This randomized, placebo-controlled phase 3 study is planned to enroll approximately 235 treatment-naïve subjects with high-risk Diffuse Large B-Cell Lymphoma (DLBCL). Subjects will be randomized 1:1 to R-CHOP plus enzastaurin or R CHOP (plus placebo during induction). All subjects will receive up to 6 cycles (3 weeks per cycle) of treatment. PET/ CT will be used to assess radiographic response at the end of treatment. Each subject's treatment assignment will be unblinded after initial phase of treatment. Subjects randomized to the enzastaurin arm who have a response will be offered maintenance treatment of the study drug for up to 2 additional years.