Jane Houldsworth

Inactivation of the PRDM1/BLIMP1 gene in diffuse large B cell lymphoma

PR domain containing 1 with zinc finger domain (PRDM1)/B lymphocyte–induced maturation protein 1 (BLIMP1) is a transcriptional repressor expressed in a subset of germinal center (GC) B cells and in all plasma cells, and required for terminal B cell differentiation. The BLIMP1 locus lies on chromosome 6q21-q22.1, a region frequently deleted in B cell lymphomas, suggesting that it may harbor a tumor suppressor gene. We report here that the BLIMP1 gene is inactivated by structural alterations in 24% (8 out of 34) activated B cell–like diffuse large cell lymphoma (ABC-DLBCL), but not in GC B cell–like (n = 0/37) or unclassified (n = 0/21) DLBCL. BLIMP1 alterations included gene truncations, nonsense mutations, frameshift deletions, and splice site mutations that generate aberrant transcripts encoding truncated BLIMP1 proteins. In all cases studied, both BLIMP1 alleles were inactivated by deletions or mutations. Furthermore, most non–GC type DLBCL cases (n = 20/26, 77%) lack BLIMP1 protein expression, despite the presence of BLIMP1 mRNA. These results indicate that a sizable fraction of ABC-DLBCL carry an inactive BLIMP1 gene, and suggest that the same gene is inactivated by epigenetic mechanisms in an additional large number of cases. These findings point to a role for BLIMP1 as a tumor suppressor gene, whose inactivation may contribute to lymphomagenesis by blocking post–GC differentiation of B cells toward plasma cells.

Chemotherapy for Teratoma With Malignant Transformation

PURPOSE Teratoma with malignant transformation (MT) is a well-described entity that refers to the MT of a somatic teratomatous component in a germ cell tumor (GCT) to a histology that is identical to a somatic malignancy (eg, rhabdomyosarcoma [RMS]). Surgical resection has been the mainstay of therapy for localized transformed disease because these tumors are thought to be resistant to standard treatment. We report that chemotherapy has a role in selected patients with MT, determined by cell type. PATIENTS AND METHODS Chemotherapy was administered to 12 patients with MT of GCT limited to a single cell type (two patients with primitive neuroectodermal tumors, five with undifferentiated RMS, one with anaplastic small-cell tumor, two with adenocarcinoma, and two with leukemia); 10 patients had measurable disease. GCT origin was confirmed by molecular cytogenetics in five patients. Each patient received chemotherapy regimens based on the specific malignant cell observed in the transformed histology. RESULTS Seven patients with measurable disease achieved a partial response, with the duration of response ranging between 1 month and 7 years. Three of those patients are alive. Three patients did not respond to treatment, and all of those patients died as a result of their disease. CONCLUSION Chemotherapy for MT limited to a single cell type may result in major responses and long-term survival in selected patients. Local therapy after chemotherapy is an important component of treatment to achieve maximum response.

Human male germ cell tumor resistance to cisplatin is linked to TP53 gene mutation.

Male germ cell tumors (GCTs) are uniquely sensitive to cisplatin-based chemotherapy, with more than 90% of newly diagnosed cases cured. The underlying cause for resistance to treatment in 20–30% of metastatic lesions remains to be identified. Unlike other solid tumors, no mutations in the TP53 gene have been identified to date in random panels of GCT specimens, which could account for the exquisite sensitivity of these tumors to genotoxic insult. However, in a panel of resistant GCTs that did either not respond to cisplatin-based chemotherapy or subsequently relapsed and resulted in the death of the patient, we have now identified a subset of tumors to contain TP53 mutations within exons 6–9. A cell line derived from one of these tumors (228A) displayed the same TP53 mutation as the tumor specimen, expressed only mutant TP53 mRNA, and exhibited a relative resistance to cisplatin in vitro in comparison to a cell line (218A) derived from a responsive tumor with wild-type TP53. The resistant cell line displayed a much reduced apoptotic cell death and did not exhibit an induction of transcription of the p53-responsive genes WAF1 and MDM2 following cisplatin treatment, compared to that observed in the sensitive cell line. The levels of bax, an agonist of apoptosis, were found to be reduced in the resistant cell line. The simplest explanation for the resistance of this subset of GCTs that are resistant to cisplatin-based chemotherapy, is the inability of the cells to mount an apoptotic response following exposure due to a functionally inactivating mutation in the TP53 gene.

Role of promoter hypermethylation in Cisplatin treatment response of male germ cell tumors

BackgroundMale germ cell tumor (GCT) is a highly curable malignancy, which exhibits exquisite sensitivity to cisplatin treatment. The genetic pathway(s) that determine the chemotherapy sensitivity in GCT remain largely unknown.ResultsWe studied epigenetic changes in relation to cisplatin response by examining promoter hypermethylation in a cohort of resistant and sensitive GCTs. Here, we show that promoter hypermethylation of RASSF1A and HIC1 genes is associated with resistance. The promoter hypermethylation and/or the down-regulated expression of MGMT is seen in the majority of tumors. We hypothesize that these epigenetic alterations affecting MGMT play a major role in the exquisite sensitivity to cisplatin, characteristic of GCTs. We also demonstrate that cisplatin treatment induce de novo promoter hypermethylation in vivo. In addition, we show that the acquired cisplatin resistance in vitro alters the expression of specific genes and the highly resistant cells fail to reactivate gene expression after treatment to demethylating and histone deacetylase inhibiting agents.ConclusionsOur findings suggest that promoter hypermethylation of RASSF1A and HIC1 genes play a role in resistance of GCT, while the transcriptional inactivation of MGMT by epigenetic alterations confer exquisite sensitivity to cisplatin. These results also implicate defects in epigenetic pathways that regulate gene transcription in cisplatin resistant GCT.

Similar patterns of genomic alterations characterize primary mediastinal large-B-cell lymphoma and diffuse large-B-cell lymphoma.

To address the possible genetic relationship between primary mediastinal large‐B‐cell lymphoma (PMLBCL) and diffuse large‐B‐cell lymphoma (DLBCL), we compared DNA copy number changes identified by comparative genomic hybridization (CGH) analysis of 40 PMLBCL and 91 DLBCL tumors. We assessed their karyotypes by G‐banding; amplification of MYC, BCL2, and REL genes by Southern blotting; and incidence of nonpolymorphic BCL6 mutations by single‐strand conformation polymorphism analysis (SSCP). Overall, CGH identified overlapping and nonoverlapping patterns of DNA copy number changes in the two groups. Among the latter changes, gains of chromosomes 8, 11, 15, and 16 and losses of chromosomes 5, 10, 15, 16, 17, and 20 were seen only in DLBCL, and gains of chromosomes 10, 21, and 22 and losses of chromosomes 11, 13, and 18 were seen only in PMLBCL. Several overlapping changes were identified in both groups, with variation in incidence. Statistical analysis of these changes showed significant gains of chromosomes 3 (P ≤ 0.05) and 7q (P ≤ 0.05) in DLBCL and gains of chromosomes 9 (P ≤ 0.05) and 19 (P ≤ 0.05) and the X chromosome (P ≤ 0.05) and loss of chromosome 4 (P ≤ 0.05) in PMLBCL. Frequent recurring DNA amplification at 2p13‐15 and less frequent amplification at 6p21, 12q13, and 18q21 were noted in both groups. Recurring amplification at 1q21 was seen only in DLBCL, whereas nonrecurring amplification at 10p11.2 and 15q22‐24 was seen only in PMLBCL. G‐banded karyotype analysis identified t(3;14)(q27;q32) in one and t(14;18)(q32;q21) in two cases of PMLBCL. Seven of 13 cases exhibited SSCP variants in the 5′ noncoding region of BCL6. In addition, 19 of 24 PMLBCLs assayed for BCL6 protein expression by immunohistochemistry showed positive results, indicating an origin from a germinal center (GC)–derived B cell. Based on these data, we conclude that PMLBCL is a distinct entity among GC‐derived high‐grade DLBCLs.

Biology and Genetics of Adult Male Germ Cell Tumors

Adult male germ cell tumors (GCTs) arise by transformation of totipotent germ cells. They have the unique potential to activate molecular pathways, in part mimicking those occurring during gametogenesis and normal human development, as evidenced by the array of histopathologies observed in vivo. Recent expression profiling studies of GCTs along with advances in embryonic stem-cell research have contributed to our understanding of the underlying biology of the disease. Gain of the short arm of chromosome 12 detected in almost all adult GCTs appears to be multifunctional in germ cell tumorigenesis on the basis of the observed overexpression of genes mapped to this region involved in maintenance of pluripotency and oncogenesis. Expression signatures associated with the different histopathologies have yielded clues as to the functional mechanisms involved in GCT invasion, loss of pluripotency, and lineage differentiation. Genomic and epigenomic abnormalities that contribute to or cause these events have been identified by traditional genome analyses and continue to be revealed as genome-scanning technologies develop. Given the high sensitivity of most GCTs to cisplatin-based treatment, these tumors serve as an excellent model system for the identification of factors associated with drug resistance, including differentiation status and acquisition of genomic alterations. Overall, adult male GCTs provide a unique opportunity for the examination of functional links between transformation and pluripotency, genomic and epigenomic abnormalities and lineage differentiation, and the identification of genetic features associated with chemotherapy resistance.

Gene expression-based classification of nonseminomatous male germ cell tumors

Male adult germ cell tumors (GCTs) comprise two major histologic groups: seminomas and nonseminomas. Nonseminomatous GCTs (NSGCTs) can be further divided into embryonal carcinoma (EC), teratoma (T), yolk sac tumor (YS), and choriocarcinoma (CC) on the basis of the lineage differentiation that they exhibit. NSGCTs frequently present as mixed tumors consisting of two or more histological subtypes, often limiting correlative studies of clinical and molecular features to histology. We sought to develop a molecular classifier that could predict the predominant histologic subtype within mixed NSGCT tumor samples. The expression profiles of 84 NSGCTs (42 pure and 42 mixed) and normal age-matched testes were obtained using Affymetrix microarrays. Using prediction analysis for microarrays, we identified 146 transcripts that classified the histology of pure NSGCTs samples with 93% accuracy. When applied to mixed NSGCTs, the classifier predicted a histology that was consistent with one of the reported components in 93% of cases. Among the predictive transcripts were CGB (high in CC), LCN2 (high in T), BMP2 (high in YS), and POU5F1 (high in EC). Thus, the expression-based classifier accurately assigned a single predominant histology to mixed NSGCTs, and identified transcripts differentially expressed between histologic components with relevance to NSGCT differentiation.

Identification and Validation of a Gene Expression Signature That Predicts Outcome in Adult Men With Germ Cell Tumors

PURPOSE Germ cell tumor (GCT) is the most common malignancy in young adult men. Currently, patients are risk-stratified on the basis of clinical presentation and serum tumor markers. The introduction of molecular markers could improve outcome prediction. PATIENTS AND METHODS Expression profiling was performed on 74 nonseminomatous GCTs (NSGCTs) from cisplatin-treated patients (ie, training set) and on 34 similarly treated patients with NSGCTs (ie, validation set). A gene classifier was developed by using prediction analysis for microarrays (PAM) for the binary end point of 5-year overall survival (OS). A predictive score was developed for OS by using the univariate Cox model. RESULTS In the training set, PAM identified 140 genes that predicted 5-year OS (cross-validated classification rate, 60%). The PAM model correctly classified 90% of patients in the validation set. Patients predicted to have good outcome had significantly longer survival than those with poor predicted outcome (P < .001). For the OS end point, a 10-gene model had a predictive accuracy (ie, concordance index) of 0.66 in the training set and a concordance index of 0.83 in the validation set. Dichotomization of the samples on the basis of the median score resulted in significant differences in survival (P = .002). For both end points, the gene-based predictor was an independent prognostic factor in a multivariate model that included clinical risk stratification (P < .01 for both). CONCLUSION We have identified gene expression signatures that accurately predict outcome in patients with GCTs. These predictive genes should be useful for the prediction of patient outcome and could provide novel targets for therapeutic intervention.

The cytogenetic theory of the pathogenesis of human adult male germ cell tumors

Human male germ cell tumors (GCTs) represent a biological paradox because, in order to develop into a pluripotential tumor, a germ cell destined to a path of limited or no proliferation must acquire the potential for unlimited proliferation. In addition, it must acquire the ability to elicit embryonal differentiation patterns without the reciprocal inputs from fertilization and the imprinting‐associated genomic changes which are a part of normal embryonal development. Although much speculated about, the genetic mechanisms underlying these properties of male GCTs remain enigmatic. Recent cytogenetic and molecular genetic analyses of these tumors are providing new insights and new testable hypotheses. Based on our recent work, we propose two such hypotheses. One relates to the mechanism of germ cell transformation and germ cell tumor development. We suggest that the invariable 12p amplification noted as early as in carcinoma in situlintratubular germ cell neoplasia (CIS/ITGCN) lesions leads to deregulated overexpression of cyclin D2, a cell cycle G1/S checkpoint regulator with oncogeneic potential. Such overexpression reinitiates the cell cycle. We visualize this happening during the pachytene stage of meiosis through aberrant recombinational events which lead to 12p amplification. The other hypothesis relates to the origin of primary extragonadal GCTs. By comparing cytogenetic changes in primary mediastinal versus gonadal lesions, we propose that, in contrast to long‐standing speculation that primary extra‐gonadal tumors arise from embryonally misplaced primordial germ cells, these lesions arise from migration of transformed gonadal germ cells.

Testicular mixed germ cell tumors: a morphological and immunohistochemical study using stem cell markers, OCT3/4, SOX2 and GDF3, with emphasis on morphologically difficult-to-classify areas

Stem cell markers, OCT3/4, and more recently SOX2 and growth differentiation factor 3 (GDF3), have been reported to be expressed variably in germ cell tumors. We investigated the immunohistochemical expression of these markers in different testicular germ cell tumors, and their utility in the differential diagnosis of morphologically difficult-to-classify components of these tumors. A total of 50 mixed testicular germ cell tumors, 43 also containing difficult-to-classify areas, were studied. In these areas, multiple morphological parameters were noted, and high-grade nuclear details similar to typical embryonal carcinoma were considered ‘embryonal carcinoma-like high-grade’. Immunohistochemical staining for OCT3/4, c-kit, CD30, SOX2, and GDF3 was performed and graded in each component as 0, negative; 1+, 1–25%; 2+, 26–50%; and 3+, >50% positive staining cells. The different components identified in these tumors were seminoma (8), embryonal carcinoma (50), yolk sac tumor (40), teratoma (40), choriocarcinoma (3) and intra-tubular germ cell neoplasia, unclassified (35). By immunohistochemistry, the staining patterns were OCT3/4 −3+, all seminomas, embryonal carcinomas and intra-tubular germ cell neoplasia; SOX2 −3+, all embryonal carcinomas and −2 to 3+, 11/14 (79%) primitive neuroectodermal components in immature teratomas; GDF3 −2 to 3+, all yolk sac tumors, seminomas and intra-tubular germ cell neoplasia and 1 to 2+, 40/50 embryonal carcinomas. A total of 34/43 (79%) of difficult-to-classify areas stained 3+ for OCT3/4, CD30, and SOX2, similar to embryonal carcinoma. Among these areas, only ‘embryonal carcinoma-like high-grade’ nuclear details were significantly associated with such an immunophenotype. Thus, SOX2 is expressed in embryonal carcinoma and primitive neuroectoderm of teratoma, and unlike OCT3/4, not in intra-tubular germ cell neoplasia and seminoma. Therefore, it may be useful in the distinction of seminoma from embryonal carcinoma, and potentially in diagnosing early carcinomatous differentiation in seminoma. GDF3 positivity, in the absence of OCT3/4 and CD30, combined with morphological features, is helpful in the diagnosis of yolk sac tumor. ‘Embryonal carcinoma-like high-grade’ nuclear details are the most important morphological criterion for the diagnosis of embryonal carcinoma in difficult-to-classify areas.