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 Table of Contents  
Year : 2022  |  Volume : 13  |  Issue : 1  |  Page : 63-67

Atypical morphology and aberrant immunophenotypic expression: A diagnostic dilemma in acute promyelocytic leukemia

Department of Pathology, AFMC, Pune, Maharashtra, India

Date of Submission04-Apr-2021
Date of Decision15-Jun-2021
Date of Acceptance17-Jul-2021
Date of Web Publication28-Apr-2022

Correspondence Address:
Dr. Shipra Verma
Department of Pathology, AFMC, Pune, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/joah.joah_42_21

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Acute promyelocytic leukemia (APL) is a subtype of acute myeloid leukemia, which is highly aggressive, yet the most curable. It is a medical emergency that requires a very high index of suspicion, as delay in the treatment could lead to fatality. The initial diagnosis is made on the basis of its typical clinical presentation, morphological and immunophenotypic features. However, definitive diagnosis rests on the cytogenetic study. We present one such interesting case of APL where the morphology as well as immunophenotypic features was quite deceiving, leading to a diagnostic dilemma.

Keywords: Acute myeloid leukemia, acute promyelocytic leukemia, cytogenetic, hyperbasophilic, promyelocytic leukemia protein-retinoic acid receptor alpha

How to cite this article:
Verma S, Singhal P, Singh S, Das S. Atypical morphology and aberrant immunophenotypic expression: A diagnostic dilemma in acute promyelocytic leukemia. J Appl Hematol 2022;13:63-7

How to cite this URL:
Verma S, Singhal P, Singh S, Das S. Atypical morphology and aberrant immunophenotypic expression: A diagnostic dilemma in acute promyelocytic leukemia. J Appl Hematol [serial online] 2022 [cited 2023 Sep 27];13:63-7. Available from: https://www.jahjournal.org/text.asp?2022/13/1/63/344264

  Introduction Top

Acute promyelocytic leukemia (APL) is a subtype of acute myeloid leukemia (AML). It forms 7%–8% of the adult AML cases with a median age of 47 years.[1],[2] It is one hematological malignancy which is a medical emergency. APL requires a prompt diagnosis based on its very characteristic clinical, morphological, immunophenotypic, and molecular features.[1],[3]

We present a rare and interesting case of APL, with quite deceiving morphology and aberrant immunophenotypic expression, posing a great deal of difficulty in the initial diagnosis. Owing to the aggressive nature of this malignancy, the diagnosis requires to be prompt and accurate. We need to be aware of the atypical present of this malignancy to get a clue and keep a high index of suspicion.

  Case Report Top

A 26-year-old female, known case of polycystic ovarian disease, admitted to a tertiary care hospital with complaints of easy fatigability for 2 weeks, low-grade intermittent fever, headache and shortness of breath of the same duration. There was a history of one episode of bleeding from the gums.

On examination, the patient was afebrile with pallor, ecchymotic patches over her right shoulder and left iliac crest. Abdominal examination showed an enlarged liver 3 cm below the costal margin. Imaging studies revealed hepatomegaly with a liver span of 16.5 cm, edematous and thickened gall bladder wall. Noncontrast computed tomography of the head showed a normal study.

Hemogram revealed severe anemia with hemoglobin of 4.4 g/dL, total leukocyte count (TLC) of 2900/μL, and platelet count of <10,000/μL. The prothrombin time activated partial thromboplastin time and fibrinogen levels were normal.

Peripheral blood study [Figure 1] showed a differential count of neutrophils 2%, lymphocytes 28%, monocytes 8%, and atypical cells 62%. These atypical cells were intermediate to large size with high nuclear-to-cytoplasmic ratio, deeply basophilic cytoplasm with prominent projections. Nuclei were reniform with open chromatin and 1–2 prominent nucleoli. There were no cytoplasmic granules or Auer rods. These blasts were strongly positive for myeloperoxidase staining (MPO) [Figure 1]d. In view of maturation arrest and cytochemistry results, a suspicion of APL was kept in mind, although the morphology was not supportive of this diagnosis.
Figure 1: Peripheral blood. (a) Circulating blasts show basophilic cytoplasm, prominent projections on the cell membrane (Leishman stain, ×400). (b and c) Nuclear membrane is irregular with open nuclear chromatin, 1-2 prominent nucleoli. No Auer rods were seen (Leishman stain, ×1000). (d) Blasts were strongly positive for myeloperoxidase (myeloperoxidase stain, ×1000)

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The bone marrow study revealed a hemodiluted aspirate. The bone marrow biopsy [Figure 2] was hypercellular with suppression of all three cell lineages due to the replacement of the marrow by immature cells. These immature cells showed positivity for CD34, CD117 and MPO, focal positivity for CD11c and NSE. A diagnosis of acute myeloid leukemia (MPO positive) was made.
Figure 2: Bone marrow biopsy. H and E (a) ×40, (b) ×100, (c) ×400, Core biopsy showed nearly 100% marrow cellularity with replacement of the marrow spaces by monomorphous population of immature blast cells. (d-f) ×200, Blasts were positive for myeloperoxidase, CD117 and CD34 respectively

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The flow cytometric analysis [Figure 3]a revealed atypical cells/blasts that were positive for CD34 and HLA-DR. CD117, CD13, CD33, and MPO were expressed by these cells. CD64 and CD19 were expressed in a subset of cells. The monocytic markers (CD11c and CD14) and granulocytic marker (CD15) were negative. The flow cytometric diagnosis was consistent with AML with aberrant CD19 expression. Based on these, the patient was started on chemotherapy.
Figure 3: (a) Immunophenotypic features by flow cytometric analysis revealed CD45 dim population of atypical blasts which were predominantly positive for CD13, CD33, CD117 and Myeloperoxidase. CD34 and HLA-DR were also positive in majority of the blasts, CD19 and CD64 were positive in a subset of blast cells. (b) Karyotype report showing chromosomal translocation t (15;17) (q24.1;q21.2)

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Subsequently, after 48 h of initial workup, the cytogenetic study showed translocation t (15; 17) (q24.1;21.2) [Figure 3]b and quantitative RT-PCR revealed promyelocytic leukemia protein-retinoic acid receptor alpha (PML-RARα) (bcr-1 transcript) fusion gene that established the diagnosis of APL. The patient was switched on to all-trans retinoic acid (ATRA) (45 mg/m2/day) and arsenic trioxide (0.15 mg/kg/day) along with dexamethasone and component support. Following this, the patient showed clinical improvement along with clearance of blasts, increase in TLC and differentiation in the neutrophilic series on the follow-up peripheral blood studies.

  Discussion Top

APL is classified morphologically as AML-M3 by French-American-British classification. While it is classified under AML with recurrent genetic abnormalities by the World Health Organization (WHO), 2016 classification.[1],[3] It generally presents with pancytopenia and coagulopathy in young adults. It is characterized by the proliferation of abnormal promyelocytes in the bone marrow.[4],[5]

Morphologically, APL is classified into four types. The major type being the classical or hypergranular variant (Classical M3) with heavily granulated cells and frequent Auer rods, Faggot cells. The nuclei are folded and almost obscured by the granules. The other type is hypogranular or microgranular variant (M3V) with fine granules, that are not appreciable on light microscopy. It has a dusky appearance with irregular, folded nucleus, Auer rods are rarely seen. The third morphological form, very uncommon, is a hyperbasophilic variant, with very few granules, if any, deeply basophilic cytoplasm with blebs or projections on the surface. Cells have a high nucleocytoplasmic ratio with irregular nuclear borders. There is a lack of Auer rods in this variant. Last one is another rare variant with promyelocytic leukemia zinc finger/RARα fusion product (M3r) that has round, regular nuclei, they lack of granules and Auer rods.[1],[5],[6]

On immunophenotyping, APL cells generally lack HLA-DR and CD34, while they express myeloid markers CD33, CD13. They are negative for T-cell markers (CD7) and myelomonocytic markers (CD11b, CD14). Aberrant expression of CD2, CD19, and CD34 is correlated with the M3V form. CD56 expression is known to be associated with poor prognosis.[1],[7],[8]

In a case report by McDonnell et al., they found circulating blasts with lacy chromatin, scant blue cytoplasm, no Auer rods, a few showing granules. In their case, they found only a few blasts with folded nucleus as was found in the present study. Their flow cytometric analysis showed aberrant expressions of CD34, CD2, dim HLA-DR. Similarly, aberrant expression of CD34 and HLA-DR was seen in the present study. The diagnosis in this case too rested on cytogenetic study.[2]

In another case report by Bajaj et al., they found blasts with hyperbasophilic cytoplasm, blebs with lack of Auer rods, which was in conjunction with the findings of the present case, but they found numerous small granules in the cytoplasm, contrary to our case where only a few blasts showed scant granules. The report by Bajaj et al. does not mention the findings on immunohistochemistry or flow cytometry.[6]

A report by Mohamed et al., mentions M1 like blasts in the aspirate with no Auer rods and mostly agranular blasts. No abnormal promyelocytes were noted, similar to the present study, although the morphology of blasts in our case was that of hyperbasophilic variant. The flow cytometry in this case showed cells with low side scatter, expressing CD13, CD33, CD117, and MPO. CD15, CD11c, and CD14 were negative. They found aberrant expression of CD34 and HLA-DR as was found in the present case.[9] Similar flow cytometric findings with aberrant CD34 positivity were seen in one of the three cases in a case series by Wang et al.[7]

APL is associated with life-threatening coagulopathy and has had a poor prognosis with a high death rate, although our patient normal coagulation profile. However, in the last two decades, there has been a paradigm shift with the advent of the use of ATRA in the form of targeted therapy for APL. It has transformed APL into the most curable leukemia with a favorable outcome.[5],[10]

Early and accurate diagnosis of APL is of utmost importance for an early intervention to prevent the dreaded complications of coagulopathy. The initial diagnosis is completely based on the morphology of cells and cytochemistry. Thus, along with the common morphological types, the rare variants should always be kept in mind. Hyperbasophilic variant is an extremely rare variant of this rare disease. The immunophenotyping by flow cytometry is instrumental in rapid diagnosis, but aberrant expression may be present which is misleading, as in the present case. Testing by cytogenetics, fluorescence in situ hybridization and reverse transcriptase polymerase chain reaction for PML-RARα are the only confirmatory tests.

Our patient did not have the characteristic morphological picture, flow cytometry or immunohistochemical findings to suspect APL. This case report highlights the importance of a high index of suspicion of APL. Although definitive diagnosis can be made only by cytogenetics or molecular studies, the atypical morphological appearances and aberrant immunophenotypic expressions, as in our case, need to be kept in mind by a pathologist for correctly and timely diagnosing this highly curable malignancy which could otherwise be devastating, claiming a young life.

  Conclusion Top

APL is a highly aggressive form of AML which can present as medical emergency. It requires a very high index of suspicion, as delay in the treatment could lead to fatality. This case report highlights the importance of this entity and its variants.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Soignet S, Maslak P, Lancet JE. Acute promyelocytic leukemia. In: Greer J, editor. Wintrobe's Clinical Hematology. 14th ed. USA: Lipincot Williams and Wilkins, Wolter- Kluwer Business; 2014. p. 5187-245.  Back to cited text no. 1
McDonnell MH, Smith ET Jr., Lipford EH, Gerber JM, Grunwald MR. Microgranular acute promyelocytic leukemia presenting with leukopenia and an unusual immunophenotype. Hematol Oncol Stem Cell Ther 2017;10:35-8.  Back to cited text no. 2
Arber A, Brunning R, Le Beau M, Falini B, Vardiman JW, Porwit A, et al. Acute myeloid leukaemia with recurrent genetic abnormalities. In: Swerdlow SH, editor. WHO Classification of Tumors of Hematopoietic and Lymphoid Tissues. 4th ed. Lyon, France: IARC; 2017. p. 130-49.  Back to cited text no. 3
Akhtar K, Ahmad S, Sherwani RK. Acute promyelocytic leukemia, hypogranular variant: A rare presentation. Clin Pract 2011;1:18-9.  Back to cited text no. 4
Thomas X. Acute promyelocytic leukemia: A history over 60 years-from the most malignant to the most curable form of acute leukemia. Oncol Ther 2019;7:33-65.  Back to cited text no. 5
Bajaj P, Devangana R, Shah BS, Kaur A. Hyperbasophilic variant of acute promyelocytic leukemia. MVP J Med Sci 2016;3:125-7.  Back to cited text no. 6
Wang X, Wang J, Zhang L. Characterization of atypical acute promyelocytic leukaemia: Three cases report and literature review. Medicine (Baltimore) 2019;98:1-7.  Back to cited text no. 7
Dong HY, Kung JX, Bhardwaj V, McGill J. Flow cytometry rapidly identifies all acute promyelocytic leukemias with high specificity independent of underlying cytogenetic abnormalities. Am J Clin Pathol 2011;135:76-84.  Back to cited text no. 8
Mohamed M, Dun K, Grabek J. Atypical features in a patient with acute promyelocytic leukaemia: A potential diagnostic pitfall. BMJ Case Rep 2013;2013:1-5.  Back to cited text no. 9
Wang ZY, Chen Z. Acute promyelocytic leukemia: From highly fatal to highly curable. Blood 2008;111:2505-15.  Back to cited text no. 10


  [Figure 1], [Figure 2], [Figure 3]

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