Immunophenotyping
Immunophenotyping refers to tests used to identify unique cell types based on the types of antigens or markers on the cell’s surface.1 Such tests are employed at the initial diagnostic workup and are essential to confirm a diagnosis of FL.2
Immunophenotype, in addition to histology and cytogenetic studies, helps establish the diagnosis of FL.2 The immunophenotype characteristic of FL is shown in the table below.
Subtype | Typical immunophenotype2 |
Follicular lymphoma (FL) | CD10+, BCL2+, CD23+/-, CD43-, CD5-, CD20+, BCL6+ |
Two common immunophenotyping tests are immunohistochemistry (IHC) and flow cytometry (FC).2
Immunohistochemistry (IHC)3
- A lab test that uses labeled antibodies to test for certain antigens (markers) in a tumor sample
- Antibodies are usually linked to an enzyme or a fluorescent dye
- When the antibodies bind to the antigen in the tissue sample, the enzyme or dye is activated, and the antigen can be seen under a microscope
Flow Cytometry (FC)3
- A method of characterizing the antigens in a tumor sample by staining them with a light-sensitive dye, placing them in a fluid, and passing them in a stream before a laser or other type of light
- The measurements are based on how the light-sensitive dye reacts to the light
- FC also measures the number of cells in a sample, the percentage of live cells in a sample, and certain characteristics of cells, such as size, shape, and the presence of tumor markers on the cell surface
Additional IHC Markers in FL
In addition to assessing chromosomal rearrangements and the markers required to establish a diagnosis of FL, IHC can be used to measure the expression of different molecular markers, and may be an important part of the workup for a patient with FL.2
Some examples of IHC markers that are tested in a patient with suspected FL include2:
- IRF4/MUM1 (for FL grade 3)
- Cyclin D1 (to exclude MCL)
- Ki-67 (Ki-67 expression is associated with a high proliferation index. A Ki-67 fraction of >30% may be associated with more aggressive clinical behavior; however, there is no evidence that Ki-67 expression should be used to guide treatment)
Cytogenetics
Cytogenetic tests, which combine principles of cytology (the study of cells using a microscope) and genetics, may be useful in certain circumstances for the diagnosis of FL. Genetic abnormalities may be detected by karyotyping (examination of chromosomes in a sample of cells) or fluorescent in-situ hybridization (FISH).2,3
- Karyotyping: a method by which chromosomes are visualized, allowing detection of large rearrangements or abnormalities4,5
- FISH: a method that detects the presence of specific proteins in a biologic sample using fluorescently-tagged antibodies that bind to antigens of interest6
During the initial diagnostic workup of a patient, FISH and/or karyotyping may help establish the diagnosis of FL.1 In FL, the translocation between chromosomes 14 and 18—t(14;18)—occurs in ~90% of all cases.7

Reproduced with permission from Atlas of Haematological Cytology

Reproduced with permission from Atlas of Genetics and Cytogenetics in Oncology and Haematology. http://AtlasGeneticsOncology.org
Molecular Profiling
Molecular analysis may be useful during diagnosis of FL.2 If these tests are ordered, DNA is isolated from a patient and its entire sequence is determined or a panel of known cancer-related genes are sequenced.8,9 Such profiling will detect changes in specific genes in the tumor cells, which may inform diagnosis, prognosis, and treatment.8,10
- While mutations have been observed in FL that may be related disease biology, these are still being elucidated. There are currently no known mutations that can be used to define FL11