Utility of Peripheral Blood Flow Cytometric Blast Enumeration Reporting in Patients without Prior Hematologic Malignancy

Background: The significance of documenting the enumerated data of low levels of blast events (CD34+/CD117+) by peripheral blood flow cytometry studies is largely unaddressed in the literature. The presence of a blast population in peripheral blood of individuals without documented appropriate explanation (such as treatment with a colony-stimulating factor) can be the very first indication of an evolving hematolymphoid neoplastic process. We aim to identify a threshold of quantified blast events on peripheral blood flow cytometric studies that may alert medical professionals of a possible disease process affecting the bone marrow.

Methods and materials: Peripheral blood flow cytometry studies performed by the clinical flow cytometry laboratory at the University of California Davis Medical Center between 2015 and 2020 that were detected to have less than or equal to 1% blast population were evaluated. Patients with a history of a known hematologic malignancy at the time of the aforementioned peripheral blood flow cytometry study were excluded. The remaining cases from patients without a known hematological malignancy were investigated.

All flow cytometry events were analyzed by multiparametric 10-color flow cytometry using an extensive panel of monoclonal antibodies. The data events were analyzed with Kaluza® software. Percentages of blasts in patients with progression to a hematologic malignancy were compared with the group of patients without progression to a hematologic malignancy. The results of this comparison were utilized to establish a threshold of the presence of CD34+/CD117+ blasts that may warrant formal reporting and recommendations of additional studies.

Results: A total of 165 flow cytometry cases from 2015-2020 were evaluated. The patients' electronic medical records were reviewed in order to determine the presence of a prior hematolymphoid malignancy and to evaluate for the progression of a malignancy after the flow study. Of the cases reviewed, 110 were excluded due to the presence of a prior hematolymphoid malignancy. The remaining 55 cases were separated into a group who on follow up had no progression to a hematolymphoid malignancy (n=50), and a second group who developed a hematolymphoid malignancy (n=5) (see figure). The mean percent of CD34+/CD117+ events in the group of patients who progressed to a hematolymphoid malignancy was higher than the non-malignancy control group (0.80% vs 0.40% of total flow cytometry events respectively). The mean percent of CD34+ events in the group of patients who had a malignancy was slightly higher than the control non-malignant group mean percent CD34+ events (0.248% vs 0.220% of total flow cytometry events respectively).

Conclusions: We identified a small percentage of patients with no known hematolymphoid malignancy and low levels of blasts on peripheral blood flow cytometry study who later developed a hematolymphoid malignancy (5/55 = 9%). On further investigation, a slightly elevated level of CD34+/CD117+ blast events in these patients was noted. Of the patients who did not develop hematolymphoid malignancies, a significant percentage had non-malignant inflammatory conditions. Based on our current assessment, some patients with low levels of circulating blasts detected by flow cytometry may necessitate follow-ups, including bone marrow evaluation. The presence of cytopenias and/or elevated inflammatory markers may further assist in the decision to proceed with additional hematologic work-up.

No relevant conflicts of interest to declare.