Mycosis Fungoides (MF) is an indolent, Non-Hodgkin's lymphoma of T cell origin (memory T helper cells) that primarily develops in the skin but can extend to other organs as well. It is the most common type of cutaneous T cell lymphoma (50% of all primary cutaneous lymphomas). It is most common in adults over 55 years of age, however it can be seen in younger patients and in the pediatric population. The male to female ratio is 2:1. Approximately one third of patients develop advanced disease involving the lymph nodes and organs. As the disease progresses, patients become progressively immunocompromised.

On microscopy, there is an epidermotropic infiltrate of an atypical clonal T cell population. The atypical T lymphocytes colonize the basal layer of the epidermis giving the "string-of-pearls" appearance. In less than 25% of cases there are also aggregates of atypical lymphocytes often in association with Langerhans cells in the epidermis, forming Pautrier's microabscesses.

The atypical lymphocytes have enlarged, hyperchromatic, cerebriform nuclei that are surrounded by a clear cytoplasm.

Immunohistochemical studies for MF include: CD3, CD20, CD4, CD8, CD2, CD5, CD7, CD30, CD56, and Ki-67. Since MF is a T cell lymphoma, the atypical lymphocytes are CD3+ and CD20-. The majority of MF cases have CD4+ neoplastic T-cells, however approximately 20% of cases can be CD8+. Loss of one pan T cell marker such as CD7 and CD5 is common. MF is CD30- and CD56- (cutaneous anaplastic large-cell lymphoma is CD30+) although there have been cases of transformed MF which were CD30+.

Other stains included in this case, see Related Content:
CD3 - LMP67496
CD20 - LMP52751
CD8 - LMP54716
CD4 - LMP70134