This document provides an overview of acute promyelocytic leukemia (APL). APL accounts for 5-8% of acute myeloid leukemia cases in younger patients. It is characterized by the presence of abnormal promyelocytes in the bone marrow and blood. APL represents a medical emergency due to a high risk of hemorrhage from disseminated intravascular coagulation. The diagnosis of APL is confirmed by identifying the characteristic t(15;17) translocation resulting in the PML-RARA fusion gene. Modern treatment with differentiation therapy has improved outcomes, with younger patients and those with lower white blood cell counts having a superior prognosis.

1. ACUTE PROMYELOCYTIC
LEUKEMIA
DR.MUNEERA GULL
2ND YEAR RESIDENT DEPARMENT
OF PATHOLOGY
SKIMS SOURA SRINAGAR

2. CONTENTS
 1.INTRODUCTION
 2.CLINICAL PRESENTATION
 3.PATHOLOGICAL FEATURES
 4.MORPHOLOGICAL SUBTYPES
 5.CYTOGENETICS
 6.LEUKEMOGENESIS
 7.DIAGNOSIS
 8.DIFFERENTIAL DIAGNOSIS

3. INTRODUCTION
 Acute promyelocytic leukemia is an acute myeloid leukemia in
which abnormal promyelocytes predominate
 Accounts for 5-8% of AML cases in younger patients with a lower
relative frequency in elderly patients
 Can occur at any age, but most patients are middle aged
 Annual incidence is 0.08 cases/lac pop

4.  Incidence does not vary by gender.
 APL can sometimes occur after cytotoxic therapy for another
disease (eg, breast cancer, lymphoma, other solid tumors),
especially in association with the use of topoisomerase-II inhibitors
such as etoposide and doxorubicin

5. CLINICAL PRESENTATION
APL represents a medical emergency with a high rate of early
mortality, often due to hemorrhage from a characteristic coagulopathy.
It is critical to start treatment with a differentiation agent (eg, all-trans
retinoic acid) without delay as soon as the diagnosis is suspected
based upon cytologic criteria, and even before definitive cytogenetic or
molecular confirmation of the diagnosis has been made

6. CLINICAL PRESENTATION
 — Patients with APL generally present with symptoms related to
complications of pancytopenia (ie, anemia, neutropenia, and
thrombocytopenia), including weakness and easy fatigability,
infections of variable severity, and/or hemorrhagic findings such as
gingival bleeding, ecchymoses, epistaxis, or menorrhagia.

7.  Unique to APL is a presentation with bleeding secondary to
disseminated intravascular coagulation.
 Disseminated intravascular coagulation (DIC) is frequently
present at diagnosis or occurs soon after the initiation of
cytotoxic chemotherapy in patients with APL. This
complication constitutes a medical emergency, since, if left
untreated, it can cause pulmonary or cerebrovascular
hemorrhage in up to 40 percent of patients and a 10 to 20
percent incidence of early hemorrhagic death . The risk
appears to be higher in patients with the microgranular
variant of APL

8.  The mechanism by which APL leads to DIC, which is often
accompanied by secondary fibrinolysis, is incompletely understood.
The following three factors may be of primary importance.
 Tissue factor, which forms a complex with factor VII to activate
factors X and IX.
 Cancer procoagulant, which activates factor X independent of factor
VII.
 Increased annexin II receptor expression on the surface of the
leukemic promyelocytes . Annexin II receptor binds plasminogen
and its activator, tissue plasminogen activator, increasing plasmin
formation by a factor of 60

9. PATHOLOGIC FEATURES
 APL is characterized by the presence of atypical
promyelocytes in the bone marrow and peripheral blood.
Promyelocytes are large (usually >20 microns in
diameter) myeloid precursors with variable morphology.
Often there is a high nucleus to cytoplasmic ratio, fine
chromatin, and prominent nucleoli.

10.  The cardinal feature of the promyelocyte is the presence
of many violet granules in the cytoplasm with either a
dense or coarse pattern, often obscuring the nucleus.
The cells of APL differ morphologically from those of
normal promyelocytes in that they are larger and
typically have creased, folded, bilobed, kidney-shaped,
or dumb-bell shaped nuclei

14. MORPHOLOGICAL
SUBTYPES
 1.Hypergranular(Classic M3):-
 (A) Nucleus…..folded, lobulated; granules obscure borders
 (B)Cytoplasm….prominent azurophilic granules
 (C)Auer rods…..frequent; faggot cells

15. Cont…
 2.Microgranular(M3V):-
 (A)Nucleus……..irregular folded
 (B)Cytoplasm….fine, small granules; dusky appearance
 (C)Auer rods……rare

16. • Hypergranular APL
 Prominent cytoplasmic granules
 Reniform/bilobed nucleus
 Multiple auer rods
• Microgranular APL
 Prominent leucocytosis
 Cytoplasmic granulation absent to
inconspicious
 Bilobed nuclei
 Auer rods rare

17. Cont…
 3.Promyelocytic Leukemia Hyperbasophilic:-
 (A)Nucleus…….high N:C ratio
 (B)Cytoplasm….granules sparse; strongly basophilic;
cytoplasmic budding
 (C)Auer rods…..not seen

19. Cont….
 4.Zinc Finger/Retinoic acid receptor-α(M3r):-
 (A)Nucleus…….regular round/ovoid:condensed chromatin pattern
 (B)Cytoplasm….granularity intermediate between hyper &
hypogranular
 (C)Auer rods…..rare; faggot cells absent

20. CYTOGENETICS & MOLECULAR
BIOLOGY
 Acute promyelocytic leukemia with t(15;17)(q24.1;q21.1);PML-
RARA is defined by the presence of a reciprocal translocation
between the long arms of chromosomes 15 and 17, with the
creation of a fusion gene, PML-RARA which links the retinoic acid
receptor alpha (RARA) gene on chromosome 17 with the
promyelocytic leukemia (PML) gene on chromosome 15

22.  Alternative fusion genes have been described that result in
leukemias that would now be classified as "AML with a variant
RARA translocation." This distinction has been made primarily
because patients with t(11;17) do not respond to therapy with
differentiation agents (eg, ATRA). The response of cases with other
fusion genes to differentiation therapy is varied. The most common
variant translocations are:

23. t(11;17)(q23;q21) — PLZF/RARa, often
CD13+, CD56+
t(5;17)(q35;q21) — NPM1/RARa, often CD13-,
CD56-
t(11;17)(q13;q21) — NuMA/RARa
T(17;17)(q11,q21)----STAT5b-RARα

24.  In addition to variant chromosome translocations in APL ,other
concurrent mutational events may also be seen
 Most frequent among these include Internal Tandem Duplication
(ITD) mutations of the fms like tyrosine kinase 3(FLT3) gene.
 Constitutive activation of the FLT3 receptor via this mutation is
known to confer a proliferative & survival advantage to the abnormal
cells

25. LEUKEMOGENESIS IN APL

27. DIAGNOSIS
 The diagnosis of APL is suspected by the characteristic morphology
of the leukemic cells, immunophenotype, or the presence of severe
coagulopathy. Another diagnostic clue is that the non-microgranular
form of APL often presents with leukopenia. The diagnosis is then
confirmed by the identification of the PML-RARA fusion gene or the
associated chromosomal translocation.

28.  1.CBC/PBF
 2.BMB with aspirate
 3.Metabolic profile for baseline renal and LFT
 4.Coagulation studies
 5.Cytochemistry(MPO,NSE)
 6.IMMUNOPHENOTYPE….APL with PML-RARA(hypergranular
variant) is characterised by low or absent expression of HLA-DR, CD34
& the leucocyte integrins CD11a, CD11b & CD18.

33.  It shows homogenous bright expression of CD33 & heterogenous
expression of CD13
 Most cases show expression of CD117
 Granulocytic differentiation markers CD15 & CD65 are negative
 In the microgranular morphology, there is frequently expression of
CD34 & CD2 atleast by some cells
 CD2 expression has been associated with FLT3 ITD

34.  10% APL cases epress CD56
 On immunocytochemistry, antibodies against the PML gene product
show a characteristic nuclear multigranular pattern with nucleolar
exclusion

36.  7.GENETIC STUDIES;
 The genetic abnormality may be detected using the following
techniques, each of which has advantages and disadvantages
 Conventional karyotype — This method is highly specific, and an
essential part of the standard workup, but it is time-consuming,
usually taking approximately two days for results.

37.  Fluorescence in situ hybridization — Fluorescence in situ
hybridization (FISH) for the PML/RARA fusion is less expensive and
quicker than conventional cytogenetics.
 FISH can be performed usually within 24 hours or, in some
instances, in an even shorter time.

38.  Reverse transcriptase polymerase chain reaction — Reverse
transcriptase polymerase chain reaction (RT-PCR) for PML-
RARA RNA is considered by many to be the current "gold
standard" method for confirming the diagnosis of APL. RT-
PCR also provides information on the PML breakpoint
location. However, RT-PCR has a long turn-around time
(approximately two days) and can have both false positives
(contamination artifacts) and false negatives (due to poor
RNA yield)

39.  Anti-PML monoclonal antibodies — Immunostaining with
anti-PML monoclonal antibodies is a somewhat specific test
that can be performed in as little as two to four hours . APL
demonstrates a microspeckled nuclear staining pattern with
nucleolar exclusion that differs from the discrete larger and
fewer nuclear dots seen in normal cells and other forms of
AML

41. DIFFERENTIAL DIAGNOSIS
 1.Reactive disorders of the bone marrow
 2. Other subtypes of acute leukemia
 3. Therapy with myeloid growth factors ,GCSF
 4.Chronic myelogenous leukemia
 5.FAB M2
 6. Monocytic leukemia

42.  Risk stratification:
 Sanz risk score.
 3 risk categories on the basis of TLC & Platelet count.
 Low risk is when TLC < 10 000/μl & platelet count > 40 000/μl.
98% 3 year relapse-free survival.
 Intermediate risk is when TLC < 10 000/μl & platelet count < 40
000/μl.
89% 3 year relapse free survival.
 High risk is when TLC > 10 000/μl.
70% 3 year relapse free survival.

43. PPROGNOSIS— Without treatment, APL is the most malignant form of AML
with a median survival of less than one month. However, with modern
therapy, APL is associated with the highest proportion of patients who are
presumably cured of their disease. Despite the overall good prognosis for
this group of patients, there is heterogeneity in this population. Patients
younger than age 30 years and those who present with a white blood cell
count less than 10 x 10 9 /L (10,000/microL) have superior event-free survival
. In contrast to other types of AML, age over 60 years is not a predictor of
poor results in APL

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