Leukemia

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The article addresses leukemia, which is uncommonly seen by anatomical pathologists. It is a subset of hematopathology. Lymphoma is discussed in the lymphoma article, and overlaps somewhat with this article as the clear distinction between the two is historical.

Definition

All of the following:[1]

  1. Morphologic abnormalities.
  2. >20% blasts or recurrent cytogenetic abnormality.

Some recurrent cytogenetic abnormalities:

  • t(8;21).
  • inv(16).
  • t(15;17).

Histomorphologic overview

Disease/Feature Blast size Auer rods Granulation of cytoplasm
AML larger present present
ALL smaller none absent or present

Clinical factors

Clinical are important in the classification of leukemia.

Algorithms

There is a nice set of algorithms from D. Arber - that were presented at the 2009 USCAP.

Leukemia classification

AML:

  1. AML.
  2. AML with recurrent cytogenetic abnormalities.
  3. AML from MDS.
  4. AML in the setting of Down syndrome.

ALL:

  1. B cell.
  2. B cell with recurrent cytogenetic abnormalities.
  3. T cell.

AML with recurrent cytogenetic abnormalities

t(8;21)

  • t(8;21)(q22;q22).[2]

IHC:

  • CD34+, CD13+, MPO+ (cytoplasm), CD33+ (weak).
  • CD56+, CD117+.
    • Usu. assoc. with a bad prognosis.

Flow cytometry:

  • CD19+, PAX5+, CD79a +/-.

inv(16)

  • inv(16)(p13.1q22).[3]
  • Assoc. with myeloid sarcoma.

Microscopic:

  • Blast count usu. ~20% (low).
  • Eosinophilic granules.
    • Used to be classified as "M4" with eosinophilia.

IHC:

  • CD2+ -- common.

t(15;17)

  • t(15;17)(q22;q12).

Comes in two flavours.

Microscopic (Hypergranular or typical APL):

    • Bean-shaped nucleus or bilobed nucleus.
    • Buddles of Auer rods - known as "Faggot cells".

Microscopic (Microgranular or hypogranular APL):

  • Bilobed nuclei with nuclear overlap. (???)
  • Absence of granules on light microscopy.

IHC:

  • CD2+, CD34+/-, CD56+/-.

Flow cytometery:

  • CD34-, HLA-DR-.
  • CD33+, CD13+/-, CD117+ (weak), CD56+/-.

Clinical:

  • Assoc. with DIC.
  • Treatment: ATRA.

Variants:

  • t(11;17) -- ATRA doesn't work.
  • t(17;17) -- ATRA doesn't work.
  • t(5;17). (???)

t(9;11)

  • t(9;11).

Microscopic:

  • Monoblastic morphology. (???)
  • Myelomonocytic morphology. (???)

Clinical:

  • +/-DIC.
  • Usu. children.

IHC:

  • CD33+, CD65+, CD4+, HLA-DR+.
  • CD34+. (???)
  • CD13+. (???)

See also

References

  1. D. Good. 21 March 2011.
  2. Berger, R. (1994). "Translocation t(8;21)(q22;q22): cytogenetics and molecular biology.". Nouv Rev Fr Hematol 36 Suppl 1: S67-9. PMID 8177719.
  3. Lu, CM.; Murata-Collins, JL.; Wang, E.; Siddiqi, I.; Lawrence, HJ. (Dec 2006). "Concurrent acute myeloid leukemia with inv(16)(p13.1q22) and chronic lymphocytic leukemia: molecular evidence of two separate diseases.". Am J Hematol 81 (12): 963-8. doi:10.1002/ajh.20716. PMID 16917916.