BACKGROUNDc-MYC/BCL2 HGBL DH, c-MYC/BCL6 HGBL DH and HGBL NOS are different entities that are represented in some cases by transformed from low-grade lymphomas (tLGLs): follicular (FL) or marginal zone lymphoma (MZL).AIMSTo distinguish the group of tLGLs from de novo HGBLs.METHODSWe have analyzed the data of 99 HGBL patients: 6-HGBL TH, 26-c-MYC/BCL2 HGBL DH, 16-c-MYC/BCL6 HGBL DH and 51-HGBL NOS. We suggested an integral transformation index (ITI) indicating the probability of HGBLs development from tLGLs. It included: histologic signs of transformation (HST), lymphoma history ≥4 months, discordant bone marrow involvement, paraprotein secretion, and minimal disseminated disease in blood by flow cytometry. Comparison of groups was carried out using χ2 test. Differences were considered significant at p<0.05 (STATISTICA 12.0).RESULTSMorphological signs of tLGLs were revealed in 3 patients with HGBL TH, 11 patients with c-MYC/BCL2 HGBL DH (from FL), 6 patients with c-MYC/BCL6 HGBL DH (from MZL), and 4 of patients with HGBL NOS (1 from FL and 3 from MZL). ITI increased probability to reveal tLGLs among HGBLs compared with morphological study only from 8% to 67% among HGBL NOS (p=0.001), from 42% to 62% among c-MYC/BCL2 HGBL DH, from 38% to 81% among c-MYC/BCL6 HGBL DH (p=0.01) and from 50% to 83% among HGBL TH. c-MYC/BCL2 HGBL DH and HGBL TH predominantly attended to GCB-subtype (93%), c-MYC/BCL6 HGBL DH to non-GCB (54%), (p=0.03). ITI score at least 1 point correlated with central nervous system (CNS) involvement (p=0.008). Paraprotein secretion was observed only in c-MYC/BCL6 HGBL DH or HGBL NOS patients.CONCLUSIONSITI distinguishes cases of tLGLs among HGBLs. c-MYC/BCL2 HGBL DH and HGBL TH are frequently presented by GCB-lymphomas transformed from FL. c-MYC/BCL6 HGBL DH and HGBL NOS can develop from MZL with paraprotein secretion. Involvement of the CNS is characteristic of tLGLs.