Follicular lymphoma is the second most common lymphoma; it accounts for 20% of all lymphomas.
Follicular lymphoma is predominately a disease of Western countries such as the USA, Europe and Australia. The incidence is much less in Asia, Africa and South America. Women are more commonly affected (1.7:1); the mean age is in the 50s.
Aetiology is unknown.
Follicular lymphoma has two usual patterns:
- Low grade lesions (Grade 1 - 2) are characterised by an indolent course
- High grade lesions (Grade 3) are characterised by relatively rapid progression
Most cases are widespread at presentation.
Most patients are asymptomatic at presentation, even with widespread disease.
Macroscopically, lesions are light tan and may be nodular. Microscopically, there are several characteristic features that are also important in staging:
- Follicular tumours consist of a variable population of centrocytes (small cells, small irregular nuclei) and centroblasts (large cells, visible nucleoli, abundant cytoplasm)
- The ratio of centrocytes to centroblasts determines grade:
- Grade 1 = 0-5 centroblasts per high power field
- Grade 2 = 6-15 centroblasts per high power field
- Grade 3A = Centrocytes present
- Grade 3B = Solid sheets of centroblasts
- The clusters of centrocytes/blasts typically form large follicles which lack the usual polarity and other cells of normal follicles.
Follicular lymphoma cells:
- Stain positively for CD19/20/22/79a (B-Cell antigens)
- Stain positively for BCL2 and BCL6
- Usually express CD10
Some high grade cases have an altered expression.
The typical genetic abnormality is a translocation of chromosomes 14 and 18, written as t(14;18).
- The BCL2 gene, located on chromosome 18, is attached to the promoter region for an immunoglobulin heavy chain gene on chromosome 14.
- This leads to overexpression of BCL2, an anti-apoptotic protein that promotes cell survival
High grade follicular lymphomas may often lack this translocation. A number of other genetic abnormalities are also seen.
Staging is via the Ann Arbor system. Prognosis is via FLIPI - Follicular Lymphoma International Prognostic Index, although the advent of rituximab has altered the approach to treatment of follicular lymphoma significantly. The five factors for FLIPI, marked as 'yes' or 'no', are:
- 5+ nodal sites
- Abnormal LDH
- Age > 60
- Ann Arbor Stage 3 or 4
- Haemoglobin < 12 mg/dL
These factors then combine to give good, intermediate or poor prognosis:
|5 year survival||10 year survival|
This table was based on the Mabthera website.