Background and study purpose: Detection of monocytic cells (MCs) and their aberrancy is important in the diagnoses of monocytic leukemias [chronic myelomonocytic leukemia (CMML), acute MML (AMML), and acute monocytic/monoblastic leukemia (AMoL)]. MCs may be identified by cytomorphology (CM), enzyme cytochemical staining with nonspecific esterases, flow cytometric analysis (FCA), and immunohistochemical analysis (IHCA); their aberrancy, by FCA or IHCA. As aberrant antigen expression on MCs is not detected by CM or enzyme cytochemical staining and as there may be instances of "dry tap" or a fresh bone marrow aspirate is not available for further analysis, the primary and specific purpose of this study is to globally compare the detection of MCs and their aberrancy by the 2 methods of FCA and IHCA.
Procedures: Forty bone marrow (aspirate, clot, and biopsy) samples (7 CMMLs; 33 AMMLs and AMoLs) are evaluated by CM, FCA (complete immunophenotypic panel), and retrospective IHCA (CD2, CD3, CD14, CD33, CD56, CD68, CD123, and CD163).
Results: Forty-five percent showed a higher percentage of MCs by FCA than by CM. In addition, CD14, CD2, and CD56 detections on MCs showed greater sensitivity by FCA than by IHCA. By IHCA, CD14 showed the highest specificity for MCs (CD163, less specificity; CD68 and CD33, low specificity). CD123 did not correlate with CD14 or CD163, stained a subset of AMMLs/AMoLs, and stained no CMMLs. By comparing IHCA in clot versus biopsy sections, CD56 showed highest correlation (93%), followed by CD14 (85%) and CD33 (70%). CD68, CD163, and CD123 showed greater reactivities in clots (48%, 44%, and 35%, respectively), likely because of decalcification.
Conclusions: FCA is most sensitive in detecting MCs and their aberrancy. By IHCA, CD14 is most specific. CD123 inconsistently marks AMMLs/AMoLs. Further evaluation of CD123 may determine the usefulness of CD123 in AML subtyping and possible prognostic implications and targeted therapy.