Partial lack of BCL2 in follicular lymphoma: An unusual immunohistochemical staining pattern explained by ongoing BCL2 mutation.

Follicular lymphomas are characterized by overexpression of BCL2 which, in the large majority of cases, is due to a t(14;18) translocation which juxtaposes the BCL2 locus to the immunoglobulin heavy chain locus (IGH). Here, we report partial absence of BCL2 immunohistochemical staining in a case of FL, due to a mutation in the part of BCL2 that encodes the epitope for the most frequently used antibody against BCL2. This finding shows that mutations in BCL2 occur in an ongoing process in follicular which can give rise to unusual immunohistochemical staining patterns.