The diagnosis and classification of cutaneous lymphomas is a challenge for the dermatopathologist. This is particularly true for determining the distinction between a malignant lymphoma and a benign reactive infiltrate (pseudolymphoma). Recent advances in molecular genetics, as the determination of clonality of lymphoid infiltrates, have emerged as an important tool to overcome these diagnostic dilemmas. In our experience, more than 90% of cutaneous T-cell lymphomas have a rearrangement of the T-cell receptor ~{ chain gene, whereas clonal rearrangements in cutaneous 1″-cell pseudolymphomas could not be found. However, the demonstration of clonality does not necessarily indicate malignancy. There have been several reports that have identified clonal lymphoid proliferations in pityriasis lichenoides et varioliformis acuta, pseudolymphomas, and lichen planus. For this reason one must carefully evaluate the information that is provided by these techniques. The results should always correlate with clinical, histologic, and immunophenotypic data to achieve the correct diagnosis.

The diagnosis and classification of cutaneous lymphomas is a challenge for the dermatopathologist. This is particularly true for determining the distinction between a malignant lymphoma and a benign reactive infiltrate (pseudolymphoma).