INTRODUCTION
Lymphocytes are the most radiosensitive peripheral blood cells due to
their inefficient DNA repair mechanisms. Lymphopenia secondary to
radiation therapy (RT) is associated with poorer progression-free
survival (PFS) and overall survival (OS) in patients with tumors of
breast, brain, gastrointestinal tract, head and neck, lung, and
pancreas.2-6 The poorer outcome in patients with
RT-induced lymphopenia is hypothesized to be secondary to a decrease in
tumor-infiltrating lymphocytes (TIL). It is known that medulloblastoma
tumors have low numbers of TIL even prior to the initiation of
RT.7-10 In patients with childhood medulloblastoma, a
recent publication demonstrated a correlation between peripheral
lymphopenia occurring during weeks 1 and 2 of craniospinal irradiation
(CSI) and risk of disease recurrence.1 However, many
patients in this study received myelosuppressive chemotherapy prior to
and/or concomitantly with RT; consequently, lymphopenia cannot be
entirely attributed to RT alone.
The purpose of this study is to examine the effect of lymphopenia during
RT in an independent population of patients with newly-diagnosed
pediatric medulloblastoma, none of whom received myelosuppressive
chemotherapy concurrently with RT.