Immunophenotypic and molecular features of cuplike morphology in AML
BHS GAM 2020
A. Louwagie, B. Cauwelier, H. Devos, J. Emmerechts
 Department of Laboratory Medicine, AZ Sint-Jan Hospital, Brugge-Oostende, Bruges, Belgium

Background
Leukemic blast morphology supplemented by immunophenotyping may provide clues to a specific category of the WHO 2016 classification of AML. Nuclear invaginations, referred to as ‘cuplike’ nuclei have been associated with a lack of CD34 and HLADR expression and with mutations in NPM1 and FLT3. 

Objectives
To evaluate the association between cuplike blasts (CLB) and specific immunophenotypic and molecular patterns based on a literature study and the evaluation of de novo AMLs at our institution. 
 
Methods
A literature study was based on 7 publications. 
Bone marrow slides of all de novo AMLs at our institution between January 2018 and May 2019 (n=41) were reviewed for % of CLB (as % of total blasts), immunophenotype and mutational status of NPM1 and FLT3 by 1 analyst blinded for all results.

Results
Inconsistent results were found in literature as studies differed in definition of CLB and in inclusion criteria. In most studies, the definition of cuplike AML is restricted to cases with ≥10% CLB. 
At our institution, 5/41 (12%) de novo AMLs had ≥10% CLB, all demonstrating mutated FLT3. HLADR expression was absent in only 1/5 cases, whereas CD34 in 3/5 cases. These 3 cases all showed mutated NPM1. In 5 additional cases with 5-9% CLB, 3 cases demonstrated NPM1 mutation, of which 2 with concomitant FLT3 mutation. These 3 cases all lacked CD34 and HLADR expression. 
Not all cases with FLT3 (n=13/41, 32%) and/or NPM1 (n=10/41, 24%) mutation demonstrated CLB.

Conclusions
At our institution, 24% of de novo AMLs showed ≥5% CLB. All cases with ≥10% CLB showed FLT3 mutation, irrespective of absence of CD34 or HLADR expression. Inversely, only 2/5 cases with 5-9% CLB showed FLT3 mutation. Interestingly, NPM1 mutation seemed to be strongly correlated with concomitant lack of CD34 expression in both subgroups.