Follicular lymphoma mimicking progressive transformation of germinal centers.

Three cases of a morphologically distinctive "floral" variant of follicular large cell lymphoma are presented. In each instance, the diagnosis of theoretically "florid" progressive transformation of germinal centers (PTGC) was made or considered. The features that separate this pattern of lymphoma from reactive follicular hyperplasia with PTGC include involvement of all nodules without the presence of any reactive germinal centers, a homogeneous proliferation of large transformed lymphocytes with a markedly decreased or absent population of phagocytic histiocytes, and extension by abnormal cells into the perinodal adipose tissue. If the desirability of frozen section tissue immunophenotyping is anticipated, these lymphomas would be distinguished from PTGC by monotypic staining for light chains.