CNS lymphoma was also considered due to the dense cellularity and angiocentric pattern of inflammatory infiltrate but was ultimately excluded by immunohistochemistry, which demonstrated a polyclonal population of B and T cells (Figure 3a,b), along with a marked polytypic plasma cell reaction confirmed by CD138 and mixed kappa/lambda staining (Figures 2d, 2e, and 2f). This evidence concerns the gene SDC1 and primary central nervous system lymphoma.