Pediatric primary bone lymphoma-diffuse large B-cell lymphoma: morphologic and immunohistochemical characteristics of 10 cases.

Most primary bone lymphomas (PBLs) are diffuse large B-cell lymphomas (DLBCLs). Pediatric PBL-DLBCL has a favorable prognosis but remains poorly characterized. Herein, 10 such cases are detailed. They involved 11- to 20-year-old males with bone lesions that were often painful. They were diagnosed often after months to years of symptoms, suggesting an indolent disease. All were successfully treated with chemotherapy with or without radiotherapy (0.5- to 24-year followup). Biopsy revealed that the lymphomas were paratrabecular or diffuse and were medium- to large-sized with round to irregular nuclei, dispersed chromatin, indistinct to small nucleoli, and abundant cytoplasm. Other features included varying levels of necrosis, cytoplasmic retraction, and myeloid hyperplasia. All cases marked as mature B cells, and most were CD10+ (7/10). Typical centroblastic morphologic features with nucleoli were rare, multilobated nuclei were uncommon, and CD10 negativity did not predict poor prognosis, unlike in the adult PBL-DLBCL. These findings suggest that pediatric and adult PBL-DLBCLs are distinct entities.