Nasser Z. Parsa

Cytogenetic analysis of 363 consecutively ascertained diffuse large B-cell lymphomas.

Cytogenetic analysis was performed on 363 biopsy specimens with histologically confirmed diffuse large B‐cell lymphoma (DLBCL), consecutively ascertained at the Memorial Sloan‐Kettering Cancer Center, New York, between 1984 and 1994. Among 248 samples successfully karyotyped, clonal chromosomal abnormalities were noted in 215 (87%). The salient cytogenetic features of DLBCL from this analysis comprised the following. Breakpoints clustered, in decreasing frequency, at 10 recurring sites: 14q32, 18q21, 1q21, 3q27, 1p36, 8q24, 3p21, 6q21, 1p22, and 22q11. Of these, deletion breaks affecting bands 3p21 and 1p22 and translocation breaks affecting bands 14q32, 3q27, and 1q21 were frequent and distinctive for this subset of lymphomas. Translocations affecting band 14q32 were noted in 110 cases (51%) of which 42 (20%) had t(14;18)(q32;q21), 21 (10%) had t(8;14)(q24;q32) or t(8;22)(q24;q11), 14 (6.5%) had t(3;14)(q27;q32) or t(3;22)(q27;q11), and 33 (15%) had other rearrangements of 14q32. Among 144 new translocations detected in the entire group, the breakpoints in 19 were recurrent and clustered at three sites: 1q21, 3q27, and 14q32. Regions of common cytogenetic deletions were identified at 11 sites, 1p36, 1p33–34, 1p31, 1q32, 3p25–26, 3p21, 3q21, 6q15, 6q21, 6q23–24, and 7q32, suggesting possible loss of candidate tumor suppressor genes associated with DLBCL development. Of these, only those at 6q21, 6q23, and 7q32 have previously been described in lymphoid neoplasms. The group of DLBCL with translocations affecting band 14q32 showed a significantly different pattern of additional cytogenetic changes compared to the group lacking such translocation. This new comprehensive cytogenetic characterization provides the basis for investigations aimed at identifying molecular mechanisms as well as the clinical impact of cytogenetic changes in DLBCL. Genes Chromosomes Cancer 25:123–133, 1999.

Involvement of BCL6 in chromosomal aberrations affecting band 3q27 in B‐cell non‐Hodgkin lymphoma

Chromosomal band 3q27 exhibits recurring and nonrecurring translocations and other rearrangements in approximately 8% of B‐cell non‐Hodgkin lymphomas (NHL) belonging to low‐grade as well as diffuse aggressive histologies. The BCL6 gene, which encodes a zinc‐finger transcription repressor protein and which maps to chromosomal band 3q27, is deregulated in t(3;14)(q27;q32) and other translocations by substitution of its transcription regulatory sequences by those of genes on the partner chromosomes. To delineate the cytogenetics and investigate the nature and consequence of BCL6 involvement in the spectrum of 3q27 aberrations seen in NHL, we analyzed a panel of 53 NHL tumors with 3q27 aberrations for BCL6 gene rearrangements and a subset of 32 of these for mutations. We identified four new recurring translocations involving 3q27, in addition to the previously recognized t(3;14)(q27;q32) and its variant, t(3;22)(q27;q11). Histologically, the 3q27 breaks were represented by 4% mantle cell lymphomas, 38% follicular center cell lymphomas, and 58% diffuse large B‐cell lymphomas. Approximately 50% of the tumors exhibited BCL6 rearrangements, whereas 87.5% showed mutations in the 5′ noncoding region which contains the transcription regulatory sequences. These results demonstrate that a substantial proportion of cytogenetically detected 3q27 breaks in NHLs do not represent BCL6‐associated translocations. They also suggest alternate breakpoints which may lead to BCL6 deregulation, or involvement of other genes in 3q27 translocations. The frequent BCL6 mutation in these tumors is consistent with our previous observation of hypermutation of the 5′ noncoding region of the gene in lymphomas arising in the germinal‐center B‐cells. Genes Chromosomes Cancer 23:323–327, 1998.

Bcl6 Gene Rearrangement and Other Cytogenetic Abnormalities in Diffuse Large Cell Lymphoma

Evidence for rearrangement of the BCL6 gene at 3q27 has been documented in 20-30% diffuse lymphomas with a large cell component (DLLC), and was found to be of prognostic significance at the time of diagnosis. To incorporate these observations into current cytogenetic and clinical prognostic models, 76 cases of DLLC with known BCL6 status were analyzed. Cytogenetic indicators of progression, including trisomy 7, trisomy 12, del(6)(q21q25), and structural alterations of 17p were less frequent in BCL6 rearranged DLLC compared to BCL6 germline tumors. Despite a 93% overall survival at median follow-up of 30 months, a trend for continued relapse resulted in a projected freedom from progression for the BCL6 rearranged cohort of 66% at 4 years, compared to 39% for the BCL6 germline cohort. Six cases among the BCL6 rearranged group lacked additional cytogenetic indicators of progression and remained free of disease at follow-up in excess of 7 years, whereas BCL6 rearranged cases with increasing numbers of cytogenetic aberrations showed decreased intervals free from progression of disease. These results suggest that BCL6 rearrangement should be combined with other known clinical and cytogenetic indicators in prognostic analyses of patients with DLLC.

Gene amplification in non-Hodgkin's lymphoma

Summary. Among 426 consecutively ascertained and karyotypically abnormal non‐Hodgkins lymphoma (NHL) tumours, cytological evidence for gene amplification in the form of homogeneously staining regions (HSRs) was encountered in nine cases of large cell diffuse lymphoma (LC‐DL). The mean age of patients with HSRs was 62·9 years and four died within a year of diagnosis. To identify candidate gene(s) amplified in these tumours, we performed a Southern blot analysis of tumour DNA using probes for 23 known protooncogenes and the multidrug resistance gene, PGY1, Besides a two‐fold amplification of the BCL2 gene in two cases, no evidence for overt amplification of any of the genes assayed was found. To confirm DNA amplification in these specimens we performed the DNA in‐gel renaturation assay. Evidence for presence of amplified DNA fragments was obtained in four of seven specimens. These results suggest amplification of a novel gene(s). To our knowledge, this is the first formal study of gene amplification in a large consecutively ascertained series of fresh lymphoma biopsies.