Law, Mark E

PCNSL molecular pathogenesis in immunocompetent patients is largely unknown. Small studies suggest a role for immunoglobulin heavy chain (IGH) gene translocations. We studied the incidence of IGH, BCL6, and MYC gene rearrangements in 44 PCNSL affecting immunocompetent patients, diagnosed and treated at Mayo Clinic (1992–2006). All cases were DLBL according to the WHO classification, confined to the CNS. Interphase fluorescence in‐situ hybridization (FISH) was performed using a two‐color IGH‐BCL6 dual‐fusion probe and a two‐color MYC breakapart (BAP) probe on paraffin‐embedded tumor samples. Two‐color BCL6 or IGH BAP FISH probes were also used in cases showing extra FISH signals other than IGH‐BCL6 fusion. Sufficient tumor cells for FISH analysis using the IGH‐BCL6 and MYC probes were available in 43 and 39 cases, respectively. IGH‐BCL6 fusion was present in 6 (14%) cases, one also with a separated MYC signal. Three (7%) cases showed 3 intact BCL6 signals using both the IGH‐BCL6 and BCL6 BAP probes, indicating trisomy 3. One (2%) showed 3 intact IGH signals using both the IGH‐BCL6 and IGH BAP probes, indicating trisomy 14. Remaining 33 (77%) cases lacked abnormalities involving IGH, BCL6 or MYC. IGH‐BCL6 fusion was present in 14% of cases, 1 of which also had a translocation involving MYC and an unknown partner gene. All other cases lacked translocations involving IGH, BCL6, and MYC. The frequency of IGH‐BCL6 translocations in PCNSL is less than that seen in systemic DLBCL. Other translocations involving IGH that are not uncommon in systemic DLBCL, such as IGH‐BCL2 and IGH‐MYC, are rare to absent in PCNSL, suggesting a distinct pathogenesis for PCNSL compared to systemic DLBCL.