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.