Most cutaneous T-cell lymphomas demonstrate a malignant population with a CD4+ phenotype. In rare cases, CD8+ phenotypes have been described based on immunostaining of skin specimens. Although some CD8+ lymphomas have an indolent course, others, such as CD8+ epidermotropic cytotoxic T-cell lymphomas, are typically more aggressive. To our knowledge, involvement of peripheral blood or cerebrospinal fluid with a malignant population of CD8+ cells demonstrated by flow cytometry and T-cell receptor gene rearrangement has not been previously described.
We describe a patient with a CD8+ cutaneous T-cell lymphoma with an initially indolent course and early stage diagnosed on the basis of a skin biopsy specimen. However, when flow cytometry was performed looking specifically at CD8+/CD4− cells in the peripheral blood and cerebrospinal fluid, a malignant population of CD8+/CD4−/CD26−/CD7− cells was discovered.
It is important for prognosis and treatment to be able to identify CD8+ epidermotropic cytotoxic T-cell lymphoma and separate it from other relatively indolent CD8+ lymphomas. Furthermore, detection of an abnormal CD8+/CD26−/CD7− T-cell population within the peripheral blood has important prognostic and therapeutic implications. The use of flow cytometry looking for abnormal CD8+ populations in the peripheral blood or cerebrospinal fluid can assist with this critical information.