Monoclonality of intraepidermal T lymphocytes in early mycosis fungoides detected by molecular analysis after laser-beam-based microdissection

The identification of neoplastic lymphocytes in early lesions of mycosis fu ngoides is difficult because of the scarcity of the infiltrate and the pres ence of reactive T lymphocytes admixed with neoplastic cells. Molecular ana lysis of the T cell receptor gene rearrangement using the polymerase chain reaction technique demonstrates monoclonality only in a proportion of these cases. The exact location of the malignant clone is unknown, and at presen t it is not clear whether neoplastic cells in early lesions reside within t he epidermis, the superficial dermis, or both. We analyzed skin lesions fro m five patients with early mycosis fungoides using the polymerase chain rea ction technique after microdissection of the specimens. In each case the ep idermis was separated from the dermis using a laser-beam microdissection te chnique. Three samples were prepared from each lesion: one containing only the epidermis, one only the superficial dermis, and one the entire specimen . A distinct band could be observed in the epidermal sample in four cases, indicating the presence of an intraepidermal monoclonal population of T lym phocytes. The dermal sample revealed a monoclonal pattern in two cases (bot h of them showing clonality also within the epidermis). Analysis of the ent ire specimen revealed a monoclonal pattern only in two cases. Our results d emonstrate that intraepidermal lymphocytes in early mycosis fungoides often show a monoclonal pattern of T cell receptor gene rearrangement. Microdiss ection of biopsy specimens may enhance the sensitivity of the polymerase ch ain reaction technique.