BCL-6 Overexpression Predicts Poor Response to Reduced Immune Suppression Therapy in Children with Post-Transplantation Lymphoproliferative Disease (PTLD).

Background: PTLD is a well known complication of organ transplantation. While the understanding of this disease is increasing, the diagnosis and treatment remain challenging. The clinical, morphological, and molecular findings in PTLD vary widely. Reduction of immune suppression is the treatment of choice, but is effective in only 20–50% of patients. Mutations in the BCL6 gene have been demonstrated in some lymphomas and PTLD and may have prognostic implications. A single study, in which most subjects were adults, has suggested that BCL6 mutation in PTLD predicts a lack of response to reduced immunosuppression (IS).

Objectives: To determine if BCL-6 overexpression predicts poor response to reduced IS or decreased survival in children with PTLD.

Methods: Clinical data of patients identified with PTLD at The Children’s Hospital (TCH) from 1992–2002 were obtained, including age, type of organ transplanted, subtype of PTLD, treatment received, response to treatment, relapse free survival (RFS), and overall survival (OS). Archived specimens of lesions obtained at the time of diagnosis of PTLD were evaluated for the presence of BCL-6 expression by immunohistochemistry.

Results: Between 1992 and 2002, 486 organ transplants (211 heart, 107 hematopoietic stem cell (HSC), 86 liver, 82 kidney) were performed at TCH. During that same period, 20 children were diagnosed with 21 cases of PTLD. Eleven patients had liver transplants (12.7% of transplants), 5 had heart transplants (2.4%), 3 had HSC transplants (2.8%), and 1 had a kidney transplant (1.2%). Histologic classifications of PTLD included 1 follicular hyperplasia, 9 polymorphic PTLD, and 11 lymphomas. Only 5 of 20 patients responded to reduced IS. Overall mortality was 45% (9/20). BCL-6 was overexpressed in 7 of 18 evaluable specimens from 20 patients. None of the patients with BCL-6 overexpression responded to reduced IS (p=0.05). BCL-6 overexpression was associated with monomorphic histology (p=0.02), but did not predict RFS or OS.

Conclusions: BCL-6 expression is associated with monomorphic histology and non-response to reduced IS in children with PTLD. Larger, prospective studies of BCL-6 mutation and expression are needed to verify the clinical significance of these findings.