In difficult cases, in which the differential diagnosis rests between a reactive process and PCFCL, polymerase chain reaction can be used to examine the immunoglobulin heavy-chain and [KAPPA] light-chain genes.
In some instances, flow cytometry can be helpful in evaluating PCFCL. Flow cytometry is more likely to detect both CD10 and BCL2 expression and can assess light chain restriction in B cells.
Please see the Table for a summary of the considerations in the differential diagnosis of PCFCL.
Systemic/nodal follicular lymphomas can involve the skin and are histopathologically indistinguishable from PCFCL. Clinical features, in particular, lymphadenopathy, B symptoms, or other evidence of systemic or nodal disease, are critical for recognizing cases of FL involving the skin.
Patients are usually older women with rapidly growing nodules/tumors on the lower legs (Figure 4, A), (3,4,10,27) and PCDLBCL-LT has a worse prognosis compared with PCFCL, with a 5-year survival of 50%, (3,4,10,16) although improvements in survival have been seen with the inclusion of rituximab in polychemotherapy.
In some instances of PCFCL, centrocytes can be quite large and may be more than twice the size of a normal lymphocyte.
(10) While this feature is helpful in distinguishing PCFCL from PCDLBCL-LT, it can be misleading, as a mixture of B and T cells can also denote a reactive process.
The distinction between PCFCL and PCDLBCL-LT has important treatment implications in addition to prognostic implications.
(4,10) Importantly, the number of centroblasts does not affect prognosis, and, unlike nodal follicular lymphomas, PCFCLs are not graded.
In addition to pan B-cell markers (CD19, CD20, CD22, CD79a, PAX-5), PCFCLs express BCL6 and less commonly, CD10.