Prevalence of follicular lymphoma in situ in consecutively analysed reactive lymph nodes

Follicular lymphoma (FL) in situ is defined as strongly bcl-2-positive B cells in germinal centres of morphologically inconspicuous lymph nodes. The prevalence and biological and clinical significance of this lesion are still not clear. Therefore we aimed at the detection of the prevalence of this phenomenon in an unselected series of lymph nodes, as a surrogate for the normal population.

All 1294 reactive lymph nodes from unselected consecutive surgical specimens of 132 patients in a 3-month period were stained for bcl-2 protein. The t(14;18) translocation was investigated by fluorescence in-situ hybridization (FISH) analysis. FL in situ was identified in 22 lymph nodes in 3/132 patients (2.3%) without evidence or history of malignant lymphoma, and confirmed by detection of the t(14;18) translocation by FISH. Interestingly, in one patient, a lymph node excised 2 years before also contained FL in situ.

We found a prevalence of 2.3% for FL in situ lesions in an unselected series of lymph nodes, as a surrogate for the normal population. Taking into account the incidence of manifest FL, the risk of progression of this lesion is probably limited. It can be speculated that some FL in situ lesions do indeed represent an early step in lymphomagenesis, whereas others persist without further progression to overt FL. The underlying mechanisms, however, remain to be elucidated.