1. There is no cytogenetic abnormality that is diagnostic of FL
2. 60% express surface Ig M, 40% Ig G
3. Pediatric type in adults can have a grade 3 FL appearance, but is lacking in BCL2 IHC or t( 14;18) and has high cure rates. Typically stage I/II. Has mutations in MAP2K1 and loss of cmyc, BCL2, BCL6.
4. When FL involves the gut, it is usually in the duodenum and involves the mucosa alone. Duodenal-type FL should be differentiated from systemic FL involving the gastrointestinal tract. Features that point to systemic FL include transmural infiltration of the organ wall, regional lymph node involvement, and involvement of the large intestine.
5. Classical FL is the most common indolent NHL. There are 4 variants.
a. In situ follicular neoplasia: no typical FL features in the LN but high expression of Bcl2 and CD10. Such patients require full work up to rule out FL. If they do not have FL, the prognosis is unclear.
b. Duodenal variant as above
c. Pediatric-type FL should be distinguished from the more aggressive entity "large B-cell lymphoma with IRF4 rearrangement
6. Prognosis: FLIPI or PRIMA-PI
- High-risk FLIPI (three or more adverse factors) – median PFS 42 months, two-year OS 87 percent
- Intermediate-risk FLIPI (two adverse factors) – median PFS 70 months, two-year OS 94 percent
- Low-risk FLIPI (zero to one adverse factors) – median PFS 84 months, two-year OS 98 percent
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