1  Chapter  29  –  Introduction  to  Leukocyte  

Neoplasms    General  Characteristics  of  Leukocyte  Neoplasm  

Most  malignancies   of   the  hematopoietic  system  are  acquired  genetic  disease  

Most   leukocyte   malignancies   are   not  localized  but  rather  are  systematic  at  the  initiation  of  the  malignant  process  

 Etiology  of  Leukocyte  Neoplasm  

Environmental  toxins  can  induce  genetic  changes  leading  to  malignant  phenotype  such  as:  

a) Radiation  exposure    b) Exposure   to   organic   solvents  

such  as  benzene   Two   types   of   lymphoid  malignancies   in  

which  virus  play  a  pathogenic  role  a) Epstein-­‐Barr  virus  

! Development   of   Burkitt   non-­‐Hodgkin  lymphoma  

b) T-­‐cell   lymphotropic   virus   type   1  (HTLV1)  ! Cause  of  adult  T-­‐cell  leukemia  

/  lymphoma    Classification  Schemes  for  Leukocyte  Neoplasm  

The   French-­‐   American   –British   (FAB)  schemas   (1970’s   and   1980’s)   were  based   largely   on   morphologic  characteristics   and   relied   heavily   on  examination   of   routine   histologic   stain  preparations   to   distinguish   lymphoid  neoplasms  from  myeloid  neoplasms  ! Lymphoblasts:  

a) 2-­‐3   times   the   diameter   of  lymphocytes  

b) Scant  blue  cytoplasm  c) Uniform  coarse  chromatin  d) Inconspicuous  nucleoli  

! Myeloblasts:  a) 3-­‐5   times   the   diameter   of  

lymphocytes  b) Moderate  gray  cytoplasm  c) Uniform  fine  chromatin  d) 2  or  more  prominent  nucleoli  e) Possible  Aüer  rods  

Modern   pathologist   moved   to   a   more  precise  classification  based  on  recurring  chromosomal   and   genetic   lesions   found  in  many  patient    

These   lesions   are   related   to  disruptions  of   oncogenes,   tumor   suppressor   genes  and   other   regulatory   elements   that  control   proliferation,   maturation,  apoptosis  and  other  vital  cell  functions  

WHO  new  classification  scheme  (2001)  ! For   acute   myeloid   leukemias  

(AMLs)  there  are  some  remnants  of  the  old  FAB  classification  

! New   classifications   were  introduced   for   leukemias  associated   with   consistently  recurring   chromosomal  translocation  

 Chromosomal  Abnormalities  in  Hematologic  Neoplasm  

The   first   two   genetic   lesions   found   in  any   kind   of   human   cancer   were  identified   as   chromosomal  translocations   occurring   in   leukocyte  malignancies  which  were:  

! t(9;22)   translocation   in   chronic  myelogenous  leukemia  (CML)  

! t(8;14)   translocation   in   Burkitt  lymphoma  

 Oncogenes  

Oncogenes:  ! Old   definition:   Identified   as   genes  

that   carried   rapidly   transforming  retroviruses   derived   from   normal  cellular   homologues,   proto-­‐oncogenes  

! New   definition:   Genes   that   cause  dominant   acting   cancer   mutations,  regardless   of   whether   they   are  derived  from  a  retro  virus  

The   dominant   transforming   oncogenes  is   able   to   alter   the   gene   product   and  transform   the   cell   into   a   malignant  phenotype  

CML   and   Burkitt   lymphoma,   involve  oncogenes   that   are   activated   when  

  2  brought   into   proximity   with   their   new  partners  on  fusion  genes  

! CML:  ABL   proto-­‐oncogene   on  chromosome  9   is  activated  when  fused   to   the   BCR   component   of  chromosome  22  

! Burkitt  lymphoma:  MYC   proto-­‐oncogene  chromosome   8   is   fused   with   the  immunoglobulin   heavy   chain  locus  on  chromosome  14  

 Tumor  Suppressor  Genes  

They   code   for   proteins   that   resist  malignant  transformation  

Two  hot  mechanism  of  Knodson:  Cells   are   transformed   into   a   malignant  phenotype   only   after   both   alleles   of  these  genes  have  been  lost  or  inactivated    

Autosomal   dominant   familial   cancer  predisposition  syndromes:  

! RB1   tumor   suppressor   gene                              in  familial  retinoblastoma  

! TP53  gene                                                                                              in  Li-­‐Fraumeni  syndrome  

! WT1  gene  in  Wilms  tumor  

! NF1  gene  in   familial   neurofibromatosis  type  1  

 Other  Genetic  Changes  

Beyond   oncogenes   and   tumor  suppressor   genes   other   genes   are  involved  in  DNA  repair  mechanism  

Mutation   in   these   genes   lead   to   genetic  instability  and  increased  mutation  rates    

Examples  are:  ! DNA   mismatch   repair   genes  

MLH1  and  MLH2  ! Fanconi  anemia  gene  FA  which  is  

important   for   maintaining  genomic   stability   in  hematopoietic  tissues  

     

Molecular  Pathways  Perturbed  by  Cellular  Transformation    ! Blocked  differentiation  ! Transcriptional  repression  ! Disruption  of  cell  signaling    ! Progression  ! Apoptosis    

~Blocked  differentiation~   t(15;17))   translocation   found   in   APL  

which   fuses   the   PML   gene   to   the   RARA  (retinoic   acid   receptor   alpha)   gene,  clearly   results   in   a   state   of   arrested  differentiation   because   the   RARA-­‐induced  differentiation  is  inhibited  

Treating   patients   with   APL   with  pharmacologically  high  doses  of  all  trans  retinoic   acid   can   overcome   this   block  and  permit  APL  cells  to  differentiate  into  normal   neutrophils   thus   APL   lose   their  leukemic  potential  

 ~Transcriptional  repression  and  

condensational  abnormalities  in  the  chromatin~  

Chromosomal   translocation   involving  BCL6  gene  ! BCL6   encodes   for   a   transcriptional  

receptor   responsible   for   recruiting  the   histone   deacetylase   complex,  which   regulates   germinal   center  formation  in  lymph  nodes    

! The   mutation   of   BCL6   leads   to  excessively  repressed  DNA  which   in  this  case  prevents  lymphocytes  from  progressing  beyond  germinal  center  stage  of  development  

 ~Disruption  of  cell  signaling~  

Often   by   way   of   activation   of   kinase  cascades  

FLT3   codes   for   a   tyrosine   kinase  receptor   preferentially   expressed   on  hematopoietic   stem   cell   that   mediates  proliferation  and  differentiation    

A   unique   mutation   resulting   in   the  internal   tandem   duplication   leads   to  constitutional  activation  of  this  pathway  

  3  in   many   forms   of   AML   and   other  hematopoietic  malignancies  

 ~Progression~  

Many   cyclin   dependent   kinase   are  altered  in  lymphoid  malignancies    

The   cyclin   dependent   kinase   tightly  regulate   cell   cycle   progression   through  synthesis,   proteolysis,   and  phosphorylation  of  cyclins  

 ~Apoptosis~  

Vital  process  that  organisms  to  eliminate  redundant,   damaged,   aged   or   infected  cells  

Apoptosis   is   essential   to   contain   and  control   the  massive  expansions   that   the  hematopoietic   system   is   capable   of  generating  at   time  of   stress   infection  or  hemorrhage    

Caspases   are   a   family   of   proteases   that  participate   in   the   apoptotic   cascade  triggered   in   response   to   proapoptotic  signals  

 Therapy  for  Leukocyte  Neoplasm  

Forms   of   therapy   for   leukocyte  neoplasm:  

a) Chemotherapy  b) Radiation  therapy  c) Supportive  therapy  d) Targeted  therapy    e) Stem  cell  transplantation  

Curative   treatment   strategies   are   a  realistic  goal  for  patients  with:  

a) Hodgkin  lymphoma  b) CML  c) Hairy  cell  leukemia  d) Some   forms   of   non-­‐Hodgkin  

lymphoma  e) Children   with   acute  

lymphoblastic  leukemia    Chemotherapy  

Chemotherapy   is   oral   or   parenteral  cancer   treatment   with   compounds   that  possess  antitumor  properties  

   

Classification  or  chemotherapy  agents:  a) Effect  on  cell  cycle    b) Biochemical  mechanism  of  action  

Effect  on  cell  cycle  ! Phase   specific:   affect   cells   in   a  

specific  phase  of  the  cell  cycle  ! Phase   nonspecific:   affect   cells  

regardless  of  the  phase  in  the  cell  cycle  

! Cycle   specific:   kills   cell   that   are  moving   within   the   cell   cycle  regardless  of  the  phase  of  the  cell  cycle  

! Cycle   nonspecific:   kills   non  dividing   cells   or   cells   in   the  resting  state  

Chemotherapeutic   agents   affect   both  neoplastic  and  normal  cells  

Chemotherapy   agents   are   categorized  as:  

Alkylating  agents  Mechanism   of  action  

! Ionize   within   cells   forming   highly  reactive   free   radicals   that   damage  DNA    

! Act  on  any  phase  of  the  cell  cycle  Examples   Nitrogen  mustard   Busulfan  

Cyclophosphamide   Melphalan  Chlorambucil    Plant  alkaloids  

Mechanism   of  action  

! Affect   microtubules   and   interrupt  the   process   of   mitotic   spindle  formation  during  metaphase  

Examples   Vincristine   Vinblastine  Antitumor  antibodies  

Mechanism   of  action  

! Inhibit  the  synthesis  of  RNA  or  DNA  and   interfere   with   the   G2   phase   of  the  cell  cycle  

Examples   Daunorubicin   Doxorubicin  Antimetabolites  

Mechanism   of  action  

! Interfere  with  the  normal  function  of  various  essential  metabolites  

Examples   Methotrexate   Purine  analogues  ! 6  mercaptopurine  ! 6   thioguanine  

(Affect  s-­‐phase)  Folate  antagonists  Glucocorticoids  

Mechanism   of  action  

! Have  a  lympholytic  effect  ! Affect   nonproliferating   cells   and  

those  in  cycle  ! Protein   synthesis   and   mitosis   may  

be  inhibited  Examples   Hydrocortisone   Dexamethasone  

Prednisone   Prednisolone    

  4  Radiation  therapy  

Radiation   kills   cell   by   producing  unstable  ions  that  damage  DNA  and  may  cause  instant  or  delayed  death  of  the  cell  

Hematopoietic   system,   gastrointestinal  tract  and  the  skin  are  most  often  affected  during  radiotherapy  

The   toxic   effect   is   usually   reversible  when  radiation  is  stopped  

 Supportive  therapy  

Substances   produced   by   the   body   that  are   now   created   by   the   lab   and   cleared  FDA   for   general   use   in   the   supportive  care   of   cancer   patients   particularly  patients  with  hematologic  malignancies  

 Targeted  therapy  

Therapies  that  target  specific  tumor  cells  and  leave  normal  cells  untouched  

 Stem  cell  transplantation  

Stem   cell   transplantation   is   a   process  that   has   replaced   or   modernized   bone  marrow  transplantation  

Sources   usually   come   from   bone  marrow,  peripheral  blood  and  umbilical  cord  blood    

Regardless   of   the   source   all  hematopoietic  stem  cells  are  called  adult  stem  cells  

Three  general  types  of  donor:  a) Identical   twin   (syngeneic  

transplant)   –   most   desirable   but  very  rare  

b) Donor   genetically   different   from  the   recipient   (allogeneic  transplant)  

c) Patients   own   marrow   or  peripheral   blood   stem   cell    (autologous  transplant)  

 Allogeneic  transplantation  

Most   stem   cells   are   different   from   the  recipient   thus   the   intent   is   to  match   as  many  HLA  as  possible    

Major   complication   is   the   immunogenic  reaction   of   donor   T   cells   against   the  

tissues   of   the   recipient   resulting   to  graft  versus  host  disease  (GVHD)  

Two  forms  of  GVHD  ! Acute  GVHD  

• Develops   immediate   after  transplantation  or  short  after  

• Characterized  by  skin   rash   liver  dysfunction  diarrhea  

! Chronic  GVHD  • Develops   more   than   100   days  

after  transplantation  • Characterized   by   multisystem  

autoimmune   disease,   skin  lesions,   joint   contractures,  chronic  hepatitis,  malabsorption  and   chronic   obstructive  pulmonary  disease  

 Autologous  transplantation  

Cells  are  harvested  from  the  patient  and  after  conditioning  are  transplanted  back  

Malignant   cells   are   purged   in   vitro  through   the   use   of   antileukemic  monoclonal   antibodies   or   cytotoxic  drugs  

 Comparison  of  autologous  transplantation  with  matched  allogeneic  transplantation  

a) Although  allogenic  transplantation  is  not  available  to  every  patients,  almost  every  patient   is   eligible   for   autologous  transplantation  

b) Post   transplantation   morbidity   and  morbidity   are   lower,   hospital   stays   are  shorter   for   autologous   transplantation  recipients  

c) Relapse   rate   is   higher   among   recipients  of  autologous  transplants  

 Deaths   after   transplantation   are   most   likely  caused  by:  

a) Complications   of   conditioning   such   as  infections   or   bleeding   from   bone  marrow  suppression  

b) Complications  of  GVHD  c) Relapse  (regrowth  of  malignant  cells  d) Failure  of  donor  to  engraft