The majority of low-grade follicular lymphomas will eventually transform to an aggressive intermediate, or high-grade lymphoma. The molecular mechanisms responsible for this transformation have not been determined. We studied serial biopsies from 34 patients with follicular lymphomas that underwent histologic transformation, for abnormalities of the p53 tumor suppressor gene by a combination of immunohistochemistry, single strand conformation polymorphism analysis (SSCP), and sequencing. We found overexpression of p53 in 10 of the 34 transformed aggressive lymphomas, 9 of which contained mutations identified by SSCP analysis and subsequent sequencing. Matched pretransformation low-grade follicular lymphoma biopsies were available for 7 of the 10 cases. None of six studied by immunohistochemistry showed overexpression of p53 and only 1 of 4 studied by SSCP/sequencing showed the presence of mutation in the pretransformation biopsy. Interestingly, an eighth p53 positive transformed lymphoma recurred with a clonally related, p53 negative low-grade lymphoma 5 years after the patient had achieved a complete remission. Immunohistochemistry also showed that several pretransformation biopsies from p53 positive transformed cases showed rare p53 positive cells and in one case we could document an increase in their number over time. Twenty-five additional low-grade follicular lymphoma biopsies were also examined. Three patients had lymphomas positive for p53 mutation. One of the three subsequently transformed within a year of the biopsy studied; the second patient had an earlier (unavailable) biopsy at a different site that showed transformed histology. The third patient was treated with ProMACE-MOPP combination chemotherapy and attained a complete remission. We conclude that (1) mutations of p53 are associated with histologic transformation in approximately 25% to 30% of follicular lymphomas and (2) p53 positive cells can be detected before histologic transformation, but do not comprise a significant percentage of the neoplastic cell population (identifiable by SSCP) until late in the disease, just before or after histologic progression. Finally, the data also suggest that p53 positive low-grade lymphomas are at risk for progression and that in this subset, aggressive therapy may be warranted.

The LAZ3 gene encodes a novel zinc-finger protein that shares homology with several Drosophila transcription factors. This gene was identified by its disruption in translocations involving chromosome 3q27 in diffuse large-cell lymphomas. To assess the frequency and role of this gene's involvement in lymphomagenesis and tumor progression, we examined a series of 170 cases of non-Hodgkin's lymphomas of B-cell lineage for LAZ3 gene rearrangement, expression, and mutation. The cases included 35 de novo diffuse aggressive lymphomas (DAL; 19 large-cell, 4 mixed-cell, and 12 large-cell immunoblastic), 52 transformed aggressive lymphomas derived from follicular lymphomas (TFL), 42 indolent follicular lymphomas (FL), 14 mantle cell lymphomas (MCL), and 27 small noncleaved cell lymphomas (SNCL). LAZ3 rearrangements were found in 10 DAL (28.6%), 9 TFL (17.3%), and 6 FL (14.3%), but not in any of the SNCL or MCL. LAZ3 rearrangement was not exclusive of bcl-2 rearrangement. Most rearrangement breakpoints mapped to a 10-kb BamHI-Xba I fragment located 5′ to the LAZ3 coding sequence, consistent with previously reported breakpoint locations. Northern analysis of both rearranged and nonrearranged B-cell lymphoma cases showed similar levels of a transcript of approximately 3.8 kb, indicating that LAZ3 is broadly expressed in B-cell tumors and is not confined to rearranged cases. To investigate whether mutation of the LAZ3 gene might contribute to a potential role for this gene in lymphomagenesis, we screened the coding sequences of 13 rearranged cases, 6 nonrearranged cases, and 13 hematopoietic tumor cell lines. Although three probable polymorphisms were identified, mutations were detected in only 2 rearranged cases. Only 1 of these resulted in an amino acid substitution. Two cell lines (SU-DHL4 and Molt-4) also contained mutations; only one resulted in an amino acid substitution. We conclude (1) that LAZ3 rearrangements occur in a significant fraction of de novo DAL as well as in a smaller subset of indolent and transformed follicular lymphomas; (2) that LAZ3 message is expressed in both rearranged and nonrearranged B-cell lymphomas; and (3) that mutation of the LAZ3 gene does not contribute to its putative oncogenic role in most 3q27 translocated B-cell lymphomas.

We have examined 107 cases of B-cell lymphoma for the t(14;18) translocation, characteristically described in follicular lymphoma. B-Cell lymphomas of extranodal origin, and in particular malignancies derived from mucosa-associated lymphoid tissue (MALT), were compared with node-based lymphomas of follicular and diffuse morphology. Cytogenetic techniques were supplemented by molecular analysis using probes which recognize both the major and the minor breakpoint regions of the bcl-2 gene located on chromosome 18 (q21). t(14;18) was detected in 55 per cent of follicular and 27 per cent of diffuse B-cell lymphomas thought to be of follicle centre cell origin. Cytogenetics and molecular analysis proved equally effective in demonstrating the translocation. t(14;18) was not observed in the 36 extranodal lymphomas examined, of which 20 were characterized histologically as lymphomas of MALT, using either technique. In addition, 30 cases demonstrated only a germline band when probed with a bcl-3 probe specific for t(14;19), a translocation observed in chronic lymphocytic leukaemia (CLL). Cytogenetic abnormalities were detected in all cases of extranodal lymphoma, although no consistent abnormality was observed. Numerical abnormalities of chromosomes 3, 6, 16, and 18; structural abnormalities of chromosomes 2, 6, 8, and 9; and small marker chromosomes were frequently seen. This study provides data which suggest that different genetic events are involved in the development of lymphoma of MALT from those giving rise to follicle centre cell lymphomas.