR gene as a result of the t(9;22)(q34;q11) translocation. This results in the formation of the BCR-ABL1 fusion gene (see The BCR-ABL1 Gene).

Molecular Biology of CML

 

The expression of the ABL1 tyrosine kinase is tightly regulated. The t(9;22)(q34;q11) results in the N terminal segment of the ABL1 gene being replaced by that of the  BCR gene. This results in the ABL1 tyrosine kinase being constitutively expressed. The size of the N terminal amino acids contributed by BCR determine the length and the clinical properties of the fusion gene.

A model of pathogenesis of CML has to account for three features of the disease

  1. Uncontrolled proliferation of leucocytes accompanied sometimes with the proliferation of platelets
  2. Progression from a relatively stable phase of proliferation, the chronic phase, to a agressive  phase charecterized by increasing leucocytes counts, anaemia and falling platelet counts ultimately culminating in a acute leukaemia like picture, the blast phase. Unlike the chronic phase that shows myeloid and sometimes platelet proliferation, the blast phase may show a myeloid, lymphoid or rarely megakaryocytic lineage.
  3. Failure of tyrosine kinase inhibitors to errdicate the malignant clone despite pronounced and prolonged supression of the BCR-ABL1 positive clone.

The precise mechanism how BCR-ABL1 leads to chronic myeloid leukaemia is not known. Activation of phosphatidylinositol kinase (PI3K), RAS/Mitogen activated protein kinase (RAS/MAPK) and JAK/STAT pathway has been demonstrated in BCR-ABL1 positive cells. These pathways have been implicated in malignant transformation of cells and are believed to be responsible for the malignant phenotype of CML. Progression of CML from chronic phase to accelerated phase and eventually blast phase marks change in the disease that makes it progressively less responsive to drugs inhibiting BCR-ABL1 kinase. Cells with BCR-ABL1 fusion gene have an increase in the reactive oxygen species predisposing them to DNA damage. Progression from chronic phase to acclerated phase and eventually blast phase is associated with the cell accquiring additional mutations. This is known as clonal evolution. Reactive oxygen species induced DNA damage is believed to result in clonal evolution which results in progression to accelerated phase and blast phase resulting in treatment failure.

CML Pathogenesis-600px

Imatinib, an inhibiter of ABL1 tyrosine kinase has been in use for over a decade. Treatment of CML patients with Imatinib results in normalisation of blood counts, regression of splenomegaly and a decrease in the number of cells showing BCR-ABL1 fusion gene. The BCR-ABL1 kinase expressing cells are suppresses to undetectable levels in about 40% of the patients creating an impression that disease has been eradicated. If treatment is discontinued in such patients cells expressing BCR-ABL1 fusion reappear in 50-60% of such patients. These observations have been interpreted as suggesting that the CML stem cells have mechanisms that survive inhibition by Imatinib and other inhibitors of ABL1 tyrosine kinase. Studies to identify and target these pathways to erradicate CML stem cells with an goal to curing CML are undertaken. Some of the pathways that have shown a promise are Alox5pathway, the sonic hedgehog pathway (SHH), the Wnt/β-catenin pathway, the JAK/STAT pathway, the TGF-Beta/FOXO/BCL-6 pathway (Stem Cells International Volume 2013 (2013),  Article ID 724360, 12 pages)

Clinical Manifestations

Presentations

The manifestation of CML included

  1. Anaemia
  2. Fatigue, weight loss, fever, night sweats because of a hyper metabolic state induces by high leucocyte counts
  3. Bone pain
  4. Abdominal pain, early satiety and fullness because of splenomegaly. The pain is usually a tugging pain but sharp pain may indicate a splenic infarct. Splenic rupture though described is a rare event.
  5. Leucostasis because of very high white blood cell counts may present with neurological deficits, respiratory insufficiency or priapism.
  6. Incidental discovery for a haemogram performed for another reason is becoming a common presentation in populations that have a good healthcare system.

Splenomegaly is commonly seen. Historically CML is associated with massive splenomegaly (splenomegaly below the umbilicus). Today this may be seen only in communities with suboptimal health care and diagnosis is delayed. Hepatomegaly may be seen in some patients.

CML-Phases

Stages of Disease

CML has three stages, chronic Phase, accelerated phase and blast phase. Before the introduction of definitive therapy (Initially interferon, currently inhibitors of BCR-ABL1 kinase) every patient progressed from chronic phase to accelerated phase and finally to blast phase. The blast phase was terminal. The WHO definitions of the phases are listed in table 1. Acclerated phase definition is defined differently by different authors. Definitions may differ in the details but recognise the following

  1. Increasing WBC counts with appearance of new anomalies. These may be basophilia, eosinophilia or increase in the immature forms particularly blasts and promyelocytes. Progression of patients on BCR-ABL1 kinase inhibitors is accompanied by appearance mutations in BCR-ABL1.
  2. Increasing splenomegaly

The TKIs have dramatically reduced the rate of progression to accelerated phase or blast crisis. 4.6% for Dasatinib (DASSISION trial 5 year follow up), 3.5% for nilotinib (ENESTnd)and 8% imatinob (IRIS trial 8 Year follow up). Patients who do not achieve an early response to TKIs have a higher risk of progression.

Investigation

Haemogram

A complete haemogram should be performed in all patients. Patients of CML have leucocytosis with shift to the left and often have eosinophilia and/or basophilia. Platelet counts are often slightly increased but may be normal high or occasionally low. There is mild to moderate anaemia. The differential count of peripheral blood depends on the phase of disease. Patients with chronic phase have <10% blasts and ≤ 20% basophilis. Patients with accelerated phase have 10-19% blasts or >20% basophilic. Patients with blast crisis have ≥20% blasts.

Bone Marrow

Bone marrow studies are not needed for diagnosis of CML. This can be made by demonstration of BCR-ABL1 on peripheral blood. Bone marrow studies are essential for determining the phase of disease. The bone marrow of a patients of chronic phase of CML shows a high myeloid to erythroid ratio with a normal myeloid maturation. Dysplasia is not a feature of CML and suggests the diagnosis of myeloproliferative disease/mydlodysplasia overlap.  The chronic phase is characterised by <10% blasts. The megakaryocytes are smaller with reduced lobulation and may be increased in number. Bone marrow of patients from accelerated phase show myeloid hyperplasia with myelodysplasia and a blast percentage between 10-19%. Megakaryocytes may be seen in clusters or sheets. Bone marrow from patients with blast phase shows ≥20% blasts.

Risk Scores

Risk scores help in prognosticating the patients and should be performed at diagnosis. The three scores are listed in table 2. Hasford and Sokal scores are prognostic scores for predicting outcomes of CML patients. The  EUTOS score was developed to predict the outcome of patients receiving imatinib at 18 months of therapy and was reported to perform better than Sokal and Hasford scores. It has not been validated by other investigators.

CML Prognostic Scores

Table 2. CML Prognostic (Risk) Scores

 

Treatment

The approval of imatinib in May 2001 by the US FDA saw CML become the first disease to benefit from targeted therapy. The 8 year survival of patients in chronic phase has improved from 6% in 1975 to 42%-65% from 1983-2000 and 87% for patients diagnosed after 2001 (Blood 119:1981-87;2012). Before the introduction of imatinib the treatments used for patients of CML included (in chronological order) splenic radiation, arsenic, busulfan, hydrourea and a combination of interferon and cytarabine. With the exception of interferon and cytarabine none of the other therapies suppress the BCR-ABL1 positive clone.  The IRIS trial established imatinib, an inhibitor of BCR-ABL1 tyrosine kinase as the first line treatment for chronic myeloid leukaemia. DASSISION trial and the ENESTen trials established dasatinib and nilotinib as front line therapy.
 The aims of therapy is prevent progression of disease to accelerated phase and blast phase. This can be achieved by
  1. Inducing a haematological remission
  2. Inducing a molecular remission
  3. Eradicating the CML stem cell

Tyrosine kinase inhibitors (TKIs) are the first line of treatment in all patients of CML. The use of imatinib in pregnancy is associated with increase in malformations. These include malformations of the skeleton, respiratory system, kidney and gastrointestinal the gastrointestinal tract. The risk of exompholous is increased by almost 1000 times. Imatinib and other TKIs are contraindicated in pregnancy. The treatment of pregnant woman is challenging. Interferon may be used after the period of organogenesis. Women who have not completed their family are encouraged to do so early and should be switched to TKI. Women in the childbearing age on TKI should be made to understand that contraception is mandatory.

Tyrosine Kinase Inhibitors (TKI)

Many inhibitors of BCR-ABL1 tyrosine kinase have been developed. Out of these imatinib, dasatinib and nilotinib are approved for use in the first line setting. Dasatinib and nilotinib can be used for patients who relapse on imatinib. Busotinib and ponatinib are approved for use relapsed CML. The TKIs drugs used in CML are listed in the table below.

 Dose Indications Adverse Effects
Imatinib
  1. Chronic Phase CML: 400mg
  2. CML AP/BP: 400mg od the doses may be increased to 600mg-800mg/day. The 800mg dose is administered in two daily doses
  3. Ph+ALL: 600mg od
  4. PDGFRA mutated MDS/MPD: 400mg/day
  5. GIST: 400mg/day
  6. HES/CEL: 400mg od
  1.  CML First line therapy for chronic, accelerated and blast phase
  2. Ph+ve ALL
  3. Gastrointestinal stromal tumour
  4. MDS/MPD with PDGFA gene rearrangements
  5. Hypereosainophilic syndrome/chronic eosinophilic leukaemia
  1. Skin depigmentation
  2. Nausea, vomiting
  3. Periorbital oedema
  4. Fluid retention manifesting as effusions and oedema
  5. Myalgias
  6. Diarrhoea
  7. Insomnia, deprtesson
Dasatinib
  1. Chronic Phase: 100mg od
  2. Accelerated and blast phase: 140mg od
  1. CML first line and second line therapy
  2. Ph+ve ALL resistance or intolerance to prior tyrosine kinase therapy
  1. Myelosupression
  2. Bleeding
  3. Fliud retention manifestion as oedema and pleural effusion
  4. Diarrhoea, nauseas vomiting
  5. Fatigue
  6. Insomnia, depression
  7. Elevated transaminases
  8. Hypocalcaemia, hypophosphataemia
  9. QTc prolongation
Nilotinib
  1. CML Chronic Phase 300mg bd
  2. CML chronic phase resistant/intolerant to other TKIs: 400mg bd
  3. AP/BC: 400mg bd
 CML first line and second line therapy

 
  1. Myelosupression
  2. Fatigue, asthenia, anorexia
  3. Prolonged QTc
  4. Electrolyte anomalies – hypophosphatemia, hypokalemia, hypocalcaemia, hyponatraemia
  5. Elevated transaminases
Bosutinib
  1. CML chronic phase: 500 mg orally once daily with food. Escalation to 600 mg daily in patients who do not respond.
  2. Dose in Hepatic impairment: Reduce 200 mg daily
 CML failure or intolerance to firstling therapy
  1. Diarrhoea
  2. Nausea/vomiting
  3. Abdominal pain
  4. Myelosupression
  5. Skin rash
  6. Elevated Transaminases
  7. Fliud retention manifestion as oedema and pleural effusion
  8. Fatigue
Ponatinib
45mg reduce dose to 30mg in patients taking strong CYP3A inhibitors
  1. CML first line and second line therapy
  2. Ph+ve ALL resistance or intolerance to prior tyrosine kinase therapy
  3. The only TKI active against the T315I BCR-ABL1 mutation
  1. Arterterial thrombosis including myocardial infraction. Toxicity may be seen in up to 10% of the patients
  2. Cardiac toxicity – arrhythmias, pericardial effusions
  3. Elevated transaminases,  liver failure
  4. Pancrititis
  5. Hypertension
  6. Fluid retention,
  7. Gastrointestinal perforation
  8. Tumour lysis syndrome
Omacetaxine (Non TKI, inhibitor of protein synthesis)
 1.25mg/m2 SC bd for 14 consecutive days every 28 days till haematological response. Continue as 1.25mg/m2 sc bd for seven days every 28 days after as maintenance CML chronic or acclerated phase resistant to two more TKI
  1. Myelosupression – thrombocytopenia, neutropenia and anaemia
  2. Impaired glucose tolerance with hyperglycaemia in upto 11%
  3. Diarrhoea, nausea, vomiting abdominal pain
  4. Fatigue asthenia, arthralgia peripheral oedema
  5. Injection site reactions

A newly diagnosed patients should be initiated on treatment with Imatinib (400mg od), dasatinib (100mg od)  or nilotinib (300mg bd). Dasatinib and nilotinib. Busotinib and  ponatinib can be used in patients progressing on these the first line drugs. Ponatinib is indicated in the T315I mutations. Patients carrying this mutation do not respond to any of the other TKI.

Monitoring Therapy

Patients are monitored for response by clinical examination, haemogram and determining the levels of the BCR-ABL1 transcript. The BCR-ABL1 transcript is measured by RT-PCR. The response definitions are given in table below

Response Definitions

Complete Haematological Response
  1. WBC counts < 10 X 109/L
  2. Platelet Count < 450 X 109/L
  3. No immature myeloid cells on the peripheral blood differential count
  4. Basophils less than 5%
  5. no splenomegaly
Cytogenetic Response
  1. Complete (CCyR) 0% Ph+
  2. Partial Cytogenic Response  (PCyR) 1-35%
  3. Major Cyogenic response 36%-65%
  4. Minor Cytogenic Response 66%-95%
  5. No Cytogenic Response >95%
Molecular Response
  1. Early molecular response (EMR) – BCR-ABL1 transcripts ≤10% by QPCR (IS) at 3 and 6 months.
  2. Major molecular response (MMR) – BCR-ABL1 transcripts 0.1% by QPCR (IS) or ≥3-log reduction in BCR-ABL1 mRNA from the standardized baseline, if QPCR (IS) is not available.
  3. Complete molecular response (CMR) – no detectable BCR-ABL mRNA by QPCR (IS) using an assay with
  4. a sensitivity of at least 4.5 logs below the standardized baseline. CMR is variably described, and is best defined by the the assay’s level of sensitivity (eg. MR 4.5).
Relapse Resistance
  1. Any sign of loss of response (defined as hematologic or cytogenetic relapse)
  2. 1-log increase in BCR-ABL transcript levels with loss of MMR (two consecutive samples to be tested)
  3. loss of CCyR

The haematological and cytogenetic milestones in the treatment of CML have been described by the NCCN and ELN.  Secondary resistance to TKIs results from point mutations. Mutations analysis of the kinase domain of ABL should be performed in case of failure to achieve or loss of a milestone. Mutations that result in resistance to the first line TKIs are characterised and mutational analysis serves as a guide to choose second line therapy. The T315I mutation imparts resistance to all TKIs except ponatinib.

The TKI treatment needs to be continued lifelong. Attempts to withdraw treatment in patients who have achieved prolonged deep molecular response have shown that the disease returns in a majority of the patients on discontinuation of treatment.

Allogenic stem cell transplant was the mainstay of treatment of CML before the introduction of TKIs. The availability of many TKIs has diminished the role of allogenic stem cell transplant. Allogenic stem cell transplant is indicated only in patients who progress on TKIs.

Prognosis

Introduction of imatinib altered the prognosis of CML by converting it form a progressive ad fatal disease to a chronic disease. The 8 year survival of CML on imatinib is 85%. Those progressing on imatinib can be treated with other TKIs.

 

by Avinash Deo

Dominant-Negative Phenotype


The human genome has two alleles of any gene. An allele may be dominant, recessive or co-domainant. Only one copy of an allele is needed for a dominant allele to express. A recessive allele expresses only when both the alleles are recessive.

The A and B blood group allele is dominant over the O group but are co-dominant with respect to each other. Individuals having genotype AA or AO express the A blood group antigen. Similarly individuals having genotype BB or BO express the B blood group antigen. An individual having genotype AB express both the blood group antigens. O is a recessive allele and only individuals with genotype OO have blood group O.

The biochemical basis of the ABH system is modification of the H antigen by enzymes encoded by the genes of blood group substances. Addition of N-acetylgalactosemine by the glycosyltransferase encoded by the allele encoding for A blood group converts the H antigen to A group antigen. Similarly the addition of galactose results in the synthesis of B group antigen. The allele for O group has a mutation and does not add any sugar.

Recessive genes are genes with mutations that result in loss of function. This is the case with the O blood group gene or with a thalassaemia gene. If recessive allele is present in the heterozygoyus state the product of the dominant allele, which encodes a functional protein, ensures there is synthesis of functional protein. The levels of encoded proteins in the presence of a mutant and recessive gene may be lower than in an individual without the mutant gene. Normal function is possible even with reduced levels of the encoded protein in almost all individuals and no disease occurs. This is the case with individuals with thalassaemia trait who have lower haemoglobin than normal individuals but this does not cause symptoms related to anaemia.

Some genes that encode for non-functional proteins manifest even when heterozygous with a functioning gene. These genes are known as dominant-negative. These genes usually encode for proteins that are dimers or multimers. The recessive gene has the ability to “poison” the components of the dimer/multimer produced by the normal genes and render them functionless.

Recessive genes encode for proteins that cannot form dimers/multimers. The product of these genes has no effect on the activity of the protein encoded by the normal allele. The levels of proteins may be reduced but all the protein synthesized by the dominant gene is functional. Usually the levels of proteins fall to half that in normal. This is almost always sufficient for normal function.

Dominant-Negative

Figure 1. The dominant negative phenotype

 

The dominant-negative genes have the capacity to form dimers/multimers and also also have the capacity to inhibit the function of the product of the normal gene (figure 1). A patient carrying a dominant-negative allele has reduced levels of functional proteins because of inhibition of function by the product of dominant negative allele. If one considers a patient who has a dominant negative mutation for a protein that is a homodimer, as is the case with factor XI, 75% of the factor XI synthesized will have the monomer produces by the dominant negative gene, Only 25% of the factor XI will be functional. This is consistant with the observation that these patients have factor XI levels between 20-30%. The situations in multimeric proteins and those proteins that are hetrodimers/hetromeltimers is more complex but the principle remains the same.