Analysis of chromosomal copy number changes and oncoprotein expression in primary central nervous system lymphomas: frequent loss of chromosome arm 6q

Primary central nervous system lymphoma (PCNSL) is a rare disease. A small number of cytogenetic studies of PCNSL have been conducted and several reports have been published on associated molecular and protein expression data. We combined these approaches in a series of eight PCNSL cases, analyzing the chromosomal abnormalities using comparative genomic hybridization (CGH), testing for Epstein Barr virus (EBV) involvement by in situ hybridization for EBER, assessing expression of p53, Bcl-2, Bcl-6 and CD10 by means of immunohistochemistry, and screening for mutations of the TP53 gene by DGGE. TP53 gene mutations and EBV expression were not detected. Most of the cases showed p53, Bcl-6 and Bcl-2 protein expression. CGH revealed DNA copy number changes in all eight cases. The most frequent changes were gains of chromosome 12 (63%), chromosome 18 (50%) and 20q (38%), and loss of chromosome arm 6q (75%). No correlation between protein expression and chromosomal abnormalities was found in these eight cases. Although gains of chromosome 12, 18 and 20q and loss of 6q have also been reported in systemic diffuse large B-cell lymphomas, the frequency of 6q deletion is clearly higher in PCNSL. This creates a similarity to primary lymphomas of the testes that also frequently have deletions of 6q. This suggests that suppressor genes located on chromosome 6q may play a role in the development of lymphomas at immunoprivileged sites, like the CNS.     

Interphase fluorescence in situ hybridization analysis of del(11)(q23) and del(17)(p13) in chronic lymphocytic leukemia. a study of 40 early-onset patients

Although B-cell chronic lymphocytic leukemia (B-CLL) is the most common form of leukemia in Western countries, little is known about its underlying molecular abnormalities and their prognostic significance, particularly for use in early therapeutic interventions in young patients. As TP53 tumor suppressor gene abnormalities and 11q23 deletions are reported to be prognostically adverse in hematologic malignancies, we used interphase fluorescence in situ hybridization to analyze their incidence and prognostic significance in young B-CLL patients. Bone marrow samples from 40 untreated B-CLL patients at diagnosis were studied using five yeast artificial chromosome clones from the 11q23.1 approximately q23.3 chromosomal region and a probe specific for the 17p13.1 locus. Twenty-three patients (58%) carried 11q deletions. Interestingly, 16 of 17 patients (94%) who showed early disease progression exhibited this chromosomal abnormality, suggesting that 11q deletions may help to identify more aggressive disease in early stage patients. In contrast, monoallelic TP53 deletions were found in all of the patients. The TP53 and 11q deletions were only present in a proportion of the clonal B-cells, which suggests that they are secondary events in B-CLL.     

Localization of the chromosome 22 breakpoints in two cases of acute megakaryoblastic leukemia with t(1;22)(p13;q13)

We describe a 54-year-old man with CD2, CD7, and CD56-positive but CD3, CD4, and CD8-negative aggressive NK cell lymphoma/leukemia. Chromosome analysis of the peripheral blood cells showed clonal aberration consisting of 46,XY,dup(3)(p21p25),der(3)t(1;3)(q12;p25),del(5)(q13q22), del(6)(q13),del(13)(q12q14). The peripheral blood lymphoma cells contained clonal EBV-DNA by Southern blot analysis. The disease was refractory to chemotherapy and the clinical course was aggressive and rapid. Deletion 6q and deletion 13q have been frequently reported in NK cell lymphoma/leukemia. Thus, some tumor suppressor genes involving NK cell malignancies may be present in these regions.     

Chromosome aberrations in B-cell chronic lymphocytic leukemia: reassessment based on molecular cytogenetic analysis

In B-cell chronic lymphocytic leukemia (B-CLL) clonal chromosome aberrations are detected in approximately 40–50% of tumors when using conventional chromosome banding analysis. Most studies find trisomy 12 to be the most frequent chromosome aberration, followed by structural aberrations of the long arm of chromosomes 13 and 14. Trisomy 12 and the ”14q+” marker are associated with shorter survival times, while the patients with 13q abnormalities have a favorable outcome, similar to those with a normal karyotype. The development of molecular cytogenetic techniques has greatly improved our ability to detect chromosome aberrations in tumor cells. Using fluorescence in situ hybridization, chromosome aberrations can be detected not only in dividing cells but also in interphase nuclei, an approach referred to as interphase cytogenetics. The prevalence of specific aberrations in B-CLL is currently being reassessed by interphase cytogenetics. By far the most frequent abnormality are deletions involving chromosome band 13q14, followed by deletions of the genomic region 11q22.3-q23.1, trisomy 12, deletions of 6q21-q23, and deletions/mutations of the TP53 tumor suppressor gene at 17p13. The evaluation of the true incidence of these aberrations now provides the basis for more accurate correlations with clinical characteristics and outcome. Deletions/mutations of the TP53 gene have been shown to be associated with resistance to treatment and to be an independent marker for poor survival. 11q deletions have been associated with extensive nodal involvement, rapid disease progression, and short survival times. Whether trisomy 12, 13q14, and 6q deletions have a prognostic impact awaits further study. The application of these molecular cytogenetic techniques will also contribute to the identification of the pathogenetically relevant genes that are affected by the chromosome aberrations in B-CLL. Received: 2 February 1998 / Accepted: 31 March 1998     

A biological role for deletions in chromosomal band 13q14 in mantle cell and peripheral t-cell lymphomas?

Structural aberrations of chromosomal band 13q14 are frequent in B-cell chronic lymphocytic leukemia (B-CLL) and target a putative tumor suppressor gene in the genomic region between the RB1 gene and the genetic marker D13S25. Recently, it has been suggested that alterations of this particular region might also be of relevance for the pathogenesis of mantle cell lymphomas (MCL). We applied dual-color fluorescence in situ hybridization (FISH) using probes for the RB1 and/or D13S25 loci and screened a total of 236 B- and T-cell non-Hodgkin's lymphomas (NHL) for deletions occurring in this genomic region. In MCL, the high rate (12/32; 38%) of hemizygous deletions and especially a deletion pattern similar to B-CLL in four of the cases provide further evidence that a substantial proportion of MCL cases may share a common way of pathogenesis with B-CLL. In other B-cell NHL, the frequency of allelic loss affecting 13q14 was overall low. However, the finding of 13q14 microdeletions in seven cases without detectable alterations of chromosome 13 at G-banding analysis might indicate a possible involvement of this genetic region also for the lymphomagenesis of single cases of B-cell NHL other than B-CLL and MCL. In T-cell NHL, allelic loss at 13q14 was encountered in three of 13 peripheral T-NHL, NOS. Taking into account the very limited cytogenetic data yet available in this entity, our series provides further evidence that 13q14 changes might represent one of the most frequent genetic abnormalities in T-cell NHL.     

Chromosome analyses in chronic lymphocytic leukemia and related B-cell neoplasms

Chromosome analyses were performed by routine G-banding in 29 patients with B-cell chronic lymphocytic leukemia (B-CLL), six with immunocytoma (IC), three with centroblastic-centrocytic (cb-cc) lymphoma, and one with hairy cell leukemia (HCL). Ages of the patients were between 46 and 81 years (mean, 63 years). 12-O-tetradecanoyl-phorbol-13-acetate (TPA) was used as a mitogen to stimulate leukemic B-cells in 72-hour cultures. Twenty-one patients had one or more chromosomal abnormalities; and in 13 patients, they were clonal; 18 patients had a normal karyotype. Seven patients had trisomy 12 (three B-CLL, two IC, two cb-cc lymphoma); two (B-CLL) had it as the sole abnormality. One patient with B-CLL had trisomy 18 as the sole abnormality, and one with IC had trisomy 18 in combination with trisomy 19. One patient with B-CLL had t(1;6)(p36;p21) as a clonal structural abnormality. A t(11;14)(q13;q32) was consistently observed in one patient with cb-cc lymphoma together with inv(1) (p22p36), der(4)t(4;?)(p16;?), del(6)(q13) and other variable changes. One patient with morphologically atypical B-CLL had t(1;11)(p36;q13) together with der(X)t(X;?)(q26;?), der(3)t(3;?)(q29;?), der(8)t(4;8)(q12;q24.1) and additional variable changes. Both patients with these complex karyotypes were in an advanced stage of disease (Binet stage C) and died within 3-6 months after chromosome analysis.     

Familial B-cell chronic lymphocytic leukemia: analysis of cytogenetic abnormalities, immunophenotypic profiles, and immunoglobulin heavy chain gene usage

B-cell chronic lymphocytic leukemia (B-CLL) is a heterogeneous disease that may exhibit familial clustering. We examined the cytogenetic, immunophenotypic, and VH gene usage characteristics of a family with B-CLL affecting 7 members in 3 generations. Interphase fluorescence in situ hybridization studies identified an acquired deletion of chromosome 13q14 in the leukemic cells of 6 affected members, accompanied by deletion 14q32 or trisomy 12 in 2 cases. VH gene analysis demonstrated clonal rearrangements of the VH3 gene family in 5 cases and of VH2 genes in 1 case. All 6 cases were mutated in VH2 or VH3. Two cases had a second VH1 family gene rearrangement that was unmutated. Flow cytometry performed on 5 cases showed the typical B-CLL immunophenotype; all were CD38-, but 3 expressed ZAP-70. Our findings support previous observations that familial and sporadic B-CLL cases are biologically similar and suggest that familial clusters will be useful for studying pathogenetic events in B-CLL.     

RFP2, c13ORF1, and FAM10A4 are the most likely tumor suppressor gene candidates for B-cell chronic lymphocytic leukemia

Occurrence of 13q14 deletions between D13S273 and D13S25 in B-cell chronic lymphocytic leukemia (B-CLL) suggests that the region contains a tumor suppressor gene. We constructed a PAC/cosmid contig largely corresponding to a 380-kb 13q14 YAC insert that we found deleted in a high proportion of B-CLL patients. We found seven genes by exon trapping, cDNA screening and analysis/cDNA extension of known expressed sequence tags. One appeared to originate from another region of 13q. Recent publications have focused on two of the genes that most likely do not have a tumor suppressor role. This study evaluates the remaining four genes in the region by mutation scanning and theoretical analysis of putative encoded products. No mutations suggestive of a pathogenic effect were found. The 13q14 deletions may be a consequence of an inherent instability of the region, an idea supported by our finding of a considerable proportion of AluY repeats. Deletion of putative enhancer sequences and/or genes in the region may result in an inactivation of tumor suppression by a haploinsufficiency mechanism. We conclude that RFP2, c13ORF1, and a chromosome 13-specific ST13-like gene, FAM10A4, are the most likely candidates for such a type of B-CLL TSG.     

Centroblastic lymphoma of the thyroid supervening long-lasting chronic lymphocytic leukemia (B-CLL) demonstration of biclonality by Immunohistochemical and gene rearrangement analysis

Summary A 67-year-old woman suffering since 5 years from a so far nontreated B-CLL underwent hemithyroidectomy for a rapidly enlarging tumor. Histologically, the coincidence of a centroblastic lymphoma and thyroidal infiltration by the CLL was diagnosed. Immunohistology revealed typical immunoprofils for both, B-CLL and centroblastic lymphoma on the background of B cell differentiation antigens. The bitypical immunoglobulin light chain expression — on the B-CLL cells and on the centroblasts — suggested biclonality. This was confirmed by gene rearrangement analysis of peripheral leukemia cells and tumor tissue. Thus, the final diagnosis of a primary thyroidal lymphoma of the centroblastic type (stage I_E) arising independently from a preexisting B-CLL was achieved. Consequently, the patient received local radiotherapy.In our opinion, the designation Richter's Syndrome, readily applied in the literature, is inappropriate for this tumor constellation.Abbreviations AEC 3-amino-9-ethylcarbazole - B-CLL B-chronic lymphocytic leukemia - CB centroblastic lymphoma - CD clusters of monoclonal antibodies to leucocyte differentiation antigens Supported by the Tumorzentrum Heidelberg/Mannheim     

Immunodetection of apoptosis-regulating proteins in lymphomas from patients with and without human immunodeficiency virus infection.

The expression of the apoptosis-regulating genes Bcl-2, Bcl-x, Bax, Mcl-1, and p53 analyzed in 4 cases of human immunodeficiency virus (HIV)-associated Hodgkin's disease, in 36 cases of HIV-related non-Hodgkin's lymphomas (NHLs), and in 109 cases of non-HIV-related NHLs by using immunohistochemistry. HIV-associated Hodgkin's disease samples were positive for all markers. For the HIV-related NHL samples, 36, 66, 88, 100, and 94% of the cases were Bcl-2, Bcl-x, Bax, Mcl-1, and p53 were found to be expressed in 69, 65, 82, 83, and 42%, respectively. No significant differences were observed in Bax and Mcl-1 staining between HIV-unrelated NHLs of B cell and T cell types. In contrast, Bcl-2 was positive in 66/79 (83%) and 10/30 (33%) of B cell and T cell HIV-unrelated NHLs, respectively (P2 < 0.001). Peculiar patterns were observed for hairy cell leukemia (Bax+, Bcl-2+, Mcl-1-) and for anaplastic large cell lymphoma (Bax+, Mcl-1+, Bcl-2-) in HIV-unrelated NHLs. Of interest, all cases with a positive expression of Bax were also found to express either Mcl-1 and/or Bcl-2, suggesting that Mcl-1 and Bcl-2 may counteract the pro-apoptosis function of Bax in vivo by protein-protein interaction within the tumor cell, as demonstrated previously in vitro. These results suggest that apoptosis regulation may have a role in the pathogenesis of some HIV-related and HIV-unrelated NHLs.     

The role of p53 in megakaryocyte differentiation and the megakaryocytic leukemias of Down syndrome

Sequence analysis of the p53 tumor suppressor gene was performed on diagnostic blood and bone marrow samples from nine children with Down syndrome and acute megakaryoblastic leukemia. p53 sequence alterations were not observed in any of seven cases of transient leukemia; however, samples from two of three patients with acute megakaryoblastic leukemia harbored sequence alterations. The acquisition of both mutations (Gly245Val and Arg72Pro) in the transformation from transient leukemia to overt acute megakaryoblastic leukemia suggests a functional role of mutant p53 in the evolution of this disease.     

经典型Richter综合征转化前后IgVH基因克隆重排及突变分析

目的 检测经典型Richter综合征的IgVH基因克隆重排及突变状态,分析转化前后IgVH基因的分子特征及其与预后的关系,并对可能涉及的分子机制进行初步探讨.方法 用基因扫描和测序分析IgVH基因.另外用免疫组织化学LAB-SA法检测两种肿瘤中zeta链结合蛋白激酶70(ZAP70)、p53、干扰紊调节因子(IRF)-4等可能潜在危险因子的表达,并结合随访资料进行生存率分析,筛选危险因子.结果 (1)B-CLL/DLBCL克隆相关(18/23,78.3%),克隆不相关(5/23,21.7%);(2)在16例克隆相关中,12例转化前B-CLL及转化后DLBCL携带未突变IgVH基因;(3)转化前后IgVH基因使用是非随机的,在克隆相关的病例中,B-CLL/DLBCL最常使用VH3-23、VH3-74、VH1-2,各占11.1%;(4)转化后DLBCL仅部分表达CD5(32.1%)和CD23(14.3%)及ZAP70(23.8%),绝大多数表达p53(80.6%)和IRF-4(82.6%);(5)17例转化后DLBCL患者中位生存时间为7个月;(6)统计学分析生存时间与B-CLl/DLBCL转化前后克隆相关与否、IgVH基因的突变状态、ZAP70、p53、IRF-4的表达不相关.结论 (1)转化后DLBCL中克隆相关与克隆不相关的比例为2:1;(2)克隆相关的DLBCL多由携带未突变型IgVH基因的B-CLL患者转化而来;(3)发生转化的B-CLL中IgVH基因使用的偏向性提示了抗原在转化中的可能作用;(4)转化后DLBCL与普通DLBCL在IgVH基因的使用、突变状态,免疫表型及预后的不同,提示其可能是一种新的DLBCL亚类.     

Loss of heterozygosity on chromosome 10, 13q(Rb), 17p,and p53 gene mutations in human brain gliomas.

Using the methods of restriction fragment length polymorphism (RFLP) and single strand conformation polymorphism (SSCP) analyses, we have examined 33 cases of human gliomas with various malignant grades to detect the deletions of putative tumor suppressor gene loci, chromosome 10, 13q(retinoblastoma gene, Rb), 17p, and p53 mutation. We observed loss of heterozygosity (LOH) at loci on chromosome 10 (36%), 13q(Rb) (54%), and 17p(50%) in malignant gliomas. There, however was no allelic loss on chromosome 10 and 17p in low-grade gliomas. Rb gene deletions were seen in low-grade gliomas, including oligodendroglioma and ependymoma. This finding suggests that Rb inactivation may be an early genetic event in the development and progression of gliomas. We correlated the results of LOH on chromosome 17p and p53 mutation. Among the 8 cases which showed LOH on chromosome 17p, only three cases (38%) revealed p53 mutations. Low incidence of p53 mutations in cases with chromosome 17p deletions suggests that some other tumor suppressor genes may be located on chromosome 17p.     

Identification of a novel 9 cM deletion unit on chromosome 6q23-24 in papillary serous carcinoma of the peritoneum

To define regions of deletion on chromosome 6q in papillary serous carcinoma of the peritoneum (PSCP), we analyzed 103 tumor tissues from 53 patients by using 11 polymorphic microsatellite markers spanning loci from 6q23 to 6q27. Allelic losses on 6q were observed in 42 of 53 (79.2%) cases. We identified 3 distinct regions with a high percentage (>40%) of loss of heterozygosity. The first region is located at 6q23-24 and defined by D6S311 (15 of 35 informative cases, 42.9%). Detailed deletion mapping of chromosome 6q23-24 in these tumor samples identified a novel 9 cM minimal deletion region flanked by D6S250 and ESR. The second one is located at 6q25.1-25.2 and defined by D6S448 (17 of 36 informative cases, 47.2%). A second minimal deletion region of 4 cM was flanked by D6S420 and D6S442. The third region is located at 6q27 and defined by D6S297 (9 of 19 informative cases, 47.4%). Comparing these results with our cases of advanced staged invasive serous epithelial ovarian carcinoma (SEOC), we observed that allelic losses at D6S311 (6q23) and D6S149 (6q27) were significantly higher for PSCP than for SEOC. The pattern of allelic loss at each tumor site within an individual patient was also studied. A total of 36 cases displayed allelic loss for at least 1 of multiple tumor sites, and 35 of these patients exhibited nonidentical patterns of allelic loss at various tumor sites of the same patient. Furthermore, an alternating pattern of allelic loss in the same patient was identified in 3 of 53 patients studied. These results show that allelic losses on 6q are very frequent in PSCP, and we show 2 discrete minimal deletion regions on 6q, suggesting the existence of at least 2 tumor suppressor genes within 6q that may be involved in the pathogenesis of PSCP. In addition, the finding of different patterns of allelic loss at different tumor sites within the same patient indicate a mutifocal origin in some PSCP cases. These results provide strong evidence to support our previous reports that PSCP is a multifocal disease entity.     

Dicentric (17;20)(p11.2;q11.2): an uncommon cytogenetic abnormality in myeloid malignancies

We report on two patients with myeloid disorders and complex karyotypes including a dicentric chromosome, dic(17;20)(p11.2;q11.2), resulting in the loss of most of 17p and 20q. The presence of the centromeres of chromosomes 17 and 20 in the dic(17;20), as well as the loss of TP53, were confirmed by fluorescence in situ hybridization. Deletions of 17p and 20q are recurrent abnormalities in hematologic disorders, particularly myelodysplastic syndrome and acute myeloid leukemia). However, a dic(17;20) is an uncommon finding. According to the few reports in the literature, dic(17;20) is associated with an unfavorable prognosis. The key mechanism might be the loss of TP53 as well as other tumor suppressor genes in 20q that may have a critical role in tumor genesis.     

Clinicopathologic significance of genetic alterations in hepatocellular carcinoma

Hepatocarcinogenesis may involve multiple mutations with distinctive pathogenetic and clinicopathologic significance. To test this hypothesis, 68 cases of hepatocellular carcinoma (HCC) were studied prospectively for genetic-clinicopathologic correlation. Ten pathologic characteristics were evaluated. TP53 (alias p53) gene mutation was studied by a polymerase chain reaction (PCR)-single-strand conformation polymorphism-sequencing; CDKN2B (alias p15) and CDKN2A (alias p16) gene methylation by methylation-specific PCR; and genetic imbalances by comparative genomic hybridization (CGH). TP53 gene mutations occurred in 25% of cases, more than half being codon 249 G to T transversion. Methylation of CDKN2A was frequent (61.7%); of CDKN2B, rare (5.9%). The CGH analysis showed a median of nine aberrations per case, with amplifications more frequent than deletions. Isochromosomes might be involved in about 25% of cases. Amplifications of 1q and 8q were most frequent. Clinicopathologic correlations showed that CDKN2A methylation was significantly associated with tumors arising in cirrhotic livers; amplifications of 17q was significant in multiple parameters of tumor invasiveness (size, venous invasion, poor cellular differentiation, microsatellite formation); other amplifications (1q, 6p, 10p, and 20p) were also significant in tumor invasion; and deletions (at 1p, 11q, 4q, and 14q) were significant in tumor growth. Consistent patterns of genetic alterations were defined in HCC, which might represent distinctive pathways in hepatocarcinogenesis.     

IFN-alpha stimulates proliferation and cytokine secretion of CD40-stimulated B cell chronic lymphocytic leukemia cells in vitro.

Interferon (IFN)-alpha has a therapeutic effect in several B cell malignancies, including low-grade non-Hodgkin's lymphoma (NHL), multiple myeloma, and hairy cell leukemia, whereas its efficacy in the treatment of B cell chronic lymphocytic leukemia (B-CLL) is rather limited. In the present study, we investigated the effect of IFN-alpha on the biologic functions of B-CLL cells, which were stimulated by cross-linking of the CD40 antigen. In cell samples from 16 B-CLL patients, the addition of IFN-alpha to CD40-stimulated purified B-CLL cells caused a significant increase in [3H]thymidine uptake (p < 0.003). In B-CLL cells maximally activated by CD40 cross-linking and interleukin-2 (IL-2)/IL-10, proliferation was not further enhanced or inhibited by IFN-alpha. In contrast, proliferation of normal tonsillar B cells stimulated by the combination CD40/IL-2/IL-10 was significantly inhibited by IFN-alpha. Because B-CLL activation might be enhanced by induction of the autocrine growth factor tumor necrosis factor-alpha (TNF-alpha), we investigated the effect of IFN-alpha on the secretion of B cell tropic cytokines. In fact, IFN-alpha significantly stimulated the secretion of IL-6 and TNF-alpha in CD40-activated B-CLL cells (p < 0.01). Although exogenous addition of TNF-alpha did not influence activation of CD40-stimulated B-CLL cells, neutralization of TNF-alpha by polyclonal antibodies led to a complete inhibition of CD40-mediated proliferation of B-CLL cells, suggesting that enhanced proliferation and increased cytokine production by CD40-activated B-CLL cells are independent IFN-alpha-mediated events. The studies presented here provide evidence that IFN-alpha mediates costimulatory signals in the context of T cell-mediated B-CLL cell activation.     

Expression of p53 protein in T- and natural killer-cell lymphomas is associated with some clinicopathologic entities but rarely related to p53 mutations

To determine if p53 abnormalities could be involved in the pathogenesis of T- or natural killer (NK)-cell lymphomas, we investigated 51 cases of these lymphomas for the expression of p53 and its relationship with p53 gene mutations, the expression of the p21 protein as well as the proliferative and apoptotic indices. Overexpression of p53 was found in 19 cases (37%), whereas mutations of the p53 gene were observed in only 5 of 28 tested cases. The analysis of immunohistochemical data showed some entity-related phenotypic profiles. Anaplastic large cell lymphomas showed a frequent overexpression of p53 (7/8 cases) and p21 (6/8 cases) proteins and rare p53 mutations (1/7 cases), suggesting accumulation of a functional wild type p53 protein able to induce p21 expression. Nodal peripheral T-cell lymphomas unspecified showed relatively frequent overexpression of p53 protein (5/7 cases), infrequent p21 expression (2/7 cases), and rare p53 gene mutations (1/6 cases). In angioimmunoblastic lymphomas, the common phenotype was p53-/p21- (15/17 cases), with only a few scattered p53-positive cells, which, on the basis of double staining results, were mostly Epstein-Barr virus-infected B cells. A p53 gene mutation was only found in 1 case (1/8 cases) of angioimmunoblastic lymphoma, which showed cytologic tumor progression. Mycosis fungoides showed p53 overexpression in 2 of 4 cases, including 1 case with p53 gene mutation and features of cytologic tumor progression. Nasal NK/T lymphomas showed p53 overexpression in 2 of 5 cases, 1 of which had a p53 gene mutation. Finally, all lymphoblastic T-cell lymphomas (5 cases) and gammadelta hepatosplenic T-cell lymphomas (3 cases) were negative for expression of p53 and p21 proteins. We conclude that p53 protein overexpression is a common finding in some entities of T- and T/NK-cell lymphomas, whereas a p53 gene mutation is a rare, sporadic, and rather late event associated with tumor progression in some instances. The p53/p21 expression pattern appears to be variable in T- and T/NK-cell lymphoma entities, reinforcing the concept of distinct, entity-related mechanisms of pathogenesis in these tumors.