How is acute leukemias of ambiguous lineage (ALAL) classified?

Updated: Jun 18, 2020
  • Author: Enrique Ballesteros, MD; Chief Editor: Aliyah R Sohani, MD  more...
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Answer

Answer

The 2016 revision of the World Health Organization (WHO) Classification includes further refinements to the diagnostic criteria for ALAL, including molecular characterization of MPALs. [2] In the 2016 revision of the WHO Classification, the category of acute leukemias of ambiguous lineage includes the following [1] :

  • AULs
  • MPAL with t(9;22)(q34.1;q11.2); BCR-ABL1 rearranged
  • MPAL with t(v;11q23.3); KMT2A ( MLL) rearranged
  • MPAL, B/myeloid, not otherwise specified (NOS)
  • MPAL, T/myeloid, NOS
  • ALAL, NOS

Various scoring systems have been used previously; however, the 2016 WHO criteria for lineage assessment in MPAL are presented in Table 1. [1, 4, 5] It is important to recognize that these recommendations only apply to MPAL; these criteria do not apply to straightforward cases of AML or ALL in which MPAL is not a diagnostic consideration. The 2016 WHO update also emphasizes that for bilineal MPAL, it is more important that each individual blast population would meet the criteria for B, T, or myeloid leukemia, than that the specific markers below be present. [1]

Table 1. MPAL Lineage Assessment Criteria [1] (Open Table in a new window)

B-Lymphoid

T-Lymphoid

Myeloid

Strong CD19 with at least 1 of the following

strongly expressed:

  • CD79a
  • Cytoplasmic CD22
  • CD10*

Strong cytoplasmic CD3

MPO (flow cytometry, immunohistochemistry, or cytochemistry)

or

 

Weak CD19 with at least 2 of the following

strongly expressed:

  • CD79a
  • Cytoplasmic CD22
  • CD10*

or

 

Surface CD3

or

 

Monocytic differentiation

(at least 2:

  • NSE [cytochemistry]
  • CD11c
  • CD14
  • CD64
  • lysozyme)

* If CD10 is absent or cannot be assessed, assessment for PAX5 can be performed, usually by immunohistochemistry.

 

MPAL = mixed phenotype acute leukemia; MPO = myeloperoxidase; NSE = nonspecific esterase.

Of note, ALALs exclude distinct cases of AML that may express lymphoid-associated markers or ALL that may express myeloid-associated markers. For example, low-intensity myeloperoxidase (MPO) expression has been noted in otherwise typical cases of B-cell ALL (B-ALL), and the 2016 WHO guidelines caution against making a diagnosis of B/myeloid MPAL in the absence of other evidence of myeloid differentiation. [1] It is also important that flow cytometry antibodies against the CD3 epsilon chain be used, as immunohistochemical antibodies may detect the zeta chain of CD3, which lack specificity. [4] Cases of acute leukemia that may be classified in another category based on genetic or clinical features are also excluded (eg, AML with translocation t(8;21) and expression of multiple B-cell markers). Similarly, cases of AML with myelodysplasia-related changes and therapy-related AML should be classified accordingly with a comment that leukemic blasts harbor a mixed phenotype, if one is present.

See also the following:


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