An unusual metastatic breast cancer, characterized at first by a diffuse involvement of the lymph node areas, is described. The relapse of the disease, 3 months after ceasing treatment (CMF schedule for 16 cycles) and with the patient in apparent complete remission, massively involved the bone marrow, sparing the commonest parenchymal sites. The lymphohematogenous diffusion simulated the course of a systemic lymphoma-like disease. The behavior of this case suggests that breast cancer is a polymorphic disease: early diagnosis and treatment can modify the natural course, so no attention is paid to the variety and evolution of the presenting symptoms.