Follicular lymphoma (FL) is one of the indolent non-Hodgkin lymphomas (NHLs), meaning its cells divide slowly, and it is the second most common of them in the United States. It makes up to 30% of new cases of NHL. The median age at diagnosis is about 60 years, about 80% of cases are already in an advanced stage, and bone marrow involvement is seen in 60%.
Diagnosis
FL is usually easy to recognise on the histological specimen because of the follicular pattern the cells form. As with the other lymphomas, the diagnosis is then confirmed by flow cytometry or immunohistochemistry. The most common translocation is t(14;18), which places the BCL2 gene beside the immunoglobulin heavy-chain locus, so the tumour cell cannot trigger its normal programmed death and instead accumulates. The main biomarkers are CD19+, CD20+, CD10+, BCL2+ and BCL6+.
Grading and overall survival
FL is subclassified by the type of cells seen in the specimen — small cells, large cells, or a mixture — and the WHO grading counts the large cells in each high-power field (the area seen under high magnification of the microscope):
| Grade | Large cells per high-power field |
|---|---|
| I | fewer than 5 |
| II | about 6–15 |
| III | more than 15 |
Grade III is subdivided: grade IIIa shows a predominance of centrocytes (small cells), while grade IIIb shows sheets of centroblasts (large cells). Grade IIIb is a very aggressive form and is considered as DLBCL (diffuse large B-cell lymphoma) for treatment strategy. The more large cells in the high-power field, the lower the overall survival.