Genomic imbalances during transformation from follicular lymphoma to diffuse large B-cell lymphoma

Follicular lymphoma is commonly transformed to a more aggressive diffuse large B-cell lymphoma (DLBCL). In order to molecularely characterize this histiological and clinical transformation, comparative genomic hybridization was applied on 23 follicular lymphoma and 35 transformed DLBCL tumors from a total of 30 patients. The results were also compared with our published findings in de novo DLBCL. Copy number changes were detected in 70% of follicular lymphoma and in 97% of transformed DLBCL. In follicular lymphoma, the most common alterations were +18q21 (33%), +Xq25-26 (28%), +1q31-32 (23%), and -17p (23%), whereas transformed DLBCL most frequently exhibited +Xq25-26 (36%), +12q15 (29%), +7pter-q22 (25%), +8q21 (21%), and -6q16 - 21(25%). Transformed DLBCL showed significantly more alterations as compared to follicular lymphoma (P = 0.0001), and the alterations -6q16-21 and +7pter-q22 were only found in transformed DLBCL but not in follicular lymphoma (P = 0.02). Alterations involving +13q22 were significantly less frequent, whereas -4q13-21 was more common in transformed as compared to de novo DLBCL (P = 0.01 and P = 0.02, respectively). Clinical progression from follicular lymphoma to transformed DLBCL is on the genetic level associated with acquirement of increasing number of genomic copy number changes, with non- random involvement of specific target regions. The findings support diverse genetic background between transformed and de novo DLBCL.