“Somatic-type” Malignancies Arising From Testicular Germ Cell Tumors: A Clinicopathologic Study of 124 Cases With Emphasis on Glandular Tumors Supporting Frequent Yolk Sac Tumor Origin

Primitive Embryonic-Type Neuroectodermal/Glandular Complexes in Testicular Germ Cell Tumors: A Mimic of Embryonic-Type Neuroectodermal Tumor

Embryonic-type neuroectodermal elements are often intimately mixed with primitive endodermal-type glands, like those of yolk sac tumors, in germ cell neoplasia in situ (GCNIS)-derived germ cell tumors of the testis. Because the primitive glands mimic tubules or rosettes of embryonic-type neuroectodermal elements, these embryonic-type neuroectodermal/glandular complexes may be misinterpreted as pure lesions of embryonic-type neuroectodermal elements, which, if of sufficient size, may lead to a diagnosis of embryonic-type neuroectodermal tumor, despite that the criteria of the World Health Organization for a "somatic-type malignancy" are not met. A diagnosis of embryonic-type neuroectodermal tumor in the testis may lead to retroperitoneal lymphadenectomy even in clinical stage I patients, and in postchemotherapy resections indicates a poor prognosis. The distinction of the neuroectodermal and glandular elements is not always straightforward based on morphology alone. We, therefore, studied 34 testis-derived germ cell tumors with embryonic-type neuroectodermal/glandular complexes and 2 purely glandular yolk sac tumors to characterize the immunophenotypes and determine an efficient immunohistochemical panel to aid in this differential. We found that GFAP, synaptophysin, and paired-like homeobox 2B (PHOX2B) expression was specific to embryonic-type neuroectodermal elements, although PHOX2B had poor sensitivity. In contrast, positive reactions with antibodies directed against AFP, villin, and CDX2 were specific for the glandular elements, although CDX2 had poor sensitivity. Other markers, including AE1/AE3 cytokeratin, SALL4, glypican 3, SOX2, SOX11, CD56, INSM1, and neurofilament, proved less helpful because of their nonspecificity and/or poor sensitivity. We conclude that the optimal immunohistochemical panel for distinguishing the components of embryonic-type neuroectodermal/glandular complexes includes stains for synaptophysin, GFAP, villin, and AFP.

Beta-Catenin Alterations in Postchemotherapy Yolk Sac Tumor, Postpubertal-Type With Enteroblastic Features

Postchemotherapy postpubertal-type yolk sac tumors (YST) with glandular and solid phenotypes are aggressive and commonly resistant to systemic chemotherapy. These neoplasms show morphologic features that significantly overlap with those of somatic carcinomas with "enteroblastic" or "fetal" phenotype (the preferred terminology depends on the site of origin). They often present as late or very late recurrences, and their diagnosis is challenging because they frequently affect patients in an age group at risk for carcinomas of somatic origin. Recently, we incidentally identified examples of postchemotherapy glandular and solid YST with "enteroblastic" phenotypes and nuclear expression of beta-catenin, prompting us to further evaluate the prevalence of this phenomenon. We found nuclear expression of beta-catenin in 10 (29%) of 34 such tumors. A subset of cases with nuclear beta-catenin expression was further analyzed with a DNA sequencing panel (n = 6) and fluorescence in situ hybridization for isochromosome 12p [i(12p); n = 5]. Sequencing identified exon 3 CTNNB1 variants in 3 (50%) of 6 analyzed cases, and fluorescence in situ hybridization was positive for i(12p) in 5 of 5 cases. In conclusion, a significant subset of postchemotherapy YST with glandular or solid architecture and "enteroblastic" phenotype demonstrates beta-catenin alterations, suggesting that activation of Wnt signaling may play a role in the progression of these neoplasms. Moreover, nuclear beta-catenin expression in these tumors represents a potential diagnostic pitfall given that carcinomas of true somatic origin with overlapping morphology may also be positive for this marker.

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.

Analysis of GATA3 and FOXA2 expression suggests that downregulation of genes involved in the maintenance of a mature yolk sac tumor phenotype may underlie sarcomatoid transformation

In the post-chemotherapy setting, germ cell tumors of the testis (GCTT) that resemble non-specific sarcomas and co-express cytokeratins and glypican-3 (GPC3) are diagnosed as "sarcomatoid yolk sac tumor postpubertal-type (YSTpt)". The diagnosis of sarcomatoid YSTpt is clinically relevant but challenging due to its rarity, non-specific histology, and negative α-fetoprotein (AFP) staining. Recently, FOXA2 has emerged as a key-gene in the reprogramming of GCTT (activating the transcription of several genes, among which GATA3), and immunohistochemical studies showed that GATA3 and FOXA2 have a higher sensitivity for non-sarcomatoid YSTpt than GPC3 and AFP. We found that sarcomatoid YSTpt did not express FOXA2 [0: 14/14 (100%)] and showed focal expression of GATA3 [0: 12/14 (85.7%), 1 + : 2/14 (14.3%)], thus suggesting that these markers are not useful in diagnosing this tumor. Furthermore, we proposed a potential mechanism of sarcomatoid transformation in the post-chemotherapy setting of GCTT, mediated by the downregulation of FOXA2 and GATA3.

Retroperitoneal Sarcomatoid Yolk Sac Tumor in a Chemotherapy-Naive Patient With Testicular Postpubertal Type Teratoma: A Rare Case Report With Emphasis on Molecular Features

Sarcomatoid yolk sac tumor is a very rare histologic type of testicular germ cell tumor and is mainly reported in testicular germ cell tumor patients who receive chemotherapy. Herein, we report an extremely rare concurrent retroperitoneal sarcomatoid yolk sac tumor in a man with a testicular postpuberal teratoma before he received chemotherapy. A 37-year-old man initially presented with a persistent abdominal pain. Subsequent imaging studies revealed a 9.6-cm retroperitoneal mass, and 2 testicular masses (3.1 cm and 0.9 cm in greatest dimension, respectively). His serum tumor markers were within normal ranges. His radical orchiectomy demonstrated a postpubertal type teratoma with an adjacent scarring nodule. Later, his retroperitoneal tumor showed spindle tumor cells embedded in predominantly myxoid and focally fibrous stroma with diffuse and strong immunoreactivity for keratin AE1/AE3, SALL4 and glypican 3. No tumor necrosis or brisk mitotic figures were observed. A diagnosis of sarcomatoid yolk sac tumor was rendered. Fluorescence in situ hybridization analysis of his retroperitoneal sarcomatoid yolk sac tumor revealed polysomy 12 and MYC amplification, whereas no evidence of isochromosome 12p [i(12p)], and DNA sequencing showed 6 mutations per megabase (muts/Mb), and the somatic alterations included ARAF amplification and ATR I774Yfs*5. Considering its rarity, sarcomatoid yolk sac tumor may pose diagnostic challenges. Therefore, relevant clinicoradiologic information and ancillary work up, including immunohistochemistry and molecular studies, may be helpful for the accurate classification. Our tumor further raises awareness of this rare event, expands the spectrum of its clinical presentation, and explores the molecular features.

SMARCB1-Deficient Skull Base Chondrosarcoma with 12p Duplication Presenting as Somatic-Type Malignancy Arising from Metastatic Seminoma

Somatic-type malignancy (STM) can occur infrequently within a primary or metastatic testicular germ cell tumor (TGCT) and is associated with dismal prognosis and survival. STM with chondrosarcomatous features is exceedingly rare and head and neck involvement has not been previously documented. A 39-year-old white man presented with nasal obstruction and epistaxis. Imaging disclosed a 6.9-cm expansile tumor involving the nasal cavity and skull base with intraorbital and intracranial extension. The histopathologic properties of the tumor were compatible with chondrosarcoma, grade II-III. Immunohistochemically, malignant cells were strongly and diffusely positive for S100 and epithelial markers, and showed loss of SMARCB1 expression. IDH1/2 mutations were not detected. Following whole-body PET scan, a 7.0-cm left testicular mass was discovered and diagnosed as seminoma with syncytiotrophoblastic cells, stage pT3NXM1b. Extensive retroperitoneal, mediastinal, and supraclavicular lymphadenopathy was also noticed. Histopathologic examination of the left supraclavicular lymph node revealed metastatic seminoma. By FISH, most metastatic nodal seminoma cells harbored 1 to 4 copies of isochromosome 12p, while the chondrosarcoma featured duplication of 12p. Presence of a malignant TGCT with disseminated supradiaphragmatic lymphadenopathy, the unique immunophenotypic properties of the skull-based chondrosarcoma and lack of IDH1/2 aberrations with gain of 12p strongly support the diagnosis of STM chondrosarcoma arising from metastatic TGCT. The patient did not respond to chemotherapy and succumbed three months after diagnosis. Although exceedingly uncommon, metastasis to the head and neck may occur in patients with TGCT. This case of STM chondrosarcoma demonstrated divergent immunophenotypic and molecular characteristics compared to "typical" examples of head and neck chondrosarcoma. High index of suspicion is advised regarding the diagnosis of lesions that present with otherwise typical histomorphology but unexpected immunohistochemical or molecular features.

Characterizing the mutational burden, DNA methylation landscape, and proteome of germ cell tumor-related somatic-type malignancies to identify the tissue-of-origin, mechanisms of therapy resistance, and druggable targets

BACKGROUND

Germ cell tumors (GCT) might undergo transformation into a somatic-type malignancy (STM), resulting in a cell fate switch to tumors usually found in somatic tissues, such as rhabdomyosarcomas or adenocarcinomas. STM is associated with a poor prognosis, but the molecular and epigenetic mechanisms triggering STM are still enigmatic, the tissue-of-origin is under debate and biomarkers are lacking.

METHODS

To address these questions, we characterized a unique cohort of STM tissues on mutational, epigenetic and protein level using modern and high-throughput methods like TSO assays, 850k DNA methylation arrays and mass spectrometry.

RESULTS AND CONCLUSIONS

For the first time, we show that based on DNA methylation and proteome data carcinoma-related STM more closely resemble yolk-sac tumors, while sarcoma-related STM resemble teratoma. STM harbor mutations in FGF signaling factors (FGF6/23, FGFR1/4) highlighting the corresponding pathway as a therapeutic target. Furthermore, STM utilize signaling pathways, like AKT, FGF, MAPK, and WNT to mediate molecular functions coping with oxidative stress, toxin transport, DNA helicase activity, apoptosis and the cell cycle. Collectively, these data might explain the high therapy resistance of STM. Finally, we identified putative novel biomarkers secreted by STM, like EFEMP1, MIF, and DNA methylation at specific CpG dinucleotides.

Reprint of: somatic-type malignancies in testicular germ cell tumors

The development of somatic-type malignancy (SM) in testicular germ cell tumor represents a major challenge in the diagnosis and treatment of testicular cancer. Most SMs are derived from teratoma, and the remainder is associated with yolk sac tumor. They occur more frequently in metastases than in primary testicular tumors. SMs demonstrate a variety of histologic types, including sarcoma, carcinoma, embryonic-type neuroectodermal tumor, nephroblastoma-like tumor, and hematologic malignancy. Sarcoma, particularly rhabdomyosarcoma, accounts for the majority of SMs in the primary testicular tumors, whereas carcinoma, particularly adenocarcinoma, is the most common SM in metastases. Although SMs derived from testicular germ cell tumors mimic their histologic counterparts in other organs with overlapping immunohistochemical profiles, isochromosome 12p is present in most SMs, which can be useful in the differential diagnosis. The presence of SM in the primary testicular tumor may not worsen the outcome, but the development of SM in metastasis is associated with a poor prognosis. Furthermore, somatic-type carcinoma is likely associated with a worse prognosis than somatic-type sarcoma. Although SMs respond poorly to the cisplatin-based chemotherapy, timely surgical resection is an effective treatment for most patients.

An update on diagnostic tissue-based biomarkers in testicular tumors

Testicular cancer is rare overall but comprises the most common solid malignancy diagnosed in young men aged ∼20-40 years. Most testicular neoplasms generally fall into 2 broad categories: germ cell tumors (GCTs; ∼95%) and sex cord-stromal tumors (SCSTs ∼5%). Given the relative rarity of these tumors, diagnostic biomarkers are highly relevant for their diagnosis. Over the past several decades, diagnostic biomarkers have improved dramatically through targeted immunohistochemical and molecular characterization. Despite these recent advances, most markers are not perfectly sensitive or entirely specific. Therefore, they need to be used in combination and interpreted in context. In this review, we summarize tissue-based biomarkers relevant to the pathologist, with a focus on practical diagnostic issues that relate to testicular GCT and SCST.

Unresectable Metastatic Testicular Germ Cell Tumor With Low-grade Neuroglial Neoplasm, Stable After Radiation and Chemotherapy

We present an 18-year-old male patient who presented with a 16 cm testicular tumor alongside multiple lesions in the lungs, right pelvis with involvement of the ischio/pubic bone, and enlarged pelvic lymph nodes on imaging, suspicious for metastatic disease. Histologic and immunohistochemical examinations revealed an embryonic type neuroectodermal tumor (somatic-type malignancy, 10%) arising in a malignant mixed germ cell tumor composed of teratoma (50%), embryonal carcinoma (10%) and yolk sac tumor (30%). After treatment with chemotherapy and radiation, repeat imaging demonstrated a right pelvic sidewall mass that decreased in size from 40 mm at 11 months after the initial diagnosis to 18 mm at 22 months after the initial diagnosis. A right pelvis medial thigh wall mass that had a lytic bone component showed a slight increase in size from 151 mm at 11 months after the initial diagnosis to 154 mm at 22 months after the diagnosis. On biopsies performed at 3, 10, and 26 months after the initial diagnosis, this lytic lesion consistently demonstrated a neoplasm composed of low-grade neuroglial differentiation. This is the first case in the medical literature where a residual malignant germ cell tumor consisting of low-grade neuroglial neoplasm is in a site that is not amenable to resection without significant morbidity. The tumor initially regressed with the traditional first-line chemo-radiotherapy regimen but regrew and stabilized with a second regimen of chemotherapy. The clinical course of this case invites consideration for an active surveillance approach in cases with similar characteristics.

Germ cell neoplasms of the testis: Update for 2022

Germ cell neoplasia in situ (GCNIS) is the precursor of both seminomatous and non-seminomatous germ cell tumors. It consists of distended tubules that may have either intratubular seminoma or intratubular embryonal carcinoma cells. Many invasive non-seminomatous tumors contain a mixture of tumor types, which are reviewed here. Morphology, aided by a panel of immunostains, can determine the presence and percent of embryonal carcinoma, yolk sac tumor, choriocarcinoma, or teratoma in such tumors. Use of immunostains, required for diagnosis in perhaps 25% of testicular neoplasms, is reviewed. Changes of classification in the AJCC (8^th edition) in 2016 are discussed, including the partitioning of two tumor types: the central role of chromosome 12p amplification allows both teratoma and yolk sac tumor to be divided into prepubertal types (lacking amplification) and post-pubertal types. Occasionally, sex cord-stromal tumors, hematolymphoid tumors, or epididymal adenomatoid tumors enter the differential diagnosis of germ cell neoplasms.

Molecular correlates of male germ cell tumors with overgrowth of components resembling somatic malignancies

A small subset of male germ cell tumors (GCT) demonstrates overgrowth of histologic components that resemble somatic malignancies (e.g., sarcoma, carcinoma). The presence of so-called "somatic-type" malignancies (SM) in GCT has been associated with chemotherapy-resistance and poor clinical outcomes in prior studies. However, the molecular characteristics of these tumors remain largely undescribed. In this study, we performed a multi-platform molecular analysis of GCTs with SM diagnosed in 36 male patients (primary site: testis, 29 and mediastinum, 7). The most common histologic types of SM were sarcoma and embryonic-type neuroectodermal tumor (ENT, formerly known as "PNET"), present in 61% and 31% of cases, respectively. KRAS and TP53 mutations were identified by DNA sequencing in 28% of cases each, with enrichment of TP53 mutations in mediastinal tumors (86%). Gains in the short arm of chromosome 12 were seen in 91% of cases, likely reflecting the presence of isochromosome 12p. Numerous copy number changes indicative of widespread aneuploidy were found in 94% of cases. Focal homozygous deletions and amplifications were also detected, including MDM2 amplifications in 16% of cases. Sequencing of paired samples in 8 patients revealed similar mutational and copy number profiles in the conventional GCT and SM components. Oncogenic gene fusions were not detected using RNA sequencing of SM components from 9 cases. DNA methylation analysis highlighted the distinct methylation profile of SM components that sets them apart from conventional GCT components. In conclusion, GCT with SM are characterized by widespread aneuploidy, a distinct epigenetic signature and the presence of mutations that are otherwise rare in testicular GCT without SM. The similarity of the mutational and DNA methylation profiles of different histologic types of SM suggests that the identification of SM components could be more important than their precise histologic subclassification, pending confirmation by further studies.

Testicular Tumors: New Developments in Germ Cell and Sex Cord Stromal Tumors

This article reviews the recent advances and potential future changes in the classification of testicular germ cell and sex cord stromal tumors, highlighting changes in the classification system and terminology with description on newer entities. A discussion on approaching difficult areas and diagnostic pitfalls is also included along with the utility of ancillary investigations. Areas with limited knowledge are highlighted to providing direction for future studies and a bulleted summary in the form of critical care points is provided.

[Diagnostic problems in testicular tumours in consultant pathology : A practical guide]

The great variety of pathological patterns in germ cell tumours, especially in yolk sac tumours but also the possibility of somatic-type malignancies, can complicate daily diagnosis. For the correct diagnosis, knowledge of morphological aspects and additional immunohistochemical staining can be helpful. Also, rare entities like sex cord stromal tumours, tumours of testicular adnexa or mesenchymal tumours of the spermatic cord can be diagnostically challenging.

Atypical cartilage in type II germ cell tumors of the mediastinum show significantly different patterns of IDH1/2 mutations from conventional chondrosarcoma

Neoplastic cartilage is a common component of teratomas in type II germ cell tumors. Although IDH1/2 mutations have been well-described in somatic cartilaginous tumors, ranging from benign enchondromas to highly aggressive dedifferentiated chondrosarcomas, the presence of IDH1/2 mutations in cartilaginous neoplasms arising from germ cell tumors has not been previously investigated. To better understand the relationship between these tumors and their bone/soft tissue counterpart, we studied the IDH1/2 mutational status of 20 cases of primary mediastinal mixed germ cell tumors with areas of readily identifiable cartilaginous differentiation. Our study found that cartilaginous lesions arising in germ cell tumors have a different frequency and distribution of IDH1/2 mutations compared to those at somatic sites. We identified IDH1/2 mutations in only 15% (3/20) of cases, compared to a frequency in the literature among differentiated chondroid tumors of bone and soft tissue of 54%, a highly significant decreased frequency (p = 0.0011; chi-square test). Furthermore, they were exclusively IDH2 R172 mutations that occurred at a non-significant, increased frequency in the germ cell tumor group compared to conventional chondrosarcoma (15% vs. 5%, respectively, p > 0.05, chi-square test). The unexpected finding, therefore, was entirely attributable to the absence of IDH1 R132 mutation in chondroid neoplasia of germ cell origin (p < 0.00001, Fisher exact test). Our results suggest that a subset of cartilaginous lesions arising within type II germ cell tumors have a similar oncogenic mechanism to their bone/soft tissue counterpart but that the majority form using different oncogenic mechanisms compared to their somatic counterparts.

[New 2022 WHO classification of testicular tumours]

The 5th edition of the WHO Classification of Tumours: Urinary and Male Genital Tumours includes some important revisions of the testicular tumour classifications, which are summarized in this article. They concern, for example, the definition of tumours of neuroectodermal and neuroendocrine origin. Furthermore, signet-ring stromal tumours and myoid gonadal stromal tumours are listed as separate entities in the section about sex-cord stromal tumours. Moreover, lymphatic neoplasia as well as soft tissue tumours of the urinary and male genital tract are each combined in a common section.

Somatic-Type Malignancies in Testicular Germ Cell Tumors

The development of somatic-type malignancy (SM) in testicular germ cell tumor represents a major challenge in the diagnosis and treatment of testicular cancer. Most SMs are derived from teratoma, and the remainder is associated with yolk sac tumor. They occur more frequently in metastases than in primary testicular tumors. SMs demonstrate a variety of histologic types, including sarcoma, carcinoma, embryonic-type neuroectodermal tumor, nephroblastoma-like tumor, and hematologic malignancy. Sarcoma, particularly rhabdomyosarcoma, accounts for the majority of SMs in the primary testicular tumors, whereas carcinoma, particularly adenocarcinoma, is the most common SM in metastases. Although SMs derived from testicular germ cell tumors mimic their histologic counterparts in other organs with overlapping immunohistochemical profiles, isochromosome 12p is present in most SMs, which can be useful in the differential diagnosis. The presence of SM in the primary testicular tumor may not worsen the outcome, but the development of SM in metastasis is associated with a poor prognosis. Furthermore, somatic-type carcinoma is likely associated with a worse prognosis than somatic-type sarcoma. Although SMs respond poorly to the cisplatin-based chemotherapy, timely surgical resection is an effective treatment for most patients.

Germ cell tumors with neuroglial differentiation do not show molecular features akin to their central nervous system counterpart: experience from extra-gynecological sites

Teratomas with secondary somatic malignancy showing neuroglial differentiation (central nervous system (CNS)-type tumors) arising from a glial or neuroepithelial component is a very uncommon event and primarily described in the ovary. We aimed to describe the morphological spectrum and molecular features of CNS type of neuroepithelial tumors arising from the germ cell tumors (GCT) in the extra-gynecological sites. All cases of teratoma and mixed GCT arising from the non-gynecological sites over 7 years were screened for CNS type of neuroepithelial tumors. Detailed histological and immunohistochemical analysis was performed. IDH1 and 2 sequencings were performed in the glial tumors. Fluorescent in situ hybridization (FISH) was performed for EWSR1 rearrangement, 19/19q co-deletion, CDKN2A homozygous deletion, EGFR amplification, and C19MC amplification, wherever required. Out of 302 GCTs examined, the neuroglial tumor was detected in 15 cases. It included nine cases of glial tumors (including one pilocytic astrocytoma (grade I), two diffuse astrocytomas (grade II), one oligodendroglioma (grade II), one gemistocytic astrocytoma (grade II), three anaplastic astrocytomas (grade III), and one case of glioblastoma (grade IV)) and six cases of the embryonal tumor with multilayered rosettes (ETMR). None of the gliomas showed IDH mutation by immunohistochemistry or sequencing. The ETMR cases did not show Lin28 expression or C19MC amplification. To conclude, the spectrum of neuroglial tumors arising from teratoma in the extragonadal sites is vast and most commonly includes glial neoplasms and embryonal tumors. Our findings indicate that the genotype and pathogenesis of tumors with neuroglial differentiation in teratoma are distinct from their CNS counterpart.

Sarcomatoid Yolk Sac Tumor Harbors Somatic Mutations That Are Otherwise Rare in Testicular Germ Cell Tumors

In testicular germ cell tumors (TGCTs), components with nonspecific sarcomatous features that express keratins and glypican 3 are classified as sarcomatoid yolk sac tumor (SYST). SYST is most frequently seen in metastatic sites after chemotherapy. Like so-called "somatic-type" malignancies arising in TGCTs, SYST is markedly resistant to systemic therapy and has a more aggressive clinical course than conventional types of TGCT. However, the clinicopathologic and molecular features of SYST remain incompletely described. This study evaluated a multi-institutional series of 20 SYSTs using massively parallel sequencing and p53 immunohistochemistry. The histologic and clinical characteristics of the cases were also assessed, including analyses of disease-specific outcomes. DNA sequencing identified somatic mutations in 12/20 cases (60%), including recurrent TP53 and RIF1 mutations (present in 4/20 cases, 20% each). In 3 of the 4 SYST with TP53 mutations, there was molecular evidence of loss of heterozygosity. Immunohistochemistry demonstrated diffuse overexpression of p53 protein in 3/4 (75%) cases with TP53 mutations. The remaining TP53-mutant case demonstrated multifocal overexpression of p53, suggestive of subclonal inactivation of the gene. Overexpression of p53 protein was not seen in any of 15 TP53 wild-type cases evaluated by immunohistochemistry. A subset of 4 cases underwent RNA sequencing (fusion panel), which demonstrated the absence of oncogenic gene fusions. A 2-tiered grading system based on 3 histologic parameters (cellularity, number of mitoses, and necrosis) demonstrated that high-grade SYSTs have a higher risk of disease-specific death compared to low-grade tumors. The risk of disease-specific mortality was also higher in SYSTs with somatic mutations. In conclusion, this study demonstrated that 60% of SYSTs harbor somatic oncogenic mutations that are otherwise rare in TGCTs, and the presence of these mutations is associated with an aggressive clinical course. In addition, the results presented herein suggest that grading SYSTs may be clinically relevant.

Morphological spectrum and molecular features of somatic malignant transformation in germ cell tumours

AIMS

Somatic malignant transformation (SMT) arising in germ cell tumours (GCTs) is an infrequent, but clinically relevant event. There is only limited knowledge on the morphological spectrum of SMT, and therapeutic management of these patients is poorly defined. In this work we revisit two consecutive case series (n=756) of GCTs. Clinicopathological data of SMT arising in GCT were determined, with focus on the histopathological spectrum, and molecular aspects were obtained by Fluorescence in situ Hybridization (FISH) and Next Generation Sequencing (NGS).

METHODS AND RESULTS

30 male patients (28 primary testicular, 2 primary extragonadal) were included. These patients represent 4% of GCT patients diagnosed in two institutes (University Hospital Zurich and IPO Porto). The most common SMT were adenocarcinoma (n=8), embryonic-type neuroectodermal tumours (ENETs, n=8) and rhabdomyosarcoma (n=6), but a wide range of challenging morphologies were depicted, including low-grade neuroglial tumour, adenosquamous carcinoma, neuroblastoma and neuroendocrine carcinoma. SMT was found in 15 primary tumour samples and in 27 metastatic samples of these 30 patients, the latter showing poorer overall-survival. Adenocarcinoma occurred only in metastasis post-chemotherapy and in one primary retroperitoneal GCT with SMT, but not in GCT of the testis. 12p gains were identified by FISH in all cases. NGS results were available in 6 patients. Clinical trials and/or targeted treatments based on the molecular profile of SMT were recommended in 4 patients.

CONCLUSIONS

SMT arising in GCTs represents a diagnostic challenge and should be confirmed by a specialized uropathologist. NGS based treatment recommendations may improve outcome of these patients.

Carcinosarcoma of the stomach: four cases that expand the morphologic spectrum of gastric cancer with a primitive phenotype

Carcinosarcoma of the stomach is a rare neoplasm characterized by the presence of both epithelial and mesenchymal malignant components. We describe four examples with a focus on the characterization of the epithelial components and the histogenetic implications for this unique tumor. All patients were men aged 40-79 years. All patients developed metastatic disease, and three of them died 4-19 months after the diagnosis. Sarcomatous elements included poorly differentiated spindle cell sarcoma without distinctive differentiation (n = 4), chondrosarcoma (n = 2), and rhabdomyosarcoma (n = 1). In two cases, the sarcomatous component was recognized only in metastatic lesions. Notably, carcinomatous components were characterized by multilineage and primitive cellular differentiation, including carcinoma with enteroblastic (n = 4), hepatoid (n = 3), yolk sac tumor-like (n = 1), trophoblastic (n = 1), and neuroendocrine (n = 1) differentiation, as well as conventional tubular adenocarcinoma (n = 4). On immunohistochemistry, all four cases showed varying degrees of positive expression of primitive phenotypic markers, including alpha-fetoprotein (AFP), glypican-3, or SALL4. All tumors showed mutant patterns of p53 staining, exhibiting either diffusely positive or completely negative staining. On the basis of these findings, at least some gastric carcinosarcomas are likely to be derived from carcinoma with a primitive phenotype, including AFP-producing adenocarcinoma. Our observations suggest that sarcomatous differentiation, as well as multilineage differentiation of epithelial components, may represent increased cellular plasticity of gastric carcinoma with a primitive phenotype.

Somatic-type Malignancies in Testicular Germ Cell Tumors: A Clinicopathologic Study of 63 Cases

The development of somatic-type malignancies (SMs) in testicular germ cell tumors (GCTs) is a rare but well-recognized phenomenon. We studied the pathologic features of 63 GCTs with SMs in the testis (n=22) or metastases (n=41) and correlated these features with clinical outcomes. The patients with SMs in the testis (median age, 26 y) were younger than those with metastatic SMs (median age, 38.5 y). The SMs consisted of carcinomas (n=21), sarcomas (n=21), primitive neuroectodermal tumors (n=15), nephroblastomas (n=3), and mixed tumors (n=3). Sarcoma was the most common SM in the testis (n=11), and most sarcomas were rhabdomyosarcomas (n=9). Carcinoma was the most common SM in metastases (n=20), and most carcinomas were adenocarcinomas (n=12). In metastases, carcinomatous SMs developed after a longer interval from the initial orchiectomy (median times, 213 mo) than sarcomatous SMs (median times, 68 mo). Patients with metastatic SMs had significantly poorer overall survival than those with SMs in the testis (5-y survival rate, 35% vs. 87%; P=0.011). Furthermore, patients with carcinomatous SMs had a significantly worse prognosis than those with sarcomatous or primitive neuroectodermal tumor SMs (5-y survival rates, 17%, 77%, and 73%, respectively; P=0.002), when the whole cohort, including testicular and metastatic SMs, were analyzed. Our results demonstrate that SMs in metastatic GCTs are associated with a significantly worse prognosis than those in the testis. Furthermore, the histologic subtype of SM has a significant effect on the clinical outcome, with the carcinomatous SM carrying the highest risk for mortality.

Pure primary yolk sac tumor of the endometrium tends to occur at a younger age: A case report and literature analysis

We present a case of primary yolk sac tumor of the endometrium. This rare tumor occurred in a 43-year-old woman with a pure primary yolk sac tumor. The tumor resembled yolk sac tumor morphology of the ovary. Tumor cells expressed SALL4, AFP, GPC-3, and AE1/AE3 and were focal positive for PAX8. EMA, ER, and PR, among others, were negative. We further analyzed 29 reported cases of this rare tumor in the literature. In total, 17 of 30 patients (57%) had pure endometrial yolk sac tumor, and 13 (43%) had a concomitant somatic neoplasm (endometrial adenocarcinoma was the most common). Although the average age was 52 years (range: 24–87 years), patients with pure yolk sac tumor were younger than those with concomitant somatic tumors, with a mean age of 44.41 years (24–68 years) versus 61.92 years (28–87 years), P = 0.008. Patients with endometrial yolk sac tumor combined with somatic tumor tend to have a slightly higher stage and a poor prognosis.

Case Report: The Complete Remission of a Mixed Germ Cell Tumor With Somatic Type Malignancy of Sarcoma Type With a GCT-Oriented Therapy: Clinical Findings and Genomic Profiling

Somatic malignant transformation in a germ cell tumor (GCT) is the development of non-germ malignancies; much of available literature refers to teratoma with malignant transformation (TMT). There are various transformation histologies such as sarcoma, adenocarcinoma, primitive neuroectodermal tumors, and more rarely carcinoid tumors, hemangioendothelioma, lymphoma, or nephroblastoma. The treatments of these entities include surgery and/or chemotherapy. A standard approach in choosing chemotherapy in TMT cases has not yet been established. Many authors suggest using chemotherapeutic agents based on the transformed histology, while others recommend GCT-oriented therapy combined with surgery as the primary treatment, reserving histology-driven chemotherapies for metastatic relapse. We report the clinical findings and the genomic profile of a mixed GCT case with somatic-type malignancy of sarcoma type. We achieved a complete radiological response with GCT-oriented chemotherapy performed as salvage therapy after sarcoma-histology therapy. In addition, molecular profiles with RNA-sequencing and exome sequencing analyses of the primary tumor and the tumor with somatic-type malignancy of sarcoma type were explored.

Immunophenotypic Characterization of Germ Cell Tumor-Derived Primitive Neuroectodermal Tumors: Evidence for Frequent Neuronal and/or Glial Differentiation

CONTEXT.—

Primitive neuroectodermal tumors (PNETs) may arise as a somatic-type malignancy in germ cell tumors. In this setting, most PNETs resemble those of the central nervous system and lack chromosome 22 translocations. However, description of the morphologic and differentiation spectrum of PNETs arising from germ cell tumors is lacking.

OBJECTIVE.—

To investigate the morphologic and immunohistochemical features of these tumors, concentrating on neuronal and glial features.

DESIGN.—

We selected cases based on a morphologically identifiable glial and/or differentiated neuronal component in association with the undifferentiated PNET. Immunohistochemistry for glial fibrillary acidic protein, S100 protein, synaptophysin, chromogranin A, and SOX11 was performed on tumors with available material, with the scoring of both staining intensity (0-3) and extent (0-3). Thirteen qualifying PNETs of testicular origin with available immunohistochemical stains or stainable material were identified. The complete stain panel was performed in 10 tumors.

RESULTS.—

SOX11 demonstrated positive staining in the undifferentiated PNET component of all tumors (10 of 10) and was rarely positive in the differentiated (ie, neuronal/glial) component (1 of 10; focal and weak); synaptophysin was slightly less sensitive in the undifferentiated component (12 of 13; often focal and weak) and also showed positivity in the neuronal/glial component (5 of 13). Glial fibrillary acidic protein and S100 were more frequently positive in the differentiated areas (83% and 77%, respectively) compared with undifferentiated areas (25% and 17%, respectively).

CONCLUSIONS.—

SOX11 is a sensitive immunohistochemical marker for testicular PNET, particularly those lacking differentiation. Testicular PNETs often demonstrate glial and/or neuronal differentiation. Differentiation is marked by the acquisition of S100 and glial fibrillary acidic protein expression and SOX11 loss.

Non seminomatous mixed germ cell tumor of the testis with predominant component of somatic type malignancy (Rhabdomyosarcoma) - A rare occurrence

Testicular germ cell tumors (GCT) are a diverse group of neoplasms, broadly divided into seminomatous and non seminomatous types, with varying histomorphology. Mixed germ cell tumors express more than one germ cell component. Somatic type malignancy occurring in testicular GCT is rare. Most often these components present as metastasis, particularly following chemotherapy, rather than primarily involving the testis. We describe a rare case of a young adult with no significant past history, who presented with testicular mass which on histology revealed a non-seminomatous mixed germ cell tumor with additional somatic type malignancy component of a rhabdomyosarcoma.

The decisive role of molecular pathology in presumed somatic metastases of type II testicular germ cell tumors: report of 2 cases

Background

Molecular diagnostics can be decisive in the differential diagnosis between a somatic metastasis of type II testicular germ cell tumor (TGCT) or a second primary carcinoma. This is in line with recent recommendations from the International Society of Urological Pathology, based on an international survey which showed that molecular testing is currently only performed by a minority of urological pathologists.

Case presentations

This case report illustrates the necessity of molecular testing in two patients with a history of type II TGCT and a metastatic (retro) peritoneal carcinoma years later. The genetic hallmark of type II TGCT, chromosome 12p gain, was studied by fluorescence in situ hybridization and whole genome methylation profiling in case 1, and by single nucleotide polymorphism (SNP)-array in case 2. Next generation sequencing (NGS) was used to further explore clonality between the primary TGCT and peritoneal metastasis in case 2. In case 1, chromosome 12p gain was found in the primary type II TGCT and in the acinar cell carcinoma of the metastatic malignancy. In case 2, SNP array showed 12p gain in the epithelial component of the primary teratomatous TGCT but not in the peritoneal adenocarcinoma. Furthermore, NGS showed no mutations in the primary teratomatous TGCT but a KRAS and GNAS mutation in the peritoneal adenocarcinoma, suggestive of an appendicular origin.

Conclusions

Without the molecular data, both cases would have been regarded as a metastatic TGCT with development of somatic-type malignancy, which appeared a wrong diagnosis for case 2. These cases demonstrate the importance of molecular methods as an adjunct in today’s pathology practice.

Fluorescent In Situ Hybridization Analysis for 12p Alterations in Sarcomatoid Yolk Sac Tumors

"Sarcomas" in patients with testicular germ cell tumors (GCTs) are a common form of "somatic-type malignancy." There is support, based on morphology and immunohistochemistry, that many such sarcomatous tumors represent an unusual form of yolk sac tumor (YST). A virtually universal chromosomal anomaly in GCTs is increase in 12p copy number, often in the form of isochromosome 12p [i(12p)], but this aspect of sarcomatoid YSTs has not hitherto been studied. We performed interphase fluorescent in situ hybridization assay for detection of increased 12p copy number in sarcomatoid YSTs using a bacterial artificial chromosome-derived probe localized to 12p12.1 and a commercially available centromeric probe. Sixteen formalin-fixed, paraffin-embedded specimens from 11 patients, along with normal controls, were studied. Overrepresentation of 12p was expressed as a ratio between the number of signals for 12p and the number of signals for centromere 12. A ratio ≥1.3 was considered overrepresentation. All cases were postchemotherapy recurrences or metastases. Ages ranged 22 to 38 years (mean: 36). Most tumors (12/16) showed myxoid or fibromyxoid stroma and 15 of 16 were high grade. Thirteen of 16 specimens (81%) showed overrepresentation of 12p by the above criteria. Two cases exhibited loss of 12p and 1 case had gain of a whole chromosome 12 (trisomy 12). We conclude that, as in other GCTs, sarcomatous differentiation of YST demonstrates 12p alterations that can be identified by interphase fluorescent in situ hybridization. Apart from 12p overrepresentation, these tumors may exhibit loss of 12p or even gain of an entire chromosome 12 (trisomy 12). Increase in 12p copy number of a sarcomatous neoplasm provides support for sarcomatoid YST in clinically ambiguous settings.

Postchemotherapy sarcoma as a somatic-type malignancy derived from the gonadal yolk sac tumor in a patient with 46, XY pure gonadal dysgenesis

46, XY pure gonadal dysgenesis (PGD) is characterized as a female phenotype with strip-like gonads, which has a high tendency to develop into gonadal tumors. Somatic-type malignancies of germ cell tumors (SMs of GCTs) refer to the presence of malignant non-germ cell histologies admixed with GCTs, which are usually chemoresistant and indicate poor prognosis. This case report aimed to analyze the special histological type of GCTs and the importance of salvage surgery in the treatment of refractory GCTs. We report a unique case of gonadal yolk sac tumor (YST) transformed into SMs in a patient with 46, XY PGD. This 18-year-old woman underwent laparoscopic pelvic tumor resection, considered her first surgery, 2 years ago, and pathology revealed YST with initial alpha-fetoprotein (AFP) level measuring >3,000 ng/mL. She underwent seven cycles of chemotherapy, and the AFP level decreased to within a normal range after the second cycle. However, a computed tomography scan after the seventh cycle revealed abdominal and pelvic metastases, and vaginal bleeding was continuously observed. Laparoscopic exploration and laparotomy with tumor subtotal resection were performed. A pathology report showed SMs (sarcoma) derived from YST. Whole exome sequencing demonstrated that the main somatic mutation was a non-synonymous mutation of KRAS (c.182A>G), and this result did not show any indications for targeted drugs. She received three cycles of PEI (cisplatin, etoposide, and ifosfamide) chemotherapy but showed no response. She refused to undergo further treatment and has been alive with the disease for 7 months. This suggests that SMs may be one of the reasons for chemoresistance of refractory GCTs, and salvage surgery may be one of the most effective treatments for this patient. Targeted therapy may be a new choice for chemoresistant GCTs, but drug selection must be based on gene sequencing, and its efficacy still needs to be verified by further study.

Pitfalls in the interpretation of specimens from patients with testicular tumours, with an emphasis on variant morphologies

Accurate diagnosis of primary and metastatic tumours is essential in testicular cancer. While many cases are straightforward, some pose difficulties, especially when variant morphologies occur. Seminoma with 'atypical' features, including increased nuclear pleomorphism and crowding and greater cytoplasmic density with loss of membrane definition, mimics embryonal carcinoma, although ancillary features (fibrous septa, lymphocytes) and immunohistochemistry are of great help. Other deceptive seminoma features include prominent to exclusive intertubular growth, microcystic/tubular patterns, and signet-ring tumour cells. Conversely, embryonal carcinomas may have 'seminoma-like' foci, as may Sertoli cell tumours with diffuse growth and pale cytoplasm. Solid pattern yolk sac tumour mimics seminoma and, conversely, microcytic seminoma resembles yolk sac tumour. Other architectural patterns, ancillary yolk sac tumour features (intercellular basement membrane deposits, hyaline cytoplasmic globules) and immunohistochemistry aid in distinction from seminoma. Embryonal carcinomas may show, in addition to 'seminoma-like' foci, pseudoendodermal sinus-like structures, sieve-like patterns, endometrioid-like morphology and prominent zones of stratified columnar tumour cells. These may cause confusion with yolk sac tumour and teratoma, although careful attention to cytological features usually suffices for accurate diagnosis. Recent work has defined 'new' primary trophoblastic tumours, i.e., cystic trophoblastic tumour and epithelioid trophoblastic tumour. The newly termed 'spermatocytic tumour' occasionally consists mostly of a monotonous proliferation of intermediate-sized tumour cells with prominent nucleoli, thereby simulating either seminoma or embryonal carcinoma. Prostatic adenocarcinoma remains the most common tumour to metastasise to the testis and can cause confusion with rete carcinomas and primary germ cell tumours. Post-chemotherapy resections pose their own challenges. Effete tumour cells in areas of necrosis and prominent fibroxanthomatous reactions should not be interpreted as persistent, viable germ cell tumour. 'Fibrosis' often has atypical widely scattered spindle tumour cells in a densely collagenous background but does not merit additional treatment apart from excision. The marked cytological atypia that may occur in metastatic teratoma may be disconcerting but, again, the proper treatment is complete surgical excision rather than more chemotherapy. Glandular and sarcomatoid yolk sac tumours, which are almost exclusively seen after chemotherapy, resemble adenocarcinomas and sarcomas, respectively. Unlike de novo malignancies, they are mostly seen in sites expected for metastases.

ZBTB16 is a sensitive and specific marker in detection of metastatic and extragonadal yolk sac tumour

AIMS

Accurate histological diagnosis and classification of germ cell tumours (GCTs) is key to informing successful therapeutic and surveillance strategy. The modern therapeutic approach for yolk sac tumour (YST) is highly curative. Because YST takes on a large morphological spectrum, it can be confused for other GCT subtypes as well as somatic carcinomas, particularly when YST presents in an extragonadal or a metastatic setting. Currently available immunohistochemical markers are limited by suboptimal sensitivity and specificity. We reported recently that ZBTB16 is a sensitive and specific marker for testicular YST. ZBTB16 is absent in other GCTs and in most common somatic carcinomas, including those of gastrointestinal, pancreatobillary, respiratory, genitourinary and gynaecological tracts. The purpose of this study is to investigate the diagnostic utility of ZBTB16 in the settings of metastatic and extragonadal YST.

METHODS AND RESULTS

We studied 32 archived metastatic and four extragonadal primary YSTs as well as 51 somatic malignancies for their immunohistochemical expression of ZBTB16. For comparison, α-fetoprotein (AFP) and glypican-3 were also studied in parallel. Our results demonstrated an overall sensitivity of 91.6% for ZBTB16 in detecting metastatic and extragonadal YSTs. The non-YST elements (teratoma and embryonal carcinoma) in 15 YST-containing metastatic mixed GCTs were non-reactive. With the exception of occasional myoepithelial cells of salivary gland carcinoma, all the 51 somatic malignancies were negative for ZBTB16.

CONCLUSIONS

ZBTB16 is a sensitive and specific marker for YST and is diagnostically superior to AFP and glypican-3 in metastatic and extragonadal settings.

Two Tumors in 1: What Should be the Therapeutic Target? Pediatric Germ Cell Tumor With Somatic Malignant Transformation

BACKGROUND

Germ cell tumors with somatic malignant transformation (GCT with SMT) are rare in children and poorly described. Data are missing to determine if therapies should target the GCT, the SMT compound, or both simultaneously.

PATIENTS AND METHODS

A retrospective national study was conducted in the Société Française des cancers de l'Enfant (SFCE) Centers. Medical records from patients aged 0 to 18 years diagnosed with GCT with SMT between 2000 and 2015 were analyzed. Any stages and primary sites were considered as well as synchronous and metachronous cases.

RESULTS

Fifteen patients were identified. Thirteen patients had synchronous GCT with SMT. In the latter cases, primaries were ovary (5), mediastinum (3), pineal gland (3), sacrococcyx (1), and parametrium (1). SMT histologies were central primitive neuroectodermal tumor (5), embryonal rhabdomyosarcomas (3) or thyroid papillary adenocarcinoma, leukemia, poorly differentiated carcinoma, mixed sarcomas, and miscellaneous histology (1 case each). Chemotherapy was targeted against the GCT (3), the SMT (6), or both components (3). The last patient received surgery exclusively. Partial or complete response to chemotherapy was observed in 5/10 assessable cases: 2/3 patients treated with GCT-dedicated chemotherapy, 3/6 patients treated with SMT-dedicated therapy, and 0/1 treated with combined therapy. In addition, 2 patients with mediastinal GCT primary had metachronous SMT, with acute myeloid leukemia and thyroid papillary adenocarcinoma, 8 months and 8 years, respectively, after the diagnoses of GCT. Two patients (1 synchronous and 1 metachronous) were cured with surgery exclusively. At the end of follow-up, 6 patients died of their disease including all 4 with postsurgical macroscopic residue.

CONCLUSIONS

GCT with SMT constitutes a very rare entity in children and adolescents. Surgical removal of the tumor is the cornerstone of the treatment and might be sufficient in selected cases. In the remaining cases, the best management is still unknown and should take into account both components and their respective chemosensitivity. Long-term surveillance is advised for patient with unresected teratoma as late transformation can occur.

Pure Testicular Seminoma Relapsing Late with Somatic Type Malignancy

Background. Somatic type malignancy (STM) occurs in 2% of all germ cell tumours (GCTs). The prognosis is unfavourable and the origin is poorly understood. Pathogenetic hypotheses involve direct transformation of teratoma, origin from totipotent cancer cells, or derivation from yolk sac tumour elements. Case Presentation. A 31-year-old patient was cured from testicular seminoma clinical stage IIc by orchiectomy and cisplatin-based chemotherapy. Nine years later, he experienced a late relapse with a mass sized 5 × 6 cm located at the former metastatic site. As no remission occurred after chemotherapy with three cycles of cisplatin, ifosfamide and etoposide, the mass was surgically resected. Histologically, the specimen consisted of neurofibroma with areas of malignant peripheral nerve sheath tumour and spots with mature bone formation. FISH analysis disclosed isochromosome 12p in the majority of evaluated cells suggesting somatic type malignancy (STM) of GCT. The patient is well 1 year after surgery. Conclusion. The pathogenesis of this STM remains enigmatic. The origin from GCT was evidenced by documentation of isochromosome 12p. Unrecognized teratomatous elements in the primary and totipotent cancer cells surviving the first chemotherapy could be hypothesized to represent the origin. STM developing from seminoma cells would be another novel hypothesis.

CDX2 immunostaining in primary and metastatic germ cell tumours of the testis

Objective To evaluate the immunohistochemical staining pattern of caudal type homeobox 2 (CDX2) protein in germ cell tumours (GCTs) of the testis. Methods This study reassessed archival tissue samples collected from patients diagnosed with primary and metastatic testicular GCTs for CDX2 immunoreactivity using standard immunohistochemical techniques. Positive nuclear immunostaining was evaluated with regard to both the staining intensity and the extent of the staining. Results Tissue sections from primary and metastatic testicular GCTs ( n = 104), germ cell neoplasia in situ (GCNis) ( n = 5) and benign testicles ( n = 15) were analysed. The GCNis and benign testicular tissues showed no immunoreactivity for CDX2. Strong and diffuse staining of CDX2 was demonstrated only in the mature colonic epithelium of teratomas in both primary and metastatic GCTs. CDX2 positivity in other tumours (one pure yolk sac tumour, one yolk sac component of a mixed GCT and one pure seminoma) was infrequent, and was only weak and focal. Conclusions CDX2 immunostaining should be interpreted based on both the staining intensity and the extent of staining so as not to cause misdiagnosis. Teratomas with colonic-type epithelium should be considered in the differential diagnosis if a metastatic tumour with an unknown primary shows prominent CDX2 immunostaining.

High-level expression of divergent endodermal lineage markers in gonadal and extra-gonadal yolk sac tumors

Yolk sac tumors occur at both gonadal and extra-gonadal sites. A recent case of ovarian endometrioid-pattern yolk sac tumor with strong diffuse expression of TTF-1 illustrated the potential for misdiagnosis due to divergent expression of endodermal lineage markers. The aim of this study was to investigate the expression of four divergent endodermal lineage markers, TTF-1, CDX2, Hep Par 1, and Napsin A, in gonadal and extra-gonadal yolk sac tumors of differing age, sex, and location (excluding foci of overt hepatoid differentiation). We identified 26 cases (5 ovarian, 15 testicular, and 6 extra-gonadal) containing yolk sac tumor as identified by typical histology and confirmed by positive immunohistochemical staining for alpha-fetoprotein and glypican-3. Mixed or ambiguous foci were confirmed by immunohistochemistry (SALL4 positive and Oct-4 negative). The relative proportion of three histologic patterns: reticular/cystic, solid/myxoid, and glandular was estimated. Percent positivity for the four divergent endodermal lineage markers was compared within yolk sac tumor areas according to site, age group, and histologic pattern. High-level (>25%) staining for one or more divergent endodermal lineage markers was seen in eleven cases: Hep Par 1 in seven cases, all post-pubertal, TTF-1 in four cases, two ovarian and two extra-gonadal, and CDX2 in three cases, with no age or site predilection. No case highly expressed all three divergent endodermal lineage markers, but four co-expressed high levels of two markers: two ovarian yolk sac tumors with TTF-1 and Hep Par 1, one testicular yolk sac tumor with CDX2 and Hep Par 1, and one extra-gonadal yolk sac tumors with TTF-1 and CDX2. While no absolute correlation of high-level divergent endodermal lineage marker expression with histologic subtype was observed, TTF-1 and CDX2 expression was predominantly seen in reticular/cystic and glandular areas while Hep Par 1 was most frequent in myxoid/solid and glandular areas.

Tumors of the Testis: Morphologic Features and Molecular Alterations

This article reviews the most frequently encountered tumor of the testis; pure and mixed malignant testicular germ cell tumors (TGCT), with emphasis on adult (postpubertal) TGCTs and their differential diagnoses. We additionally review TGCT in the postchemotherapy setting, and findings to be integrated into the surgical pathology report, including staging of testicular tumors and other problematic issues. The clinical features, gross pathologic findings, key histologic features, common differential diagnoses, the use of immunohistochemistry, and molecular alterations in TGCTs are discussed.

ZBTB16: a novel sensitive and specific biomarker for yolk sac tumor

Although the function of zinc finger and BTB domain containing 16 (ZBTB16) in spermatogenesis is well documented, expression of ZBTB16 in germ cell tumors has not yet been studied. The aim of this study was to investigate the immunohistochemical expression and diagnostic utility of ZBTB16 in germ cell tumors. A total of 67 adult germ cell tumors were studied (62 testicular germ cell tumors, 2 ovarian yolk sac tumors, 1 mediastinal yolk sac tumor, and 2 retroperitoneal metastatic yolk sac tumors). The 62 testicular primary germ cell tumors are as follows: 34 pure germ cell tumors (20 seminomas, 8 embryonal carcinomas, 2 teratomas, 1 choriocarcinoma, 1 carcinoid, and 2 spermatocytic tumors) and 28 mixed germ cell tumors (composed of 13 embryonal carcinomas, 15 yolk sac tumors, 15 teratomas, 7 seminomas, and 3 choriocarcinomas in various combinations). Thirty-five cases contained germ cell neoplasia in situ. Yolk sac tumor was consistently reactive for ZBTB16. Among the 15 testicular yolk sac tumors in mixed germ cell tumors, all displayed moderate to diffuse ZBTB16 staining. ZBTB16 reactivity was present regardless of the histologic patterns of yolk sac tumor and ZBTB16 was able to pick up small foci of yolk sac tumor intermixed/embedded in other germ cell tumor subtype elements. Diffuse ZBTB16 immunoreactivity was also observed in 2/2 metastatic yolk sac tumors, 1/1 mediastinal yolk sac tumor, 2/2 ovarian yolk sac tumors, 2/2 spermatocytic tumors, 1/1 carcinoid, and the spermatogonial cells. All the other non-yolk sac germ cell tumors were nonreactive, including seminoma (n=27), embryonal carcinoma (n=21), teratoma (n=17), choriocarcinoma (n=4), and germ cell neoplasia in situ (n=35). The sensitivity and specificity of ZBTB16 in detecting yolk sac tumor among the germ cell tumors was 100% (20/20) and 96% (66/69), respectively. In conclusion, ZBTB16 is a highly sensitive and specific marker for yolk sac tumor.

The yolk sac tumor: reflections on a remarkable neoplasm and two of the many intrigued by it-Gunnar Teilum and Aleksander Talerman-and the bond it formed between them

One of the most remarkable of human neoplasms, the yolk sac tumor, is reviewed, emphasizing its histologic diversity and differential diagnosis, occurrence at many sites, and the shared passion for this unique neoplasm of Dr Gunnar Teilum (who deserves almost all credit for delineation of the nature of the tumor and its features) and Dr Aleksander Talerman (who made his own contribution to our knowledge of it) and the friendship it helped forge between these 2 distinguished pathologists. In a unique series of articles, beginning in the early 1940s, Teilum delineated the distinctive features of the neoplasm and recognized that it was 1 of 2 initially included as "mesonephroma ovarii" by Dr Walter Schiller in 1939 (the second we now know as clear cell carcinoma). Teilum named the tumor "endodermal sinus tumor" because it came to his attention that papillary formations common in the yolk sac tumor resembled the endodermal sinuses of the rat placenta. He focused on the histogenesis of the tumor and its morphologic features culminating in a classic paper in Cancer in 1959. Although Teilum and others recognized that yolk sac tumor could be a component of mixed germ cell tumors, Talerman was one of the first to emphasize that, particularly in the testis, it was common to see yolk sac tumor as a component of a mixed germ cell tumor. Teilum, working in Copenhagen, and Talerman, when the former was alive, working in Rotterdam, developed a warm friendship in part due to their great interest in the yolk sac tumor, although it also extended to other areas of gonadal neoplasia and indeed beyond the boundaries of medicine when they shared time together. The typical histologic features of the yolk sac tumor are the reticular-microcystic patterns Teilum described, but various other patterns, including solid and even rarer ones such as glandular and hepatoid, are now well known. There are some interesting variations in the age distribution of this tumor at various sites: for example, vaginal examples are almost restricted to children under 2 years of age; those of the testis that are pure also occur mostly in young boys (average age about 20 months) but are occasionally seen in later years; ovarian examples peak at about 19 years of age; mediastinal forms are mostly restricted to young adult males. Brief consideration is also given to the occurrence of this tumor at well-known extragonadal sites such as retroperitoneum, mediastinum, and pineal as well as more exotic locations. Note is made of the recently emphasized occurrence of the yolk sac tumor on the background of a somatic neoplasm, most often endometrioid carcinoma of the ovary. Given the wide ranging and fascinating clinical and pathologic aspects of the neoplasm, it is no surprise that it continues to be a source of great interest to any pathologist who sees one or more examples, and we are indebted to Dr Teilum for his monumental studies and to Dr Talerman for his own contributions.