Precursor B-lymphoblastic transformation of grade I follicle center lymphoma

Part of the natural history of follicle center lymphoma (FCL) is transforma tion to a more aggressive neoplasm, almost always a diffuse large B-cell ly mphoma. We describe a rare example of a precursor B-lymphoblastic transform ation of grade I FCL occurring in a 45-year-old woman 12 years after initia l presentation and 3 years after successful treatment for a diffuse large c ell transformation. The lymphoblastic lymphoma shared the same immunoglobul in heavy chain gene rearrangement as the FCL as assessed by polymerase chai n reaction amplification and direct sequencing, as well as identical kappa light chain gene rearrangements by Southern blot analysis. The immunoglobul in heavy chain variable gene sequences of both tumors showed numerous ident ical base substitutions compared with germline sequences and 3 additional m utations in the lymphoblastic lymphoma not present in the low-grade FCL. Th ese results indicate origin of the lymphoblastic process from the mature fo llicle center B-cell clone, rather than divergent origin of the 2 tumors fr om a common immature B-cell precursor.