A low-grade follicular lymphoma may transform to a more aggressive form over time, often a diffuse large B-cell lymphoma (DLBCL). Rarely the lymphoma may transform to a blastic (blastoid) form that may mimic acute leukemia. The blastic transformation tends to follow an aggressive course with poor response to therapy and a high mortality rate.
Diagnostic features:
(1) history of low-grade follicular lymphoma or residual foci in histologic sections or flow cytometry
(2) diffuse growth of atypical lymphoid cells with high nuclear-to cytoplasmic ratio and fine nuclear chromatin resembling a lymphoblast
(3) presence of similar blastic cells in the peripheral blood smear and bone marrow
Immunophenotype:
(1) CD10 positive
(2) bcl-2 positive
(3) bcl-6 positive with structural abnormalities (allelic loss/gain, rearrangement)
(4) cyclin D1 negative
(5) TdT negative
(6) usually CD43 positive
(7) variable expression of CD20
t(14;18) is typically absent (usually present in follicular lymphoma)
