APL

Question 1

What is the difference in expression of CD15 in normal vs. leukemic promyelocytes?

Answer 1

• leukemic promyelocytes typically express low to absent CD15

Question 2

What is the immunophenotype of APL?

Answer 2

• CD13 heterogeneous
• CD33 strong and uniform
• CD117 heterogeneous
• MPO positive
• Negative for: CD34 and HLA-DR
• CD15 low to absent
• CD11a and CD18 low to absent
• CD133 (myeloid progenitor antigen) negative

Question 3

What are the differences of the immunophenotype in the microgranular variant of APL?

Answer 3

• may have lower SSC similar to normal blasts
• variable expression of CD34
• CD2 is often positive

Question 4

The expression of CD2 in the microgranular variant of APL has been associated with what?

Answer 4

• leukocytosis
• increased occurrence of thrombotic events
• shorter complete remission duration (described in some studies)

Question 5

Are there any differences in the immunophenotype of therapy-related APL or APL with variant translocations?

Answer 5

• No

Question 6

What is CD56 expression by APL associated with?

Answer 6

• seen in only a subset of APLs (~15%)
• associated with a poor prognosis

Question 7

What other types of blast morphology (non APL) have been described in association with a negative CD34 and HLA-DR?

Answer 7

• non-APL AML morphology: cup-like nuclear indentations
• often have normal cytogenetics and contain mutations of NPM1 and FLT3

Question 8

What are some immunophenotypic similarities of APL to monocytic leukemias ?

Answer 8

• high levels of CD33 expression and positivity for CD64

Question 9

How can APL be immunophenotypically differentiated from a monocytic leukemia?

Answer 9

• APL shows bright expression of MPO and negative HLA-DR
• Monocytic leukemias should be the opposite

Question 10

After therapy, immunophenotypes of APL may change. What are some changes that may be seen occasionally?

Answer 10

• upregulation of CD11b, CD11c and CD158
• immunophenotype shows differences from normal promyelocytes
• CD15 may be decreased as compared to normal

Question 11

What can be seen in APL at relapse?

Answer 11

• similar morphology
• relatively increased expression of CD34 and HLA-DR with decreased CD13