Peripheral T-cell lymphoma with a "follicular" pattern and the perifollicular sinus phenotype.

We report a case of peripheral T-cell lymphoma (PTCL) with an exclusively "follicular" pattern at one lymph node site and a diffuse pattern at a second lymph node site. Molecular studies confirmed the clonal identity of the tumor at both sites. In the lymph node showing a follicular pattern, the tumor cells appeared to infiltrate follicles where the perifollicular sinuses remained patent. The infiltrated follicles retained nonneoplastic B cells and a follicular dendritic cell network. By contrast, in the lymph node showing diffuse involvement, intranodal sinuses were no longer identifiable and there was no evidence of tumor cells infiltrating follicles. The tumor immunophenotype was influenced by the pattern: the follicular component was positive and the diffuse component was negative for bcl-6 and CD31. We suggest that the follicular growth pattern in this case of PTCL arose secondarily to tumor spread via the perifollicular sinus.