Candidate regions for testicular cancer susceptibility genes

Could Aberrant Migration Explain Metachronous Germ Cell Tumors?

BACKGROUND

Extragonadal germ cell tumors (GCTs) are thought to arise as a result of local transformation of primordial gonadal cells (PGCs) that become misplaced during embryogenesis. With the exception of bilateral testis tumors, metachronous GCT (i.e., occurring at a site classically described for primary GCTs) are rare events.

PATIENTS AND METHODS

The clinical, radiological, and molecular data (if available) of patients with metachronous GCT were analyzed.

RESULTS

Three Caucasian males were identified: case 1 presented with a pineal germinoma 19 years after a mediastinal seminoma that had been treated with chemotherapy, case 2 presented with a pineal non-seminomatous GCT (NSGCT) that occurred three years after a mediastinal seminoma treated with chemotherapy, and case 3 presented with a mediastinal seminoma concomitant with a suprasellar germinoma that occurred two years after a stage I testicular NSGCT treated exclusively with surgery. None of these patients had a positive family history or disorder of sex development. Molecular data were available for cases 2 and 3. In case 2, a CHEK2 gene biallelic inactivation in the second tumor suggested chemoresistance to cisplatin. This was further confirmed by tumor progression during second-line treatment. In case 3, the molecular analysis revealed different profiles in the three tumors, thus suggesting distinct tumor cell origins.

CONCLUSION

These rare cases should alert clinicians of the possibility of multiple GCTs that should not be considered to be relapses. The underlying physiopathology is unknown, but multiple PGC mismigrations is a likely cause. Initial treatment with cisplatin may select chemo-resistant clones, thereby making the subsequent treatment more of a challenge.

A second independent locus within DMRT1 is associated with testicular germ cell tumor susceptibility

Susceptibility to testicular germ cell tumors (TGCT) has a significant heritable component, and genome-wide association studies (GWASs) have identified association with variants in several genes, including KITLG, SPRY4, BAK1, TERT, DMRT1 and ATF7IP. In our GWAS, we genotyped 349 TGCT cases and 919 controls and replicated top hits in an independent set of 439 cases and 960 controls in an attempt to find novel TGCT susceptibility loci. We identified a second marker (rs7040024) in the doublesex and mab-3-related transcription factor 1 (DMRT1) gene that is independent of the previously described risk allele (rs755383) at this locus. In combined analysis that mutually conditions on both DMRT1 single nucleotide polymorphism markers, TGCT cases had elevated odds of carriage of the rs7040024 major A allele [per-allele odds ratio (OR) = 1.48, 95% confidence interval (CI) 1.23, 1.78; P = 2.52 × 10(-5)] compared with controls, while the association with rs755383 persisted (per allele OR = 1.26, 95% CI 1.08, 1.47, P = 0.0036). In similar analyses, the association of rs7040024 among men with seminomatous tumors did not differ from that among men with non-seminomatous tumors. In combination with KITLG, the strongest TGCT susceptibility locus found to date, men with TGCT had greatly elevated odds (OR = 14.1, 95% CI 5.12, 38.6; P = 2.98 × 10(-7)) of being double homozygotes for the risk (major) alleles at DMRT (rs7040024) and KITLG (rs4474514) when compared with men without TGCT. Our findings continue to corroborate that genes influencing male germ cell development and differentiation have emerged as the major players in inherited TGCT susceptibility.

Younger age-at-diagnosis for familial malignant testicular germ cell tumor

One of the clinical hallmarks of hereditary cancer susceptibility disorders is a younger-than-usual age at diagnosis. Familial aggregation of testicular germ cell tumor (TGCT) has been reported, but data on whether familial TGCT cases are diagnosed at an earlier age are inconclusive. Here we compared the age at diagnosis of familial TGCT cases with that of population cases in several countries. Familial TGCT is defined as affected individuals from families with >or=2 cases of TGCT. Age at diagnosis of familial cases from the United States, Canada, United Kingdom, Australia and New Zealand, Norway, and Hungary was compared to cases identified in population-based cancer registries from the respective country, using the generalized estimation equation method. Age at diagnosis was statistically significantly younger for familial TGCT cases from North America (P = 0.024), the United Kingdom (P < 0.0001), and Australia and New Zealand (P = 0.0033) compared with population cases. When stratified by histology, the difference in age at diagnosis distribution between familial and population cases was observed for seminoma cases from North America (P = 0.002) and the United Kingdom (P < 0.0001) and non-seminoma cases from the United Kingdom (P = 0.029) and Australia and New Zealand (P = 0.0023). In summary, we found that the age at diagnosis for familial TGCT cases is, on the average, 2-3 years younger than that for the population cases in North America, United Kingdom, and Australia and New Zealand. The younger age at diagnosis might be suggestive of a genetic basis for familial TGCT.

Biology of testicular germ cell tumors

Germ cell tumors are derived from cells of the germ cell lineage and are the most common solid malignancies to affect young Caucasian men between the ages of 15 and 40 years. All testicular germ cell tumors develop from the same precursor lesion, intratubular germ cell neoplasia unclassified, which in turn is thought to arise from malignant transformation of a primordial germ cell or gonocyte. These tumors are characterized by extreme chemosensitivity and are considered a model for curative disease. In spite of this, a small subset of patients with metastatic disease fail to achieve a complete response with cisplatin-based chemotherapy or relapse from complete remission. Understanding the molecular biology may help the design of new therapies for those patients with a poor prognosis and could also improve the treatment of cancer in general. Current understanding of the role of genetic and epigenetic factors in the etiology of germ cell tumors and the biochemical mechanisms underlying chemotherapy sensitivity and resistance is discussed in detail in this review.

Deletion of eIF2beta suppresses testicular cancer incidence and causes recessive lethality in agouti-yellow mice

The agouti-yellow (A(y)) deletion is the only genetic modifier known to suppress testicular germ cell tumor (TGCT) susceptibility in mice or humans. The A(y) mutation deletes Raly and Eif2s2, and induces the ectopic expression of agouti, all of which are potential TGCT-modifying mutations. Here we report that the reduced TGCT incidence of heterozygous A(y) males and the recessive embryonic lethality of A(y) are caused by the deletion of Eif2s2, the beta subunit of translation initiation factor eIF2. We found that the incidence of affected males was reduced 2-fold in mice that were partially deficient for Eif2s2 and that embryonic lethality occurred near the time of implantation in mice that were fully deficient for Eif2s2. In contrast, neither reduced expression of Raly in gene-trap mice nor ectopic expression of agouti in transgenic or viable-yellow (A(vy)) mutants affected TGCT incidence or embryonic viability. In addition, we provide evidence that partial deficiency of Eif2s2 attenuated germ cell proliferation and differentiation, both of which are important to TGCT formation. These results show that germ cell development and TGCT pathogenesis are sensitive to the availability of the eIF2 translation initiation complex and to changes in the rate of translation.

The International Testicular Cancer Linkage Consortium: a clinicopathologic descriptive analysis of 461 familial malignant testicular germ cell tumor kindred

OBJECTIVES

Familial aggregation of testicular germ cell tumor (TGCT) has been reported, but it is unclear if familial TGCT represents a unique entity with distinct clinicopathologic characteristics. Here we describe a collection of familial TGCT cases from an international consortium, in an effort to elucidate any clinical characteristics that are specific to this population.

MATERIALS AND METHODS

Families with >or=2 cases of TGCT enrolled at 18 of the sites participating in the International Testicular Cancer Linkage Consortium were included. We analyzed clinicopathologic characteristics of 985 cases from 461 families.

RESULTS

A majority (88.5%) of families had only 2 cases of TGCT. Men with seminoma (50% of cases) had an older mean age at diagnosis than nonseminoma cases (P = 0.001). Among individuals with a history of cryptorchidism, TGCT was more likely to occur in the ipsilateral testis (kappa = 0.65). Cousin pairs appeared to represent a unique group, with younger age at diagnosis and a higher prevalence of cryptorchidism than other families.

CONCLUSIONS

Clinicopathologic characteristics in these familial TGCT cases were similar to those generally described for nonfamilial cases. However, we observed a unique presentation of familial TGCT among cousin pairs. Additional studies are needed to further explore this observation.

Loss of the transmembrane but not the soluble kit ligand isoform increases testicular germ cell tumor susceptibility in mice

Several genetic variants act as modifiers of testicular germ cell tumor (TGCT) susceptibility in the 129/Sv mouse model of human pediatric TGCTs. One such modifier, the Steel locus, encodes the transmembrane-bound and soluble ligand of the kit receptor. Some (Sl and SlJ) but not all (Sld) mutations of the Steel locus increase TGCT incidence in heterozygous mutant mice. Because Sl and SlJ are large deletions that affect multiple transcripts and Sld is an intragenic deletion of the kit ligand (Kitl) from which only the soluble protein is produced, it was uncertain whether Kitl or a neighboring gene is a modifier of TGCT susceptibility. We tested the effect of the small Steel grizzle-belly (Slgb) deletion on TGCT susceptibility to determine whether Kitl is a TGCT modifier gene. An increase in TGCT incidence was observed in Slgb/+ heterozygotes, and fine mapping of the deletion breakpoints revealed that Kitl is the only conventional gene deleted by the mutation, suggesting that Kitl is the TGCT modifier gene at the Steel locus. Additionally, we propose that soluble KITL in Sld/+ heterozygous mutant mice complements a dosage effect of transmembrane-associated kit ligand on TGCT susceptibility and that the kit receptor (Kit) is haplosufficient for primordial germ cell development.

Testicular germ cell tumors in mice: new ways to study a genetically complex trait

Testicular germ cell tumors (TGCTs) are the most common cancer affecting young men. Although TGCTs are common and the genetic component of susceptibility is unusually strong, discovery of TGCT susceptibility genes in humans has been challenging. The 129/Sv inbred mouse strain is an important experimental model for studying the genetic control of TGCT susceptibility. It is the only inbred mouse strain with an appreciable frequency of spontaneous TGCTs. TGCTs in 129/Sv males share various developmental and histological characteristics with human pediatric TGCTs. As in humans, susceptibility in 129/Sv is a genetically complex trait that is too complex for conventional genetic approaches. However, several genetic variants, when congenic or isogenic on the 129/Sv background, act as genetic modifiers of TGCT susceptibility. Alternative experimental approaches based on these modifier genes can be used to unravel the complex genetic control of TGCT susceptibility. We discuss the application of modifier genes in genetic interaction tests and sensitized polygenic trait analyses toward the understanding of the complex genetics and biology of TGCT susceptibility in mice.

Familial testicular cancer: interest in genetic testing among high-risk family members

PURPOSE

This study is part of an ongoing National Cancer Institute multidisciplinary, etiologically-focused, cross-sectional study of Familial Testicular Cancer (FTC). The current report targets interest in clinical genetic testing for susceptibility to FTC.

METHODS

Demographics, knowledge, health beliefs, and psychological and social factors were evaluated as covariates related to interest in genetic testing.

RESULTS

The majority (66%) of 229 participants (64 affected men, 66 unaffected men, and 99 women) from 47 multiple-case FTC families expressed interest in having a genetic test within 6 months, should such a test become available. Interest was similar among the three subgroups mentioned above. Worries about insurance discrimination based on genetic test results were associated with a significantly lower interest in testing. Alternatively, participants were more likely to be interested in genetic testing if they were younger and had higher levels of family support, a physician's recommendation supporting testing, cancer distress, and a need for information to inform the health care of their children.

CONCLUSIONS

This study reveals social and relationship factors that FTC survivors and their relatives considered important when contemplating the use of new genetic technologies. This is the first study describing hypothetical interest in genetic testing for familial testicular cancer.

Testicular germ cell tumours: the paradigm of chemo-sensitive solid tumours

Testicular germ cell tumours (TGCTs) are the most frequent solid malignant tumour in men 20-40 years of age and the most frequent cause of death from solid tumours in this age group. Up to 50% of the patients suffer from metastatic disease at diagnosis. The majority of metastatic testicular cancer patients, in contrast to most other metastatic solid tumours, can be cured with highly effective cisplatin-based chemotherapy. From a genetic point of view, almost all TGCTs in contrast to solid tumours are characterised by the presence of wild type p53. High p53 expression levels are associated with elevated Mdm2 levels and a loss of p21(Waf1/Cip1) expression suggesting a changed functionality of p53. Expression levels of other proteins involved in the regulation of cell cycle progression indicate a deregulated G1-S phase checkpoint in TGCTs. After cisplatin-induced DNA damage, the increasing levels of p53 lead to the trans-activation of a number of genes but not of p21(Waf1/Cip1), preferentially directing TGCT cells into apoptosis or programmed cell death, both via the mitochondrial and the death receptor apoptosis pathways. The sensitivity of TGCTs to chemotherapeutic drugs may lay in the susceptibility of germ cells to apoptosis. Taken together, this provides TGCT as a tumour type model to investigate and understand the molecular determinants of chemotherapy sensitivity of solid tumours. This review aims to summarise the current knowledge on the biological basis of cisplatin-induced apoptosis and response to chemotherapy in TGCTs.

Enhancers and suppressors of testicular cancer susceptibility in single- and double-mutant mice

Susceptibility to spontaneous testicular germ cell tumors (TGCTs), a common cancer affecting young men, shows unusual genetic complexity. Despite remarkable progress in the genetics analysis of susceptibility to many cancers, TGCT susceptibility genes have not yet been identified. Various mutations that are inherited as Mendelian traits in laboratory mice affect susceptibility to spontaneous TGCTs on the 129/Sv inbred genetic background. We compared the frequency of spontaneous TGCTs in single- and double-mutant mice to identify combinations that show evidence of enhancer or suppressor effects. The lower-than-expected TGCT frequencies in mice with partial deficiencies of TRP53 and MGF-SLJ and in 129.MOLF-Chr19 (M19) consomic mice that were heterozygous for the A(y) mutation suggest that either these genes complement each other to restore normal functionality in TGCT stem cells or together these genes activate mechanisms that suppress incipient TGCTs. By contrast, the higher-than-expected TGCT frequencies in Mgf(Sl-J)-M19 compound heterozygous mice suggest that these mutations exacerbate each other's effects. Together, these results provide clues to the genetic and molecular basis for susceptibility to TGCTs in mice and perhaps in humans.

Chromosomes, genes, and development of testicular germ cell tumors

A literature review found 265 articles on testicular germ cell tumors (TGCTs) detailing the copy number of chromosomal regions and expression of 245 genes. An initial precursor stage, intratubular germ cell neoplasia (IGCN), is characterized by triploidization and an upregulation of KIT, ALPP, CCDN2, and ZNF354A, and a downregulation of CDKN2D. TGCT regularly have a series of chromosomal aberrations: a decrease in copy number at 4q21 approximately qter and 5q14 approximately qter; an increase at 7p21 approximately pter, 7q21 approximately q33, and 8q12 approximately q23 (especially high increase in seminoma); a decrease at 11p11 approximately p15 and 11q14 approximately q24; an increase at 12p11 approximately pter; a decrease at 13q14 approximately q31; an increase of 17q11 approximately q21 (only for nonseminoma); a decrease of 18q12 approximately qter; and an increase at 21q21 approximately qter, 22q11 approximately qter (only for seminoma), and Xq. Macroscopically overt TGCT is associated with a characteristic series of abnormalities in the retinoblastoma pathway including upregulation of cyclin D2 and p27 and downregulation of RB1 and the cyclin-dependent kinase inhibitors p16, p18, p19, and p21. TGCT thus has a synergistic pattern in gene expressions of the retinoblastoma pathway that is rare in other malignancies.

Enhancers and Suppressors of Testicular Cancer Susceptibility in Single- and Double-Mutant Mice

Susceptibility to spontaneous testicular germ cell tumors (TGCTs), a common cancer affecting young men, shows unusual genetic complexity. Despite remarkable progress in the genetics analysis of susceptibility to many cancers, TGCT susceptibility genes have not yet been identified. Various mutations that are inherited as Mendelian traits in laboratory mice affect susceptibility to spontaneous TGCTs on the 129/Sv inbred genetic background. We compared the frequency of spontaneous TGCTs in single- and double-mutant mice to identify combinations that show evidence of enhancer or suppressor effects. The lower-than-expected TGCT frequencies in mice with partial deficiencies of TRP53 and MGF-SLJ and in 129.MOLF-Chr19 (M19) consomic mice that were heterozygous for the Ay mutation suggest that either these genes complement each other to restore normal functionality in TGCT stem cells or together these genes activate mechanisms that suppress incipient TGCTs. By contrast, the higher-than-expected TGCT frequencies in Mgf Sl-J-M19 compound heterozygous mice suggest that these mutations exacerbate each other’s effects. Together, these results provide clues to the genetic and molecular basis for susceptibility to TGCTs in mice and perhaps in humans.

Genetic control of susceptibility to spontaneous testicular germ cell tumors in mice

Testicular germ cell tumors (TGCTs) are the most common cancer affecting young men. TGCT is a polygenic trait and genes that control susceptibility for TGCT development have not yet been identified. The 129/Sv inbred strain of mice is an important experimental model to study the genetics and development of TGCTs. We review several novel approaches that were developed to study the susceptibility of TGCTs in the 129/Sv mouse model and its application in humans. These approaches showed that several spontaneous and engineered mutations interact with 129/Sv-derived susceptibility genes to enhance or suppress susceptibility; two of these mutations (Ter and Trp53) revealed novel linkages for susceptibility genes in sensitized polygenic trait analysis. Linkage analysis with a chromosome substitution strains suggests that as many as 100 genes control susceptibility. Bilateral TGCTs result from the coincidental occurrence of unilateral tumors. These results highlight the important contributions that this mouse model can make to studies of TGCT susceptibility in humans.

Localisation of susceptibility genes for familial testicular germ cell tumour

Approximately 1700 men in the United Kingdom develop testicular germ cell tumours (TGCT) per year. Among the known risk factors a family history of disease remains one of the strongest (1, 2). Two-percent of TGCT cases report another affected family member. Epidemiological studies have shown that there is an eight to ten fold increase in relative risk of TGCT to brothers of patients and a fourfold increased risk to fathers and sons (2-5). This relative risk is considerably higher than for most other common cancers, which rarely exceeds four and strongly suggests that genes may play an important role in TGCT. Linkage analysis of the set of families compatible with X-linkage (i.e. no male to male transmission) provided the first statistically significant evidence for a TGCT predisposition locus (6). The gene called TGCT1 is located at Xq27 and seems to be associated with a risk of bilateral disease and undescended testis. However TGCT1 does not account for all TGCT pedigrees and additional susceptibility genes must exist. Our group has now genotyped 179 TGCT pedigrees and identified additional genomic regions that might also harbour TGCT susceptibility genes. This paper reviews the current data for the region at Xq27 and presents evidence for several other possible candidate regions.

The testicular germ cell tumour genome

Human testicular germ cell tumour (TGCT) of adolescents and young adults develop from precursor lesions called carcinoma in situ (CIS), which is believed to originate from diploid primordial germ cells during foetal life. CIS is initiated by an aneuploidisation event accompanied by extensive chromosome instability. The further transformation of CIS into invasive TGCT (seminomas and nonseminomas) is associated with increased copy number of chromosome arm 12p, most often seen as isochromosome 12p. Despite the morphological distinctions between seminomatous and nonseminomatous TGCTs, they have many of the same regional genomic disruptions, although frequencies may vary. However, the two histological subtypes have quite distinct epigenomes, which is further evident from their different gene expression patterns. CIS develops from cells with erased parental imprinting, and the seminoma genome is under-methylated compared to that of the nonseminoma genome. High throughput microarray technologies have already pinpointed several genes important to TGCT, and will further unravel secrets of how specific genes and pathways are regulated and deregulated throughout the different stages of TGCT tumourigenesis. In addition to acquiring new insights into the molecular mechanisms of TGCT development, understanding the TGCT genome will also provide clues to the genetics of human embryonic development and of chemotherapy response, as TGCT is a good model system to both.

Testicular carcinoma and HLA Class II genes

BACKGROUND

The association with histocompatibility antigens (HLA), in particular Class II genes (DQB1, DRB1), has recently been suggested to be one of the genetic factors involved in testicular germ cell tumor (TGCT) development. The current study, which uses genotyping of microsatellite markers, was designed to replicate previous associations.

METHODS

In 151 patients, along with controls comprising parents or spouses, the HLA region (particularly Class II) on chromosome 6p21 was genotyped for a set of 15 closely linked microsatellite markers.

RESULTS

In both patients and controls, strong linkage disequilibrium was observed in the genotyped region, indicating that similar haplotypes are likely to be identical by descent. However, association analysis and the transmission disequilibrium test did not show significant results. Haplotype sharing statistics, a haplotype method that derives extra information from phase and single marker tests, did not show differences in haplotype sharing between patients and controls.

CONCLUSION

The current genotyping study did not confirm the previously reported association between HLA Class II genes and TGCT. As the HLA alleles for which associations were reported are also prevalent in the Dutch populations, these associations are likely to be nonexistent or much weaker than previously reported.

Molecular characterization of hiwi, a human member of the piwi gene family whose overexpression is correlated to seminomas

The piwi family genes are highly conserved during evolution and play essential roles in stem cell self-renewal, gametogenesis, and RNA interference in diverse organisms ranging from Drosophila melanogaster and C. elegans to Arabidopsis. Here we report the molecular characterization of hiwi, a human member of the piwi gene family. hiwi maps to the long arm of chromosome 12, band 12q24.33, a genomic region that displays genetic linkage to the development of testicular germ cell tumors of adolescents and adults (TGCTs), i.e., seminomas and nonseminomas. In addition, gain of this chromosomal region has been found in some TGCTs. hiwi encodes a 3.6 kb mRNA that is expressed abundantly in the adult testis. It encodes a highly basic 861-amino-acid protein that shares significant homology throughout its entire length with other members of the PIWI family proteins in Drosophila, C. elegans and mammals. In normal human testes, hiwi is specifically expressed in germline cells, with its expression detectable in spermatocytes and round spermatids during spermatogenesis. No expresssion was observed in testicular tumors of somatic origin, such as Sertoli cell and Leydig cell tumors. Enhanced expression was found in 12 out of 19 sampled testicular seminomas-tumors originating from embryonic germ cells with retention of germ cell phenotype. In contrast, no enhanced expression was detected in 10 nonseminomas-testicular tumors that originate from the same precursor cells as seminomas yet have lost their germ cell characteristics. Finally, no enhanced expression was detected in four spermatocytic seminomas-testicular tumors that most likely originate from germ cells capable of partial meiosis. Thus, hiwi is specifically expressed in both normal and malignant spermatogenic cells in a maturation stage-dependent pattern, in which it might function in germ cell proliferation.

Genome profiles of familial/bilateral and sporadic testicular germ cell tumors

In order to investigate the genetics of testicular germ cell tumors (TGCTs), we examined 33 TGCTs, including 15 familial/bilateral and 18 sporadic tumors, using comparative genomic hybridization. The frequencies of the histological subtypes were comparable between the two groups. Gains of the whole or parts of chromosome 12 were found in 30 tumors (91%). Furthermore, increased copy number of the whole or parts of chromosomes 7, 8, 17, and X, and decreased copy number of the whole or parts of chromosomes 4, 11, 13, and 18 were observed in > or = 50% of the tumors. Sixteen smallest regions of overlapping changes were delineated on 12 different chromosomes. The chromosomal copy numbers of familial/bilateral and sporadic TGCTs were comparable, suggesting similar genetic pathways to disease in both groups. However, significant differences were observed between the two main histological subgroups. Gains from 15q and 22q were associated with seminomas (P = 0.005 and P = 0.02, respectively), whereas gain of the proximal 17q (17q11.2-21) and high-level amplification from chromosome arm 12p, and losses from 10q were associated with nonseminomas (P < 0.001, P = 0.04, and P = 0.03, respectively).

Retinoic acid activates p53 in human embryonal carcinoma through retinoid receptor-dependent stimulation of p53 transactivation function

Although retinoids are known to regulate gene transcription by activating retinoid receptors, the targets of retinoid receptors are largely unknown. This study indicates effective all-trans retinoic acid (RA)-induced differentiation of human embryonal carcinoma cells engages p53. Unexpectedly, RA has been found to activate the transactivation function of p53 in the human embryonal carcinoma cell line, NT2/D1, in a retinoid receptor-dependent manner. A derived RA-resistant line, NT2/D1-R1, is deficient in this activity and is co-resistant to cisplatin. This indicates that RA and cisplatin responses may share a common pathway involving p53 in embryonal carcinomas. RA has no effect on p53 steady-state protein levels in either line. RA enhances endogenous p53 transactivation activity in NT2/D1 but not NT2/D1-R1 cells. In addition, RA induces transactivation activity of a gal4-p53 fusion protein, suggesting that RA activates p53 independent of increasing p53 levels or sequence-specific DNA binding. This activity is absent in retinoic acid receptor gamma (RARgamma)-deficient NT2/D1-R1 cells but can be restored upon co-transfection with specific RARs. Transient transfection of a dominant-negative p53 construct in NT2/D1 cells blocks the RA-mediated transcriptional decline of a differentiation-sensitive reporter plasmid and enhances survival of NT2/D1 cells following cisplatin treatment. Taken together, these findings indicate that RA activates the intrinsic activation function of p53 by a novel mechanism independent of effects on p53 stability or DNA binding and that this activation may be a general mechanism that contributes to RA-mediated G1 arrest.

Familial/bilateral and sporadic testicular germ cell tumors show frequent genetic changes at loci with suggestive linkage evidence

Testicular germ cell tumor (TGCT) is the most common tumor type among adolescent and young adult males. Familial clustering and bilateral disease are suggestive of a genetic predisposition among a subgroup of these patients, but susceptibility genes for testicular cancer have not yet been identified. However, suggestive linkage between disease and genetic markers has been reported at loci on chromosome arms 3q, 5q, 12q, 18q, and Xq. We have analyzed primary familial/bilateral (n=20) and sporadic (n=27) TGCTs, including 28 seminomas and 19 nonseminomas, for allelic imbalance (AI) within the autosomal regions. DNA from all tumors were analyzed by fluorescent polymerase chain reaction of 22 polymorphic loci at 3q27-ter, 5q13-35.1, 12q21-ter, and 18q12--ter. All tumor genotypes were evaluated against their corresponding constitutional genotypes. The percentages of TGCTs with genetic changes at 3q, 5q, 12q, and 18q, were 79%, 36%, 53% and 43%, respectively. The frequencies at 3q and 12q in nonseminomas were significantly higher than in seminomas (P=.003 and P=.004). In order to evaluate changes at hemizygous Xq loci, five loci were analyzed by co-amplification with an autosomal reference marker known to reveal retained heterozygosity in the tumor DNA. Gain of Xq sequences was seen in more than 50% of the tumors. The degree of amplification varied among the loci in each of five tumors, and based on these breakpoints, a common region of overlapping gains was found at Xq28. No significant differences were found between the frequencies of genetic changes in familial/bilateral versus sporadic tumors, an observation speaking in disfavor of the existence of a single susceptibility gene for TGCT in any of the analyzed regions. Our data suggest that gain of genetic material at distal Xq and losses at 5q and 18q contribute to establishment of seminomas, whereas imbalances at 3q as well as gain at distal part of 12q are associated with further progression into nonseminomas.

Cancer incidence in relatives of patients with testicular cancer in the eastern part of The Netherlands

OBJECTIVES

To investigate the incidence of malignant tumors in first-degree relatives of patients with testicular cancer.

METHODS

Information about the occurrence of cancer in relatives of patients treated for testicular germ cell cancer (TC) at the Department of Urology of the University Medical Centre Nijmegen from 1986 to 1997 was collected using postal questionnaires from 379 (72%) of 524 patients. The expected numbers of cancers in relatives were computed from age- and sex-specific incidence data in the Netherlands Cancer Registry. The observed/expected (O/E) ratios with 95% confidence intervals (CIs) were calculated using Byar's approximation of the exact Poisson test.

RESULTS

The O/E ratio for developing cancer in the families of patients with TC was 1.2 (95% CI 1.0 to 1.3). Among first-degree relatives of patients with TC, more TC was observed than expected (O/E 3.3; 95% CI 1.4 to 6.9). The risk for brothers of patients with TC increased 5.9-fold (95% CI 2.2 to 12.8). Both the risk of developing lung cancer (O/E 1.5) and malignancy of the female genital tract in sisters (O/E 2.8) was slightly increased. In contrast, the risk of urinary tract malignancies (O/E 0.3) and other and unknown primary tumors (O/E 0.2) had a lower incidence among relatives. However, both the increased and decreased risk of nontesticular cancer for first-degree relatives may have been caused by misclassification.

CONCLUSIONS

TC clusters in families were more pronounced among brothers than among fathers and sons. This study supports previous reports that families of patients with TC do not seem to be prone to nontesticular cancer. Additional investigations in families with TC are recommended to map candidate genes for TC.

A male germ cell tumor-susceptibility-determining locus, pgct1, identified on murine chromosome 13

Inbred 129 strain mice are predisposed to developing male germ cell tumors (GCTs) of the testes. The inherent genetic defects that underlie male GCT susceptibility in the 129 mouse strain are unknown. GCT incidence is increased in 129 strain males that lack functional p53 protein, and we have used this finding to facilitate the generation of panels of GCT-bearing intercross and backcross mice for genetic mapping analysis. A 129 strain locus, designated pgct1, that segregates with the male GCT phenotype has been identified on chromosome 13 near D13Mit188. This region of murine chromosome 13 may be syntenic to a portion of human chromosome 5q that is implicated in male GCT susceptibility in humans.

Localization to Xq27 of a susceptibility gene for testicular germ-cell tumours

Testicular germ-cell tumours (TGCT) affect 1 in 500 men and are the most common cancer in males aged 15-40 in Western European populations. The incidence of TGCT has risen dramatically over the last century. Known risk factors for TGCT include a history of undescended testis (UDT), testicular dysgenesis, infertility, previously diagnosed TGCT (ref. 7) and a family history of the disease. Brothers of men with TGCT have an 8-10-fold risk of developing TGCT (refs 8,9), whereas the relative risk to fathers and sons is fourfold (ref. 9). This familial relative risk is much higher than that for most other types of cancer. We have collected samples from 134 families with two or more cases of TGCT, 87 of which are affected sibpairs. A genome-wide linkage search yielded a heterogeneity lod (hlod) score of 2.01 on chromosome Xq27 using all families compatible with X inheritance. We obtained a hlod score of 4.7 from families with at least one bilateral case, corresponding to a genome-wide significance level of P=0.034. The proportion of families with UDT linked to this locus was 73% compared with 26% of families without UDT (P=0.03). Our results provide evidence for a TGCT susceptibility gene on chromosome Xq27 that may also predispose to UDT.

Geographic clustering of testicular cancer incidence in the northern part of The Netherlands

Geographic variations in testicular cancer incidence may be caused by differences in environmental factors, genetic factors, or both. In the present study, geographic patterns of age-adjusted testicular cancer incidence rates (IRs) in 12 provinces in The Netherlands in the period 1989-1995 were analysed. In addition, the age-adjusted IR of testicular cancer by degree of urbanization was evaluated. Cancer incidence data were obtained from the Netherlands Cancer Registry. The overall annual age-adjusted IR of testicular cancer in The Netherlands in the period 1989-1995 was 4.4 per 100000 men. The province Groningen in the north of the country showed the highest annual IR with 5.8 per 100000 men, which was higher (P < 0.05) than the overall IR in The Netherlands (incidence rate ratio (IRR) 1.3, 95% confidence interval (CI) 1.1-1.6). The highest IR in Groningen was seen for both seminomas and non-seminomas. In addition, Groningen showed the highest age-specific IRs in all relevant younger age groups (15-29, 30-44 and 45-59 years), illustrating the consistency of data. The province Friesland, also situated in the northern part of the country, showed the second highest IR of testicular cancer with 5.3 cases per 100000 men per year (IRR 1.2, 95% CI 1.0-1.5, not significant). This mainly resulted from the high IR of seminoma in Friesland. Analysis of age-adjusted IRs of testicular cancer by degree of urbanization in The Netherlands showed no urban-rural differences at analysis of all histological types combined, or at separate analyses of seminomas and non-seminomas. Geographic clustering of testicular cancer seems to be present in the rural north of The Netherlands with some stable founder populations, which are likely to share a relatively high frequency of genes from common ancestors including genes possibly related to testicular cancer. Although this finding does not exclude the involvement of shared environmental factors in the aetiology of testicular cancer, it may also lend support to a genetic susceptibility to testicular cancer development. Testicular cancer cases in stable founder populations seem particularly suitable for searching for testicular cancer susceptibility genes because such genes are likely to be more frequent among affected men in such populations.

Familial testicular cancer in a single-centre population

Familial occurrence of testicular cancer suggests a genetic predisposition to the disease. A genetic susceptibility may also be reflected by the occurrence of bilateral testicular neoplasms and the high rates of urogenital developmental anomalies in families prone to testicular cancer. In this study, the proportion of familial testicular cancer cases was analyzed retrospectively in a single-centre population of 693 testicular cancer patients treated between 1977 and 1997 and the relative risk (RR) for first-degree relatives of patients was estimated. In addition, the existence of bilateral testicular neoplasms and urogenital developmental anomalies in familial testicular cancer patients was evaluated. 24 of the 693 patients (3.5%) had a first-degree relative with testicular cancer. These 24 cases belonged to 17 families; in 7 of these 17 families both affected first-degree family members were part of the study population of 693 patients. Consequently, the 693 studied patients belonged to a total of 686 families. Thus, the actual proportion of familial testicular cancer was 2.5% (17 of 686 families). The familial cases consisted of 11 brother pairs, including 2 pairs of identical twins and 1 pair which also had two affected cousins, and 6 father-son pairs (in total 36 cases, 12 treated elsewhere). Estimates of the RR to first-degree relatives showed a 9- to 13-fold increased RR to brothers (P < 0.001) and a 2-fold increased RR to fathers (P = non-significant (n.s)) of testicular cancer patients. Among the 36 patients with familial testicular cancer, 2 (5.6%) had bilateral testicular cancer, 4 (11.1%) had undescended testis, 3 (8.3%) had inguinal hernia, and 1 (2.8%) showed renal hypoplasia. The present data on familial occurrence of testicular cancer may lend support to a role of genetic factors in the aetiology of testicular cancer.

Chromosomal deletions occur in restricted regions of 5q in testicular germ cell cancer

Since the biologic behavior and molecular genetic changes observed in testicular germ cell cancer differ from those seen in more common epithelial tumors, it is likely that hitherto uncharacterized genes play a role in the development of germ cell tumors. Our previous work on testicular germ cell cancer suggested that chromosome 5q might contain one or more novel tumor suppressor genes that play a role in this malignancy. In this study, we performed a high resolution loss of heterozygosity (LOH) study of testicular cancer using 37 informative markers on chromosome 5. We detected allelic losses in 20/48 (42%) specimens and identified three common sites of loss on chromosome 5q14, 5q21 and 5q34-qter, defined respectively by minimal regions of deletion of < or = 1 cM, 10 cM and approximately 20 (cM). Using an overlapping series of YACs and radiation hybrid mapping, we have constructed a physical map of the 5q14 deletion that should aid in the isolation and characterization of the putative tumor suppressor gene located therein.

Germ cell cancer

The publication of the proceedings of Fourth Workshop on Carcinoma in situ was an impressive leap in our understanding of the interaction between prenatal and postpubertal factors in the development of germ cell cancer as well as increased insight into the molecular events that are involved in the development of these tumors. From this work, physicians are increasingly accepting that estrogen-mediated prenatal priming of germ cells generates a predisposition to postpubertal cyclin D2-driven initiation of full mitotic cell cycle replication of a tetraploid p53-expressing meiotically arrested pachytene spermatocyte that is under increased gonadotrophin drive because of testicular atrophy inducing events. From this new knowledge, new markers, eg, FGF4, CD30, and OCT-4, of embryonal carcinoma cells are identifying alternative ways of identifying poor risk tumors and leading to renewed interest in study of histopathology of these tumors. With greater attention to late events and increasing confirmation that chemotherapy is better than radiation even in seminoma and that seminoma is more chemosensitive than nonseminoma, a renewed clinical need exists for improved pathologic definition to reduce unnecessary usage of chemotherapy and maximize its benefits. With the failure of vinblastine, ifosfamide, and cisplatin to show any benefit over BEP (bleomycin, etoposide, and cisplatin) in the Southwest Oncology Group trial, re-examination of approaches to treatment of poor risk disease is emphasized as the priority for future trials.

Testicular germ cell tumors: molecular understanding and clinical implications

It was recognized in the 1960s that testicular germ cell tumors were curable with chemotherapeutic drugs. Since that time, newer drugs including cisplatin have increased the cure rate of these tumors to over 80%, even in patients with metastatic disease. Germ cell tumors also exhibit a unique biology and genetics that distinguish them from other solid tumors and might contribute to their routine curability.