Submitting Author: Collie, Angela Maria Bookwalter, MD, PhD
Institution: Cleveland Clinic
Additional authors:Fareed H. Barakat, M.D, Eric D. Hsi, M.D.
Session: Acute leukemias of ambiguous lineage

A 15 year old girl with no significant past medical history presented with cervical lymphadenopathy and dizziness. Complete blood count revealed elevated white blood cells with 35% circulating blasts. A cervical lymph node biopsy was performed and showed diffuse effacement of the node. Two weeks later bilateral bone marrow biopsy was performed.

The cervical lymph node biopsy showed effacement of the node by mononuclear cells consistent with blasts. These cells were of intermediate size with round to irregular nuclear contours, fine chromatin, and single to multiple nucleoli. Scattered mitotic figures were identified. The bone marrow biopsy showed a left shift with a similar diffuse infiltrate of intermediate-sized blasts with fine chromatin. 30% blasts were noted in the bone marrow aspirate, but this was not received for review.

Flow cytometry was performed at the referring institution and showed an abnormal population representing 37% of bone marrow cells. This population was positive for CD3 (dim), CD5 (dim), CD7, CD33, CD34, CD79a, and terminal deoxynucleotidyl transferase (TdT). A subset was positive for CD11b and myeloperoxidase.

Immunohistochemical stains performed on the lymph node and bone marrow biopsies demonstrated that the blasts were positive for CD3 (weak), CD34, TdT, and myeloperoxidase (weak); they were negative for CD20 and muramidase. The blasts were also negative for NOTCH1, suggesting the absence of activating alterations in this pathway

Fluorescence in situ hybridization (FISH) with dual color, dual fusion probes on the peripheral blood was negative for a BCR/ABL1 translocation. FISH on the lymph node biopsy using a dual color, break apart probe was positive for an MLL (11q23) translocation.

Cases of B/myeloid mixed phenotype acute leukemias with MLL translocation have been described fairly often in large series examining molecular characteristics of mixed phenotype acute leukemias. However, T/myeloid mixed phenotype acute leukemias represent a smaller percentage of biphenotypic leukemias, and only two cases with MLL translocation, by current World Health Organization criteria, have been reported. This case is an example of a rare MLL translocation in a case of T/myeloid mixed phenotype acute leukemia.

Mixed phenotype acute leukemia, T/myeloid, with t(v;11q23); MLL rearranged

Additional immunostains performed by the conference consensus group:

MPO: Positive in blasts
CD: Positive in blasts

Mixed phenotype acute leukemia, T/myeloid, with t(v;11q23); MLL rearranged

Case 256