Treatment strategies and outcomes were assessed in 25 patients with primary breast diffuse large B-cell lymphoma (PB-DLBCL) treated between 1995 and 2016. We specifically investigated the timing of recurrence, and the roles of radiotherapy (RT) and central nervous system prophylaxis (CNS PPX). Fifty-two percent of patients received RT, and 28% received CNS PPX. Fourteen patients (56%) experienced recurrence, with 76% of relapses occurring ≥24 months after diagnosis, in contrast to reports supporting the use of 24-month event-free survival as a surrogate endpoint in the general DLBCL population. Use of RT was associated with a trend toward improved progression-free survival (PFS). Twenty percent of patients experienced CNS relapse, with no clear benefit to CNS PPX. These data emphasize the importance of long-term follow-up for PB-DLBCL patients, suggest a PFS benefit with the addition of RT, and highlight high rates of CNS relapse.