Episode 002: Heme Path Series Pt. 1 - Flow Cytometry
Major Points Covered:
In Part 1 of our Heme Path series, we break down the logistics and applications of flow cytometry.
Take Aways:
Cancer = cells that clone themselves uncontrollably due to mutations.
Purpose of flow cytometry is to assess phenotype of the cell by characterizing cell surface markers (CD markers for example). For blood cells, this is called the “immunophenotype”.
Testing requires live cells in suspension and can’t be fixed. Remember to keep all lymph node biopsies in suspension when sending for flow cytometry.
Flow tells us that if cells share the same abnormal expression of cell surface markers, they are clonal and therefore raise concern for cancer.
Flow tells us if cells have specific cell surface markers that we can target for treatment. For example, expression of CD20 can be targeted by the drug Rituximab.
If a clone is identified at diagnosis, flow cytometry can be used to sift through thousands of cells to see if a single clone with the original abnormal phenotype is left over. This is called minimal residual disease (MRD) testing and is a great way to monitor response to treatment and identify if any tiny amount of cancer is left over.
There are a variety of indications to send flow cytometry but the bottom line to remember is that we are trying to find an abnormal clonal population of cells. You may not see anything abnormal in the peripheral blood because those cells are living in the bone marrow.
Blasts reported on the CBC w/ diff is done based on visual inspection of morphology by a hematology lab scientist or pathologist; but can only confirm if it is truly a blast with flow cytometry.
Always send bone marrow biopsy aspirate samples for flow cytometry.
We use flow cytometry as one piece of the larger puzzle to prove clonality and make a diagnosis. Other uses are for determination of targeted treatments based on cell surface markers and to identify any amount of residual disease (MRD testing by flow cytometry).
References
https://ashpublications.org/blood/article/111/8/3941/24550/Flow-cytometric-immunophenotyping-for-hematologic - ASH review article on use of flow cytometry to diagnose heme malignancies.
https://onlinelibrary.wiley.com/doi/10.1002/cyto.b.20365 - Bethesda International Consensus Guidlines for Flow Cytometry in 2006
https://www.bloodresearch.or.kr/journal/view.html?uid=2357&vmd=Full& - Minimal residual disease testing in ALL as an example of another clinical use of flow cytometry
http://www.cyto.purdue.edu/archive/flowcyt/research/pdfs/encyclopedia_2004.pdf - Good article explaining the complexities of the flow cytometry technique
