Abstract
Histologic transformation of low-grade follicular lymphoma to an aggressive-grade lymphoma occurs in 60% to 80% of patients during their clinical course. The events that drive the transformation process are poorly understood. Deregulation of the MYC gene has been implicated in a small number of cases. This observation led us to examine the molecular organization of the MYC oncogene in 38 cases of histologically transformed lymphomas that arose from follicular lymphomas, and in 18 of the initial pretransformation follicular lymphomas. In addition, we examined 58 “control” low-grade follicular lymphomas that had not yet shown evidence of histologic progression. Immunoglobulin heavy chain and light chain gene rearrangements were detected in all biopsies and rearrangements of the BCL-2 locus were seen in 36 of 38 of the transformed lymphomas (consistent with their origin from follicular lymphomas), in 18 of 18 of the pretransformation follicular lymphomas, and in 51 of 58 of the control follicular lymphomas. All 18 pretransformation follicular lymphoma specimens displayed at least one immunoglobulin gene and BCL-2 rearrangement in common with the corresponding histologically progressed lymphoma, indicating a clonal relationship between the original follicular lymphoma and the histologically transformed lymphoma. MYC rearrangements were detected in 3 of 38 (8%) transformed lymphomas and in 1 of 58 (2%) control follicular lymphomas. The latter MYC rearranged follicular lymphoma was clinically aggressive and transformed to a high- grade lymphoma that led to the death of the patient within 20 months. None of the 18 pretransformation follicular lymphomas showed MYC rearrangement, including two from patients who later demonstrated MYC rearrangement in the progressed aggressive lymphoma. PvuII mutational analysis failed to identify additional MYC gene abnormalities in the progressed lymphomas. Because the Epstein-Barr virus (EBV) is associated with a fraction of high-grade lymphomas and is known to upregulate BCL-2, we looked for a potential role for this agent in our progressed lymphomas. We did not detect viral sequences in any case indicating that EBV does not play a major role in progression. The presence of MYC rearrangements in a small fraction of progressed aggressive lymphomas, and not in the corresponding antecedent follicular lymphomas, suggests that acquisition of a MYC rearrangement is in some cases associated with the transformation event.
