Leukemia

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. 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.

• Hx of myelodysplastic syndrome?
• Chemotherapy?
• Down syndrome?

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).

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).

• Assoc. with myeloid sarcoma.

Microscopic:

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

IHC:

• CD2+ -- common.

See also

• Lymphoma.
• Myelodysplastic syndromes