Submitting Author: Paessler, Michele E, DO
Institution: The Children's Hospital of Philadelphia
Additional authors:Rebecca L. King, Gerald Wertheim
Session: AML with myelodysplasia-related changes

This patient is a 13 year-old female that presents with a CBC that was significant for WBC 59,000/uL, Hg 7.1 g/dL, Hct 21.2%, and Plt of 418,000/uL. The peripheral blood smear was reviewed and showed left-shifted myeloid series, atypical neutrophils, occasional basophils and increased blasts (~20%) with rare Auer rods. A myeloproliferative neoplasm (CML) with blast crisis was favored based on the peripheral blood. A bone marrow biopsy was obtained (see details below). Molecular studies were negative for BCR/ABL and JAK2 V617F; however the morphology of the marrow suggested that the acute leukemia may have arisen from a myeloproliferative neoplasm.

Bone marrow, aspirate: No spicules are present. Blasts comprise ~20% of the cellularity. The blasts are intermediate to large in size with oval to irregular nuclei, fine chromatin and scant to moderate amounts of cytoplasm. Rare Auer rods are present. Myeloid precursors are increased in number and show a left shift in maturation. Neutrophils with atypical nuclear lobation are seen. Megakaryocytes show hypolobated forms.

Bone marrow, biopsy: Hypercellular marrow (100%) with markedly increased myeloid cells with a left shift in maturation. Megakaryocytes are increased in number and show small hypolobated forms with clustering. Areas of fibrosis are noted, especially associated with the megakaryocytes. A reticulin stain shows increased reticulin fibrosis (MF grade 1-2).

Flow cytometry demonstrated an expanded population of blasts, 28% of total events that are positive for CD34, CD13, CD33, CD15, HLA-DR and MPO.

Paraffin immunohistochemistry performed on the bone marrow biopsy shows scattered and focally clustered CD34+ blasts. The CD34 also highlights dysplastic megakaryocytes.

The bone marrow is essentially replaced by a leukemic clone of cells. The karyotype demonstrated a deletion in the long arm of chromosome 5, which was confirmed by FISH. There was no evidence of BCR-ABL fusion by karyotype or interphase FISH.

RT-PCR for BCR/ABL fusion and JAK2 V617F mutation testing were negative.

High resolution SNP array studies confirmed the 5q deletion and also revealed a deletion in the short arm of chromosome 11. The distal breakpoint of the chromosome 5 deletion was in the NSD1 gene, and the centromeric breakpoint of the 11p15.5p15.4 deletion was in the NUP98 gene. These two apparent deletions likely reflect a cryptic rearrangement between 5q and 11p that results in a NUP98-NSD1 fusion. This finding is an independent predictor of poor prognosis with less than 10% 4 year event free survival.

This interesting case was originally thought to be an acute myeloid leukemia that transformed from a chronic myeloproliferative neoplasm, based on the peripheral blood (high WBC count and left shift in myeloid elements) and bone marrow biopsy findings. Molecular studies for BCR-ABL fusion and JAK2 V617F were negative. The karyotype demonstrated a deletion in 5q, which was confirmed on FISH and high resolution SNP array studies. Interestingly, the SNP array studies also revealed a deletion in 11p. These two deletions reflect a cryptic rearrangement between 5q and 11p that results in a NUP98-NSD1 fusion.

Translocations involving NUP98 on chromosome 11p15 occur at low frequency in acute myeloid leukemia but can be easily missed on routine karyotyping. A recent study by Hollink et al. screened cytogenetically normal pediatric and adult AML cases using NUP98/NSD1 specific RT-PCR and demonstrated 16.1% pediatric AML and 2.3% of adult AML cases harbored the NUP98/NSD1 fusion (1). This is similar to other mutations such as NPM1, CEBPA, and MLL that occur more frequently in children. The NUP98-NSD1 cases had significantly higher white blood cell counts, more frequent FAB-M4/M5 morphology and more cytogenetically normal AML, and FLT3/ITD than NUP98/NSD1 negative cases. Most importantly, NUP98/NSD1 was an independent predictor for poor prognosis with an event free survival <10% for both pediatric and adult patients (1). Even with intensive therapy NUP98/NSD1 patients were either refractory to treatment or showed early relapse (1).

NUP98/NSD1 identifies a recurrent translocation characterizing a novel, clinically relevant group of AML patients that were previously unrecognized. Interestingly, this fusion results from a cryptic translocation that is not evident on conventional karyotyping and therefore, other molecular techniques, such as SNP array, must be used.

This pediatric patient has the classic presentation and course of this newly described subtype of AML. The patient presented with a high WBC count and while she showed a deletion of 5q on the karyotype, the cryptic NUP98/NPM1 fusion was not evident on this study and could have easily been missed had SNP analysis not been performed. The patient has been refractory to all therapy in the four months since diagnosis and currently shows the leukemic clone comprising 94% of the marrow.

Reference:

1) Hollink IH, van den Heuvel-Eibrink MM, Arentsen-Peters ST, et al. NUP98/NSD1 characterized a novel poor prognostic group in acute myeloid leukemia with a distinct HOX gene expression pattern. Blood. 2011;118:3645-56.

Acute myeloid leukemia with NUP98/NSD1, a previously unrecognized subtype of AML

Acute myeloid leukemia with myelodysplasia-related changes (deletion 5q and morphology), with cryptic NUP98/NSD1 rearrangement

Case 288