Mediastinal germ cell tumors: many questions and perhaps an answer

Pathogenesis and pathobiology of testicular germ cell tumours: a view from a developmental biological perspective with guidelines for pathological diagnostics

Testicular germ cell tumours (GCT) are divided into three different subtypes (types I-III) regarding to their developmental origin, histological differences and molecular features. Type I GCT develop from disturbed primordial germ cells and most commonly occur in children and young adolescents, which is why they are referred to as prepubertal GCT. Type II GCT develop from a non-invasive germ cell neoplasia in situ (GCNIS) and show an isochromosome 12p (i12p) or gain of 12p material as a common and characteristic molecular alteration. Type III GCT originate from distorted postpubertal germ cells (e.g. spermatogonia) in adult patients and have changes on chromosome 9 with amplification of the DMRT1 gene. Type I GCT encompass prepubertal-type teratomas and yolk-sac tumours (YST). Type II GCT include seminoma, embryonal carcinoma, choriocarcinoma, postpubertal-type teratoma and postpubertal-type YST. Types I and II GCT both show similar morphology, but are separated from each other by the detection of a GCNIS and an i12p in type II GCT. For type II GCT it is especially important to detect non-seminomatous elements, as these tumours have a worse biological behaviour and need a different treatment to seminomas. In contrast to types I and II GCT, type III tumours are equivalent to spermatocytic tumours and usually occur in elderly men, with few exceptions in young adults. The development of types I and II GCT seems to depend not upon driver mutations, but rather on changes in the epigenetic landscape. Furthermore, different pluripotency associated factors (e.g. OCT3/4, SOX2, SOX17) play a crucial role in GCT development and can be used as immunohistochemical markers allowing to distinguish the different subtypes from each other in morphologically challenging tissue specimens. Especially in metastatic sites, a morphological and immunohistochemical diagnostic algorithm is important to detect small subpopulations of each non-seminomatous GCT subtype, which are associated with a poorer prognosis and need a different treatment. Furthermore, primary extragonadal GCT of the retroperitoneum or mediastinum develop from misguided germ cells during embryonic development, and might be challenging to detect in small tissue biopsies due to their rarity at corresponding sites. This review article summarises the pathobiological and developmental aspects of the three different types of testicular GCT that can be helpful in the histopathological examination of tumour specimens by pathologists.

Primary germ cell tumours of the mediastinum: A review with emphasis on diagnostic challenges

This article will review current aspects of the histopathological, immunohistochemical and molecular analysis of primary mediastinal germ cell tumours (PMGCTs) as well as their aetiological, epidemiological, clinical and therapeutic features. PMGCTs represent an important differential diagnosis in the spectrum of mediastinal tumours, and their diagnosis is usually made on small tissue samples from core needle biopsies in combination with diagnostic imaging and serum tumour markers. As in lymphomas, a small biopsy is often the only viable tumour sample available from these patients, as they receive chemotherapy prior to eventual surgical resection. Pathologists therefore need to apply an efficient combination of immunohistochemical markers to confirm the diagnosis of a PMGCT and to exclude morphological mimics.

Novel application of Roux-en-Y for diversion of a cutaneous fistula from an irresectable mesenteric root mature teratoma: a case report

Reconfiguration of the alimentary tract with the Roux-en-Y has been utilized in a wide variety of contexts since its first description by Swiss physician César Roux. We present a novel and unique application of the Roux-en-Y whereby a chronically discharging cutaneous fistula originating at a retroperitoneal mature teratoma within the root of the mesentery was diverted enterically via a cystojejunostomy and the fistula tract excised, providing a resolution of symptoms. The location of the tumour in the root of the mesentery and the involvement of major mesenteric vessels made a radical resection of the tumour technically impossible but due to the distressing symptoms caused by the fistula made diversion of the fistula an excellent treatment option.

Analysis of prognostic factors and establishment of prognostic model for primary mediastinal germ cell tumors: a case controlled study

BACKGROUND

The overall prognosis of primary mediastinal germ cell tumors (PMGCTs) is poor and the associated prognostic factors are not fully understood. Our goal was to investigate the prognostic factors of PMGCTs and to develop a validated prognostic prediction model.

MATERIALS AND METHODS

A total of 114 PMGCTs with specific pathological types were included in this study. Clinicopathological characteristics of nonseminomatous PMGCTs and mediastinal seminomas were compared using the χ2 or Fisher's exact test. Independent prognostic factors of nonseminomatous PMGCTs screened using the univariate and multivariate Cox regression analysis were then used to generate a nomogram. The predictive performance of the nomogram was evaluated using the concordance index, decision curve, and the area under the receiver operating characteristic curve (AUC) and validated by bootstrap resampling. The Kaplan-Meier curves of independent prognostic factors were analyzed.

RESULTS

This study included 71 cases of nonseminomatous PMGCTs and 43 cases of mediastinal seminomas. The 3-year overall survival rates for nonseminomatous PMGCTs and mediastinal seminomas patients were 54.5 and 97.4%, respectively. The overall survival prognostic nomogram for nonseminomatous PMGCTs was established by integrating independent prognostic factors, including the Moran-Suster stage, white blood cell, hemoglobin, and platelet-lymphocyte ratio. The nomogram demonstrated good performance with a concordance index of 0.760 and the 1-year and 3-year AUC values of 0.821 and 0.833, respectively. These values were better than those of the Moran-Suster stage system. The bootstrap validation had an AUC of 0.820 (0.724-0.915) and showed a well-fitting calibration curve. Besides, patients with mediastinal seminomas showed favorable clinical outcomes and all the nine patients received neoadjuvant therapy and postoperative surgery achieved pathological complete response.

CONCLUSION

A nomogram based on staging and blood routine examination results was established to accurately and consistently predict the prognosis of patients with nonseminomatous PMGCTs.

Testicular germ cell tumors: Genomic alternations and RAS-dependent signaling

Testicular germ cell tumors (TGCTs) are a common malignancy occurring in young adult men. The various genetic risk factors have been suggested to contribute to TGCT pathogenesis, however, they have a distinct mutational profile with a low rate of somatic point mutations, more frequent chromosomal gains, and aneuploidy. The most frequently mutated oncogenes in human cancers are RAS oncogenes, while their impact on testicular carcinogenesis and refractory disease is still poorly understood. In this mini-review, we summarize current knowledge on genetic alternations of RAS signaling-associated genes (the single nucleotide polymorphisms and point mutations) in this particular cancer type and highlight their link to chemotherapy resistance mechanisms. We also mention the impact of epigenetic changes on TGCT progression. Lastly, we propose a model for RAS-dependent signaling networks, regulation, cross-talks, and outcomes in TGCTs.

Age-incidence patterns of seminoma and nonseminoma among males and females in Germany and the United States, 2008-2016

BACKGROUND & OBJECTIVES

The comparison of the incidence of gonadal germ cell tumors among males and females can provide insights that cannot be gained by separately studying these tumors.

MATERIAL AND METHODS

Incidence data on male and female gonadal germ cell tumors were drawn from the cancer registries of North Rhine-Westphalia, Germany, and the United States Surveillance, Epidemiology and End Results program, for non-Hispanic White persons only, for the years 2008-2016. We estimated age-standardized and age-, and histology-specific incidence rates.

RESULTS

We included 21,840 male and 716 female gonadal germ cell tumors. Incidence rates among males were higher in Germany (95.8 per million, standard error [SE] 1.1) than in the United States (68.0, SE 0.6), while incidence rates among females were lower in Germany (1.9, SE 0.2) than in the United States (2.6, SE 0.1). The characteristic peak of infantile (age 0-4 years) germ cell tumors among males were missing among females. The age peak of ovarian germ cell tumors occurred 15-20 years earlier (Germany: 10-14 years, United States: 15-19 years) than the age peak of testicular germ cell tumors (30-34 years). The three most common testicular germ cell tumors histologies were seminoma, mixed germ cell tumors, and embryonal carcinoma Among females, the three most common ovarian germ cell tumors histologies were teratoma, yolk sac tumor, monodermal teratomas, and somatic-type tumors arising from dermoid cysts in both countries.

DISCUSSION

The characteristic peak of infantile (age 0-4 years) germ cell tumors among males was missing among females. The shapes of the age-specific incidence curves are similar for males and females in Germany and the United States, though with much lower incidence rates in females, suggesting a common pathogenesis.

CONCLUSION

The lower rates among females may be due to the lower number of initiated tumors in the absence of the Y-chromosome, and the earlier peak among females may be due to a younger age at puberty.

The Role of TP53 in Cisplatin Resistance in Mediastinal and Testicular Germ Cell Tumors

Germ cell tumors (GCTs) are considered to be highly curable; however, there are major differences in the outcomes related to histology and anatomical localization. GCTs originating from the testis are, overall, sensitive to platinum-based chemotherapy, whereas GCTs originating from the mediastinum show a worse response, which remains largely unexplained. Here, we address the differences among GCTs from two different anatomical locations (testicular versus mediastinal/extragonadal), with a specific focus on the role of the P53 pathway. It was recently shown that GCTs with TP53 mutations most often localize to the mediastinum. To elucidate the underlying mechanism, TP53 knock-out lines were generated in cisplatin-sensitive and -resistant clones of the representative 2102Ep cell line (wild-type TP53 testicular GCT) and NCCIT cell line (hemizygously mutated TP53, mutant TP53 mediastinal GCT). The full knock-out of TP53 in 2102Ep and resistant NCCIT resulted in an increase in cisplatin resistance, suggesting a contributing role for P53, even in NCCIT, in which P53 had been reported to be non-functional. In conclusion, these results suggest that TP53 mutations contribute to the cisplatin-resistant phenotype of mediastinal GCTs and, therefore, are a potential candidate for targeted treatment. This knowledge provides a novel model system to elucidate the underlying mechanism of clinical behavior and possible alternative treatment of the TP53 mutant and mediastinal GCTs.

Primary Mediastinal and Testicular Germ Cell Tumors in Adolescents and Adults: A Comparison of Genomic Alterations and Clinical Implications

Simple Summary

The germ cell tumors (GCTs) family is a heterogeneous group of neoplasms that includes tumors affecting testis (TGCTs) and rarer cases occurring in extragonadal sites. Mediastinal germ cell tumors (MGCTs) are more aggressive and have poorer prognosis. Due to their rarity of MGCTs, few molecular and clinical studies are reported. MGCTs share biological similarities with TGCT, and international guidelines recommend use of the same therapies validated for TGCT. However, while high response rate is achieved in TGCT, MGCT tend to be resistant to therapy. This review resumes all molecular findings reported in MGCTs, summarizing molecular characteristics common with TGCT and highlighting the different molecular alterations that characterize mediastinal tumors. A deeper understanding of the MGCT biology will help in clinical management of these patients.

Abstract

Mediastinal germ cell tumors (MGCTs) share histologic, molecular and biomarkers features with testicular GCTs; however, nonseminomatous MGCTs are usually more aggressive and have poorer prognosis than nonseminomatous TGCTs. Most nonseminomatous MGCT cases show early resistance to platinum-based therapies and seldom have been associated with the onset of one or more concomitant somatic malignancies, in particular myeloid neoplasms with recent findings supporting a common, shared genetic precursor with the primary MGCT. Genomic, transcriptomic and epigenetic features of testicular GCTs have been extensively studied, allowing for the understanding of GCT development and transformation of seminomatous and nonseminomatous histologies. However, MGCTs are still lacking proper multi-omics analysis and only few data are reported in the literature. Understanding of the mechanism involved in the development, in the progression and in their higher resistance to common therapies is still poorly understood. With this review, we aim to collect all molecular findings reported in this rare disease, resuming the similarities and disparities with the gonadal counterparts.

Primary mediastinal germ cell tumours: an immunohistochemical and molecular diagnostic approach

AIMS

Primary mediastinal germ cell tumours (PMGCTs) are rare mediastinal neoplasms and their diagnosis can be challenging due to small biopsy samples. The aim of this study was to elaborate a diagnostic algorithm using immunohistochemical stainings with focus on novel markers and molecular analysis of isochromosome 12p [i(12p)].

METHODS AND RESULTS

Paraffin-embedded tissues of 32 mediastinal tumours were analysed using immunohistochemical stainings for SALL4, LIN28, OCT3/4, D2-40, CD117, SOX17, SOX2, CD30, ß-hCG, GATA3, FOXA2, GPC3, AFP, TdT, NUT and pan-cytokeratin. Quantitative real-time polymerase chain reaction (qPCR) was performed to investigate i(12p) status. Fifteen seminomas, seven teratomas, one yolk sac tumour, one choriocarcinoma and seven mixed PMGCT were diagnosed. Each entity had different immunohistochemical staining patterns which helped to distinguish them: seminoma (OCT3/4, D2-40, CD117, TdT), embryonal carcinoma (OCT3/4, SOX2), yolk sac tumour (FOXA2, GPC3, AFP) and choriocarcinoma (ß-hCG, GATA3). Mature teratomas stained positive for pan-cytokeratin in epithelial components and focally for SALL4, SOX2, GATA3, D2-40 and FOXA2. Furthermore, a NUT carcinoma mimicking a PMGCT was diagnosed showing a strong nuclear SOX2 and speckled nuclear NUT staining. i(12p) was detected in 24 out of 27 PMGCTs [89%].

CONCLUSION

A diagnostic algorithm is of great importance for a reliable diagnosis of PMGCTs in the usually small tissue biopsy samples. Therefore, a combination of three to four antibodies to identify the correct histological subtype is usually necessary in addition to morphological features. The i(12p) status serves as an additional option to underline germ cell origin in selected cases.

Treatment and Survival of Malignant Extracranial Germ Cell Tumours in the Paediatric Population: A Systematic Review and Meta-Analysis

OBJECTIVE

This systematic review and meta-analysis was performed to explore overall survival (OS) and event free survival (EFS) rates internationally over the past two decades and to define specific subgroups with inferior outcomes which may demand different treatment strategies.

METHODS

The search focused on malignant extracranial germ cell tumours (GCTs) in the paediatric population. The initial database search identified 12,556 articles; 32 articles were finally included in this review, comprising a total of 5095 patients.

RESULTS

The studies were heterogeneous, varying from single institution reports to large prospective trials. Older studies, describing eras where non-platinum-based chemotherapy regimens were used, showed clearly worse outcomes. Survival for stage I-II gonadal disease is excellent. On the other hand, patients with an initial alpha-fetoprotein (AFP) > 10,000 ng/mL or kU/L, age > 11 years and stage IV disease confer a survival disadvantage. For testicular disease in particular, lymphovascular invasion and certain histopathological subtypes, such as embryonal carcinoma (EC) and mixed malignant GCTs, survival is poorer. Survival data for sacrococcygeal and mediastinal GCTs show a heterogeneous distribution across studies in this review, independent of year of publication. Patients > 12 years presenting with a mediastinal GCT pose a subpopulation which fares worse than GCTs in other locations or age groups. This is independent of AFP levels, stage of disease or treatment protocol, and these patients may demand a different treatment strategy.

CONCLUSIONS

This review describes the heterogeneous nature of GCTs in different anatomical locations, impacting on stage at presentation, treatment modalities used and survival data. Despite this heterogeneity, in line with the current developmental biology-based classification system, subpopulations can be defined which have an inferior EFS and OS and where future research and more individualised treatment would help to improve survival.