Case 4 - Discussion

Uploaded: 2007-06-07, Updated: 2008-01-02

PERIPHERAL BLOOD        

Examination of Wright-Giemsa stain peripheral blood smears reveals pancytopenia. An abnormal population of cells with large irregular folded nuclei, scant to moderate cytoplasm is identified at 20%. Some of the abnormal cells contain azurophilic granules.

BONE MARROW CORE BIOPSY AND CLOT SECTION:

The bone marrow is hypercellular (100%) and diffusely replaced by sheets of immature myeloid cells with kidney-shaped, bilobed and very irregular nuclear contour and abundant pink cytoplasm. Occasional mitotic figures and apoptotic bodies are noted. Minimal erythropoiesis and megakaryopoiesis is present. Occasional neutrophils are present. Marked diffuse fibrosis(3+/3+) is identified by reticulin stain . Stainable iron is markedly decreased.     

BONE MARROW ASPIRATE SMEAR AND TOUCH IMPRINTS:

The bone marrow smear is hypercellular with spicules. The M:E ratio is 15:1. Markedly increased blasts/promyelocytes are noted (estimated at 78%). The morphology of the promyelocytes exhibits great variability. The nuclei range from round to kidney-shaped to flower-shaped. Some of promyelocytes have scant amount of cytoplasm, some have abundant cytoplasm with packed azurophilic granules. Occasional auer rods are noted. Erythropoiesis is markedly reduced with unremarkable morphology. Occasional small mature lymphocytes are present. Markedly decreased iron storage is noted on iron stain.

Bone marrow: INTERPRETATION:
An aberrant population expressing dim CD45, CD13, CD33, CD117, CD71, CD38 and dim CD11b is identified at 88% of the total events (without debris). These aberrant cells are negative for CD34, HLA-DR, CD14 and CD15. The immunophenotype is consistent with acute promyelocytic leukemia.

Total events 		H gate Dim 		A gate Bright CD45
analyzed = 48568	CD45+ events = 38061    Positive events =1158
			(88% of total)		(3% of total)
     
  CD45+/CD14-		 97%			  100%
  Total CD14+		  3%
  Total CD13+		 99%
  CD34+/CD13+		 <2%
  Total CD15+		  4%
  CD34+/CD15+		 <2%
  Total CD33+		 99%
  CD34+/CD33+		 <2%
  Total CD34+		 <2%
  Total CD11b+		 87%
  Total CD41+		  4%
  Total CD71+		 96%
  CD34+/CD71+		 <2%
  Total CD117+		 98%
  CD34+/CD117+		 <2%
  Total HLA DR+		 <2%
  CD34+/HLA DR+		 <2%
  Total CD38+		100%			  73%

CYTOGENETICS (UNMC, Cytogenetics)

NTERPRETATION:
Cytogenetic analysis revealed the presence of an abnormal clone characterized by a reciprocal translocation involving 15q and 17q. The t(15;17) is diagnostic for the M3 type of AML.

NOMENCLATURE: 46,XY,t(15;17)(q22;q11.2)[14]/46,XY[6]

Acute promyelocytic leukemia, Hypergranular Type

CLINICAL FEATURES

• An acute leukemia with predominant abnormal promyelocytes, 5-8% of AML;

• Age: all age, but most in mid-life;

• Clinical features: a clinical emergency due to frequent association with DIC.

MICROSCOPIC FINDINGS

• Variable nuclear size and shape, often kidney-shaped or bilobed / butterfly shape;

• In most cases, myeloblasts are a minor component and rarely > 20%;

• Hypergranular APL

  • Peripheral leukocyte count is usually decreased;

  • Cytoplasm is often filled with densely packed or coalescent large, bright pink, red or purple granules;

  • In some cases, the cytoplasm is filled with fine dust-like granules;

  • Auer rods:  in 90% cases, can be multiple, numerous and intertwined;

  • Faggot cell: cell with bundles of Auer rods;

• Hypogranular/microgranular APL

  • Peripheral leukocyte count is elevated or markedly elevated due to a rapid doubling time;

  • Cytoplasm has a paucity or absence of fine granules, and nuclei are predominantly bilobed;

  • Scant Auer rods may be identified.

SUBTYPES OR VARIANTS

• APL with t(11;17)(q23;q21), PLZF-RARA fusion gene; regular nuclei, many granules, no Auer rods, increased pseudo Pelger-Huet cells; resistent to ATRA;

• APL with t(11;17)(q13;q21), NuMA-RARA fusion gene

• APL with t(5;17)(q32;q12), NPM-RARA fusion gene. Responsive to ATRA.

DIFFERENTIAL DIAGNOSES

IMMUNOHISTOCHEMISTRY AND SPECIAL STAINS

• Markedly increased orthogonal (side) scatter

• Positive: CD33, CD13, MPO

• Frequent coexpression of CD2 and CD9

• Negative: HLA-DR, CD34, CD15

• NSE weakly positive in 25% cases

ELECTRON MICROSCOPIC FINDINGS

• Auer rods: hexagonal arrangement of tubular structures with a specific periodicity of about 250nm.

CYTOGENETIC STUDIES

• t(15;17)(q22;q12), 98% cases, PML-RARα fusion protein.

• t(11;17)(q23;q21), PLZF-RARA fusion gene.

• t(11;17)(q13;q21), NuMA-RARA fusion gene.

• t(5;17)(q32;q12), NPM-RARA fusion gene

TREATMENT AND PROGNOSIS

• Both hypergranular and hypogranular APLs have the same characteristic ultrastructural, cytogenetic, molecular and clinical features and both response to treatment with ATRA. They defer mainly in the peripheral blood count, the size and number of the visible granules and the prominence of the abnormal nuclear shape.

• Particularly sensitive to treatment with all trans-retinoic acid that acts as a differentiating agent.

• Favorable prognosis when treated with all trans-retinoic acid and an anthracycline.

REFERENCES

• Jaffe ES, Harris NL, Stein H, Vardiman JW, editors. Pathology and genetics of tumours of haematopoietic and lymphoid tissues. World Health Organization classification of tumours. Lyon (France): IARC Press; 2001.