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European APL platform

A Challenging Diagnosis

A 78-year-old male came to the emergency room for history of fatigue and swelling and pain of the lower left limb. Patient medical history disclosed hypertension in pharmacological therapy and thyroiditis.

14th May 2017

History

A 78-year-old male came to the emergency room for history of fatigue and swelling and pain of the lower left limb. Patient medical history disclosed hypertension in pharmacological therapy and thyroiditis.

Initial evaluation

At initial evaluation, skin examination revealed diffuse petechiae on the lower extremities, but also swelling and redness of the left ankle and foot. A Doppler ultrasound exam was performed and disclosed deep vein thrombosis of the popliteal vein was detected. 

Laboratory results

CBC, coagulation, and biochemistry tests were ordered and are shown in Table 1 below.

Table 1
Parameter Value
Hb 10 g/L
Platelets30×109/L
WBC24×109/L
INR1.3
PT20.7
APTT20.4
Fibrinogen1.9 g/L
D-dimer16000 ng/mL
ATIII75%
AST30 g/L
ALT40
Creatinine1.6 mg/dL
LDH150
Total bilirubin2.5

The complete blood count with differential revealed leucocytosis, anemia, and thrombocytopenia. In addition the D-dimers were significantly increased.

Bone marrow and cytogenetic observations

Urgent hematology consultation was requested and bone marrow examination was performed and morphologic examination showed infiltration by granulated blasts without Auer rods and round nuclei. Immunophenotypic analysis disclosed a population of myeloid blasts positive for CD33, CD13, CD117, MPO and CD56 and negative for CD34 and HLA-DR. Given the laboratory picture suggestive of APL, the hematology consultant started therapy with all-trans retinoic acid (ATRA) and genetic studies to confirm the presence of PML/RARA were initiated. However, indirect immunofluorescence with PGM3 (anti-PML) antibody showed a nuclear body pattern (negative for PML/RARA) and RT-PCR tested negative for PML/RARA1–2.

Therefore, cytogenetic analysis and molecular biology were carried out in order to further investigate the case. Results of genetic studies are shown in Figure 2 below.

Figure 2. Cytogenetic analysis showing t(11;17)(q23;q21).

Karyotype showed the presence of a reciprocal balanced translocation between chromosome 11 and 17 t(11;17)(q23;q21) [15]. Given the suspect of APL, molecular biology for ZTBTB16-RARA rearrangement was performed and resulted positive and a diagnosis of APL haboring a variant RARA rearrangement was established3.

Education comment

In approximately 1-2% of APL cases, the RARA gene on chromosome 17 is involved but the PML gene on chromosome 15 is not. Interestingly, all these variants contain the exact same RARA sequence as all the translocations breakpoints map in the second intron of the RARA gene3. To date, more than 10  variant translocations have been identified, including ZBTB16/RARA (formerly named ZBTB16-RARA), NPM/RARA, NuMA/RARA, STAT5B/RARA, PRKAR1A/RARA, BCOR/RARA, FIP1L1/RARA, OBFC2A/RARA, GTF2I/RARA and the most recent IRF2BP2/RARA and FNDC3B/RARA3456,789. The identification of these variants is important because they display different sensitivities to APL specific therapy, in particular all-trans retinoic acid (ATRA) and arsenic trioxide (ATO).

The most common APL variant is t(11;17)(q23;q21) which fuses ZBTB16 (formerly ZBTB16 or promyelocytic leukemia zinc finger) with RARA and resulting in the production of the ZBTB16-RARA fusion protein. These cases are characterized by blasts with regular nuclei, and morphologic features intermediate between FAB M2 and FAB M3 subtypes. As in our case, the ZBTB16-RARA t(11;17) APL variant is also immunophenotypically very similar to APL and commonly associated with CD56 expression. At the clinical level, ZBTB-RARA rearrangement show in vitro and in vivo no sensitivity to ATRA and ATO. 3 However, occasional case reports of patients achieving differentiation of leukemic blasts with the employment of ATRA in combination with other agents.10,11

References

  1. Falini B, Flenghi L, Fagioli M, et al. Immunocytochemical diagnosis of acute promyelocytic leukemia (M3) with the monoclonal antibody PG-M3 (anti-PML). Blood. 1997;90(10):4046–4053.
  2. van Dongen JJ, Macintyre EA, Gabert JA, et al. Standardized RT-PCR analysis of fusion gene transcripts from chromosome aberrations in acute leukemia for detection of minimal residual disease. Report of the BIOMED-1 Concerted Action: investigation of minimal residual disease in acute leukemia. Leukemia. 1999;13(12):1901–1928.
  3. Grimwade D, Biondi A, Mozziconacci MJ, et al. Characterization of acute promyelocytic leukemia cases lacking the classic t(15;17): results of the European Working Party. Groupe Francais de Cytogenetique Hematologique, Groupe de Francais d’Hematologie Cellulaire, UK Cancer Cytogenetics Group and BIOME. Blood. 2000;96(4):1297–1308.
  4. Yamamoto Y, Tsuzuki S, Tsuzuki M, et al. BCOR as a novel fusion partner of retinoic acid receptor alpha in a t(X;17)(p11;q12) variant of acute promyelocytic leukemia. Blood. 2010;116(20):4274–4283.
  5. Catalano A, Dawson MA, Somana K, et al. Brief report: The PRKAR1A gene is fused to RARA in a new variant acute promyelocytic leukemia. Blood. 2007;110(12):4073–4076.
  6. Won D, Shin SY, Park CJ, et al. OBFC2A/RARA: a novel fusion gene in variant acute promyelocytic leukemia. Blood. 2013;121(8):1432–1435.
  7. De Braekeleer E, Douet-Guilbert N, De Braekeleer M. RARA fusion genes in acute promyelocytic leukemia: a review. Expert Rev. Hematol. 2014;7(3):347–57.
  8. Jovanovic J V, Chillon MC, Vincent-Fabert C, et al. The cryptic IRF2BP2-RARA fusion transforms hematopoietic stem/progenitor cells and induces retinoid-sensitive acute promyelocytic leukemia. Leukemia. 2017;31(3):747–751.
  9. Cheng CK, Wang AZ, Wong THY, et al. FNDC3B is another novel partner fused to RARA in the t(3;17)(q26;q21) variant of acute promyelocytic leukemia. Blood. 2017;
  10. Jansen JH, Lowenberg B. Acute promyelocytic leukemia with a PLZF-RARalpha fusion protein. Semin. Hematol. 2001;38(1):37–41.
  11. Petti MC, Fazi F, Gentile M, et al. Complete remission through blast cell differentiation in PLZF/RARalpha-positive acute promyelocytic leukemia: in vitro and in vivo studies. Blood. 2002;100(3):1065–1067.