Flow cytometry to detect bone marrow involvement by follicular lymphoma

Area of Science:

• Hematology
• Oncology
• Immunology

Background:

• High-quality data on bone marrow involvement (BMI) in follicular lymphoma (FL) assessed by flow cytometry (FC) is limited.
• Accurate assessment of BMI is crucial for staging and treatment decisions in FL.

Purpose of the Study:

• To establish and validate a prospective flow cytometry protocol for evaluating BMI in FL.
• To compare the diagnostic performance of FC with established methods like histopathology, IGH gene rearrangement, and PET imaging.

Main Methods:

• A prospective protocol using a 10-color flow cytometry tube and acquisition of 500,000 leukocytes was implemented.
• Bone marrow involvement by FC was compared against a gold standard of histopathology combined with IGH gene rearrangement.
• Flow cytometry results were also compared with findings from PET imaging.

Main Results:

• Flow cytometry detected bone marrow involvement in 67% of 52 FL patients, with a median leukocyte involvement of 1.2%.
• FC demonstrated high concordance with the gold standard, with only minor discrepancies (2 false negatives, 2 false positives).
• The immunophenotype of FL in bone marrow was highly heterogeneous, with variations in CD19, CD10, CD20, CD79b, CD43, and CD45 expression.

Conclusions:

• Flow cytometry is a sensitive and reliable method for detecting bone marrow involvement in follicular lymphoma.
• The established FC protocol can identify FL in the bone marrow for the majority of patients with confirmed involvement.
• The heterogeneous immunophenotypic profile of FL in bone marrow highlights the complexity of the disease at this site.