Background
Blasts from B acute lymphoblastic leukemia (B-ALL) may express CD56 in about 10% of cases. The presence of this marker at diagnosis is associated with an increased risk of meningeal relapse. A case is described of B-ALL which was CD56 negative at diagnosis, and expressed this marker when isolated meningeal relapse was diagnosed.
Material and Method
A 53-year-old female patient presented with neurological symptoms during maintenance therapy for B-ALL. Peripheral blood, bone marrow, and cerebrospinal fluid (CSF) were subjected to both morphological and flow cytometric analyses. The latter was carried out by a wide routine panel of MoAbs which was the same as the one at diagnosis and included CD56. Isolated meningeal relapse was diagnosed since blast cell infiltration was detected in the CSF, but not in the peripheral blood and bone marrow samples. Blast cells showed an immunological phenotype similar to that at diagnosis (cyCD79a+, CD79b+, CD19+, CD22+, CD34+, CD10+, CD20+), but characterized by the acquisition of CD56 on the surfaces of more than 90% of cells.
Results

Conclusions
This case shows that CD56 can be expressed at relapse of B-ALL and that its presence likely enables leukemic cell binding to the central nervous system (CNS). This phenomenon may be responsible for the isolated CNS relapse diagnosed in this patient.

Keywords: Precursor Cell Lymphoblastic Leukemia-Lymphoma - metabolism, Recurrence, Meninges - pathology, B-Lymphocytes - pathology, Antigens, CD56 - metabolism