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.

SMARCB1 (INI1)-Deficient Sinonasal Carcinoma with Yolk Sac differentiation Showing Co-loss of SMARCA4 Immunostaining - A Case Report and Literature Review

SMARCB1 (INI1)-deficient carcinoma of the sinonasal tract is a rare and distinct entity characterized by the loss of INI1 immunostain expression. These tumors are morphologically diverse, with isolated cases of yolk sac differentiation reported. We report the first case of SMARCB1-deficient sinonasal carcinoma that demonstrated co-loss of SMARCA4 immunostain, and reduced SMARCA2 and ARID1A staining, with the entire tumor showing histological and immunohistochemical evidence of yolk sac differentiation. The clinical, histological, immunohistochemical and molecular features were discussed and compared against SMARCB1-deficient sinonasal carcinomas with yolk sac differentiation and SMARCA4-deficeint sinonasal carcinomas reported in the literature. With a highly aggressive clinical course leading to mortality two months after presentation, the behavior of this tumor appears to be more comparable to that of SMARCA4-deficient sinonasal carcinomas. A comprehensive immunopanel including SMARCB1, SMARCA4, SMARCA2 and ARID1A may be advisable for assessment and prognostication of SWI/SNF-deficient tumors.

Urachal yolk sac tumor penetrating the bladder as a diagnostic challenge: a case report and review of the literature

Background

Yolk sac tumor (YST) is a germ cell tumor. It is primarily located in the gonads but can also occur extragonadally (extragonadal yolk sac tumor - EGYST), most commonly in the pelvis, retroperitoneum or mediastinum. Only a few YSTs of the urachus have been described.

Case report

We present a rare case report of a 37-year-old male with episodes of macroscopic hematuria. The histological specimen obtained by transurethral resection showed a solid, and in some parts papillary infiltrative, high-grade tumor with numerous areas of marked nuclear atypia and clear invasion between the detrusor bundles. Glandular pattern has been observed in only minority of the tumor. Immunohistochemistry showed significant positivity for GPC3, SALL4 and cytokeratins AE1/AE3, while KRT7 and GATA3 were negative. We concluded that the biopsy findings were consistent with urothelial carcinoma with infrequent YST differentiation. In definitive surgical specimens we found a malignant epithelial, glandular and cystically arranged tumor of germinal appearance arising from urachus. The surrounding urothelium was free of invasive or in situ tumor changes. We reclassified the tumor as a urachal YST.

Conclusion

EGYST was suspected because glandular and hepatoid structures were found, but the presence of these structures should be verified by immunohistochemistry.

Complete remission of Cdx-2 positive primary testicular carcinoid tumor: 10-years follow-up and literature review

BACKGROUND

The neuroendocrine cells can cause a variety of malignancies throughout the human body known as the neuroendocrine tumors (NETs) or carcinoid tumors. The primary testicular carcinoid tumor (PTCT) accounts for less than 1% of the testicular neoplasms and for only 0.2% of all carcinoid tumors representing already a very rare neoplastic entity. Here, we present a patient with a history of an exceptionally rare primary testicular carcinoid tumor, staining positive for Cdx-2 along with a literature review.

CASE PRESENTATION

A 44-year old patient without significant past medical history was diagnosed in September 2009 with primary testicular carcinoid tumor, which was surprisingly staining positively for Cdx-2, too. At the time of the initial diagnosis the tumor was already showing histopathological infiltration of veins. DOTA-TATE-PET/CT imaging and endoscopy studies did not show any signs of distant metastases and in particular no gastrointestinal manifestation following no further medical indication for systemic chemotherapy. The continuous and close follow-up of the patient has reached a total of over 10 years at the time of publication remaining in complete remission.

CONCLUSION

The diagnosis of primary testicular carcinoid is based on histopathology. The detailed histopathologic assessment of biomarkers based on immunohistochemistry is very important for the classification and the prognosis of the primary testicular carcinoid tumor. Primary testicular carcinoid tumor with Cdx-2 positive stain outlines an exceptionally rare neoplastic entity without a consensus about general follow-up guidelines, requiring close clinical and imaging aftercare and consideration in Cdx-2 positive metastatic tumor of unknown origin.

Primary Endometrial Yolk Sac Tumor With Endodermal-Intestinal Differentiation Masquerading as Metastatic Colorectal Adenocarcinoma

Yolk sac tumors (YSTs) with a somatic glandular pattern can be difficult to recognize histologically because they reproduce developing intestinal, hepatic, or lung tissue and can express markers such as CDX2 and TTF1. We report an unusual case of a primary endometrial YST showing florid endodermal-intestinal differentiation in a 63-yr-old woman with a history of colorectal adenocarcinoma. Histologically, the tumor exhibited a glandular and papillary architecture and showed widespread immunoreactivity for CDX2 and focal staining for CK20 and CEA, mimicking metastatic colorectal carcinoma on biopsy. The presence of subnuclear cytoplasmic clearing and positive staining for germ cell markers, however, pointed toward a diagnosis of primary endometrial YST, and this was supported by the radiologic and the subsequent pathologic finding of a primary endometrial-based lesion. YSTs in this age group usually arise in association with somatic tumors and in this case a small focus of coexistent endometrioid adenocarcinoma was identified within the uterus. Despite surgery and adjuvant chemotherapy, the patient showed disease progression with liver and lung metastases 6 mo postoperatively.

Yolk Sac Tumor in Extragonadal Pelvic Sites: Still a Diagnostic Challenge

We present the clinicopathologic features of 15 cases of extragonadal yolk sac tumor (EGYST) detected in female patients and reviewed at our institution from 1988 to 2016. We recorded: patient age, clinical presentation, tumor location, FIGO stage (where applicable), histologic patterns including presence/absence of Schiller-Duval bodies, other germ cell or somatic components, immunoperoxidase results, treatment, and outcome. Patients' ages ranged from 17 to 87 (median, 62) years and presentation included: abnormal uterine bleeding, 12; hematuria, 1; labial mass, 1; abdominal pain, 1. Primary sites were as follows: uterus (11), vagina (1), vulva (1), bladder (1), and peritoneum (1). Seven patients presented at FIGO stage III or IV. The following histologic patterns were observed: microcystic/reticular (7), glandular (8), solid (8), papillary (5), and hepatoid (1). An admixture of histologic patterns was present in 10 cases. Schiller-Duval bodies were seen in only 3 (23%) cases. Eight cases (46%), all uterine primaries, had associated somatic components, and 2 (15%) had a second germ cell component. In 13/14 (93%) cases, the yolk sac tumor component was either missed or misclassified as adenocarcinoma. Immunoperoxidase studies facilitated the diagnosis in all cases as follows: SALL4, 12/12; CDX2, 10/12; α fetoprotein, 7/14; glypican-3, 9/10; cytokeratin 20, 5/9 (rare cells); cytokeratin 7, 3/12 (nondiffuse); PAX8, 2/9 (variable expression). All patients received chemotherapy and all except 1 underwent surgical resection. Follow-up from 5 to 86 months was available for 13 patients: 5 died of disease, 6 are alive with disease, and 2 have no evidence of disease. EGYST arising in the female pelvis of peri/postmenopausal patients may be associated with a somatic component and represent either somatically derived YST or YST differentiation within a somatic carcinoma. EGYST in younger patients is likely a true germ cell neoplasm, and may respond to germ cell appropriate chemotherapy. The benefit of germ cell appropriate chemotherapy in somatically derived EGYST is less clear. Awareness that the presence of glandular or microcystic patterns may lead to under-recognition or misdiagnosis of EGYST in combination with immunomarkers for germ cell and yolk sac differentiation will facilitate the diagnosis.

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.

Ovarian Yolk Sac Tumor With High-Grade Serous Carcinoma in a 62-Year-Old Woman

Ovarian yolk sac tumors are germ cell tumors that usually present in children and young women. Rarely, these tumors can arise in older women, usually in conjunction with surface epithelial tumors, suggesting divergent differentiation from the latter. The combination of mixed ovarian yolk sac tumor and high-grade serous carcinoma is rare, with only one case documented in the literature. We present a case of mixed ovarian yolk sac tumor and high-grade serous carcinoma in a postmenopausal woman, including a brief discussion of the immunohistochemical findings and differential diagnosis. Despite the rarity of mixed ovarian yolk sac tumor and surface epithelial tumors, it is important to recognize the biphasic nature of the tumor, which should prompt a thorough immunohistochemical evaluation. The therapeutic and prognostic implications of proper diagnosis cannot be overemphasized.

Discovery and diagnostic value of a novel oncofetal protein: glypican 3

Glypican 3 is a membrane-bound heparan sulfate proteoglycan, which has recently been identified as a marker for liver cancer and germ cell malignancies. Individuals with loss-of-function mutations for the glypican 3 gene exhibit Simpson-Golabi-Behmel syndrome, a rare X-linked overgrowth disorder. Expression of glypican 3 mRNA and protein is normally silenced in most adult organs and may reappear during malignant transformation. In the past few years, immunohistochemical and molecular characteristics of glypican 3 in hepatocellular carcinoma have been elucidated. More recently, glypican 3 has been emerging as a new diagnostic marker for germ cell tumors and especially testicular and ovarian yolk sac tumors. However, in other tumors such as renal cell carcinomas, squamous cell carcinomas, and melanomas, studies disagree on the level of glypican 3 expression. Finally, there is the controversial notion of glypican 3 as a tumor suppressor gene. In this review article, we update current knowledge on glypican 3 expression in normal and neoplastic tissues, evaluate its utility as a tumor marker in clinical practice, and explore its role as a novel oncofetal protein with clinical implications. Our focus is on the diagnostic value of glypican 3 in germ cell tumors and other neoplasms in addition to hepatocellular carcinoma. In conclusion, glypican 3 has been proven to be a useful immunohistochemical marker in distinguishing yolk sac tumors, choriocarcinomas, and Wilms tumors from other malignancies histologically mimicking these primitive tumors. Clinically, we recommend that glypican 3 be used as part of a panel of markers in subtyping testicular germ cell tumors.

Germ cell tumors of the ovary: an update

CONTEXT

The field of ovarian germ cell tumors (OGCTs) has remained relatively unchanged in the last 2 decades. However, the introduction of new stem cell pluripotency markers has provided a new understanding into the identification and taxonomy of OGCT types. New data have provided new insights into unusual teratoma-associated autoimmune disorders and the origin of gliomatosis peritonei.

OBJECTIVE

To review the impact of new pluripotency markers in the diagnosis of malignant OGCT (MOGCT) and analyze new nomenclature proposals and clinicopathologic entities.

DATA SOURCES

Ovarian germ cell tumors from routine material and expert consultation files at San Cecilio University Hospital, Granada, Spain, and the relevant literature were reviewed.

CONCLUSIONS

Although a correct diagnosis of MOGCT can often be made with histologic and classic immunohistochemical studies, the new immunohistochemical pluripotency markers give higher diagnostic accuracy. Germ cell tumors represent a caricature of the phases of normal embryonic differentiation from primordial germ and stem cells to extraembryonal and somatic tissue differentiation. Since every stage of differentiation and its related tumor type exhibit characteristic markers, the analysis of their expression facilitates tumor typing, thus complementing the use of classic antibodies. They also allow a more precise evaluation of the degree of immaturity in teratoma. The new term, primitive endodermal tumors, simplifies the understanding of the complex histology of the yolk sac tumor group, as this terminology encompasses its multiple endodermal differentiations. Recently described autoimmune encephalitis due to antibodies against the N-methyl-d-aspartate receptor has become the most frequent autoimmune disorder associated with ovarian teratoma.

A diagnostic immunohistochemical panel for yolk sac (primitive endodermal) tumours based on an immunohistochemical comparison with the human yolk sac

AIMS

To establish a diagnostic immunohistochemical panel for various histotypes of yolk sac (primitive endodermal) tumours (YSTs) by comparison with the human yolk sac (HYS) immunophenotype.

METHODS AND RESULTS

Twenty-five YSTs showing either classical patterns (CPs) of histology (microcystic/reticular, n = 14; polyvesicular, n = 1; and hepatoid, n = 1) or somatic glandular patterns (SGPs; n = 9) were analysed for expression of α-fetoprotein (AFP), glypican-3 (GPC3), villin, hepatocyte paraffin-1 (HepPar-1), CDX2, SALL4 and LIN28. AFP expression was constantly heterogeneous in CPs but tended to be focal/absent in SGPs. GPC3 was diffuse in CPs but heterogeneous (seven cases) or focal/absent (two cases) in SGPs. HepPar-1 expression was focal in all but three cases (diffuse in one CP-hepatoid and two SGPs). CDX2 positivity was focal in CPs but heterogeneous (seven cases) or diffuse (two cases) in SGPs. Villin, SALL4 and LIN28 were diffusely positive in nearly all cases.

CONCLUSIONS

CPs reproduce the immunophenotype of HYS and early endoderm with variable expression of both AFP and markers of early gut or hepatic differentiation. SGPs with intestinal differentiation often have incomplete immunophenotypes. A differential diagnosis panel, including both markers of pluripotentiality (SALL4 and/or LIN28) and endoderm (AFP, GPC3 and villin), is proposed. It identifies overlapping multidifferentiation of primitive and somatic immunophenotypes, supporting the recently proposed term of primitive endodermal tumours.

Demonstration of CDX2 is highly antibody dependant

OBJECTS

CDX2 is a widely used immunohistochemical marker for intestinal differentiation in neoplasms. In the Nordic Immunohistochemical Quality Control external quality assessment scheme, only 45% of the laboratories participating in the CDX2 challenge in 2009 produced sufficient staining. A major cause of insufficient staining results appeared to be less successful primary antibody (Ab) clones. To evaluate the Ab performance in a standardized way, a comparative study was carried out.

MATERIALS AND METHODS

Tissue microarrays containing 309 non-neoplastic tissues and tumor samples with expected high, low, and no CDX2 expression were used. Five Abs were selected for comparison: EPR2764Y concentrated (Conc), EPR2764Y in a ready-to-use format, and DAK-CDX2, AMT28, and CDX2-88, all Conc. The CDX2 stains were scored blindly using the H-score method. Tissue/tumor samples with a maximum H-score of 150 to 300 (on the basis of the staining giving the highest score) were classified as CDX2 high expressors, samples with a maximum H-score of 10 to 149 as low expressors, and samples with a maximum H-score <10 as negative.

RESULTS AND CONCLUSIONS

A total of 106 tumors were CDX2 positive with at least one of the Abs. For 56 high-expressor tumors, the mean H-scores with EPR2764Y Conc, EPR2764Y ready-to-use, DAK-CDX2, AMT28, and CDX2-88 were 262, 236, 234, 167, and 149, respectively, and the percentage of positive tumors 100, 100, 100, 98, and 93, respectively. For 50 low-expressor tumors, the mean H-scores with the same Abs were 59, 26, 28, 7, and 5, respectively, and the percentage of positive tumors 98, 58, 64, 18, and 14, respectively. With EPR2764Y Conc, CDX2 was demonstrated in 5/19 (26%) urothelial carcinomas, 7/64 (11%) lung adenocarcinomas, 5/30 (17%) large cell/sarcomatoid lung carcinomas, and 4/19 (21%) esophagus squamous cell carcinomas. In-house optimized protocols gave for all 4 Conc Abs better staining results than the vendors' recommended protocols. The sensitivity of CDX2 Abs and protocols must be taken into consideration when classifying neoplasms of unknown origin.

CDX-2 expression in malignant germ cell tumors of the testes, intratubular germ cell neoplasia, and normal seminiferous tubules

CDX-2 is a caudal-type homeobox gene, encoding a transcription factor that plays an important role in proliferation and differentiation of intestinal epithelial cells. The utility of antibodies to CDX2 in the identification of adenocarcinomas of the gastrointestinal tract, particularly colorectal adenocarcinomas, in both primary and metastatic settings is well established. It is well-known that patients with testicular tumors may occasionally lack an obvious palpable mass. However, the expression of CDX2 in malignant germ cell tumors of the testes which have metastatic potential has not been previously studied in a large series. A tissue microarray was constructed from 52 malignant germ cell tumors of the testes including: 29 cases of classic seminoma, 8 cases of embryonal carcinoma, 8 cases of yolk sac tumor, 4 cases of malignant teratoma, 2 cases of choriocarcinoma, and 1 case of spermatocytic seminoma. Ten cases of intratubular germ cell neoplasia and seven cases of benign testicles with normal seminiferous tubules were also included in tissue microarray. Immunohistochemical stains for CDX2 was performed and analyzed. Only nuclear staining was considered positive. Positive expression of CDX2 was identified in 2/2 cases (100 %) of choriocarcinoma, 4/8 cases (50 %) of teratoma, 3/8 cases (38 %) of embryonal carcinoma, 3/8 cases (38 %) of yolk sac tumor, and 1/29 cases (3 %) of classic seminoma. CDX2 was negative in all cases of intratubular germ cell neoplasia, normal seminiferous tubules, and the only case of spermatocytic seminoma. The role of CDX-2 in the differentiation of intestinal/enteric epithelial cells may contribute to the formation of trophoblastic, glandular, villous, or cystic structures in germ cell tumors of the testes. This study suggests that the expression of CDX2 in a variety of malignant germ cell tumors of the testes may be a potential pitfall in metastatic tumors of unknown primary, which are thought to be of gastrointestinal/colorectal origin but are actually from a clinically occult testicular tumor.

Malignant mixed mullerian tumor: an immunohistochemical study

Malignant mixed Mullerian tumor (MMMT) is an uncommon aggressive neoplasm composed of both malignant epithelial and mesenchymal components. In this study, immunohistochemical stains of germ cell markers, including SALL4, OCT3/4, glypican-3, and alpha-fetal protein (AFP), and CDX2 were performed in a series of MMMTs. SALL4 nuclear immunoreactivity was detected in 6 out of 19 cases (33%). The staining extent ranged from focal to extensive. The staining intensity was usually intermediate to strong (the score ranged from 1.5 to 3, and average score was 2.3 ± 0.5 in the positive cases). In addition, glypican-3 cytoplasmic reactivity was detected in 14 out of 16 cases (88%) with a mean score of 1.8 ± 0.7 (score ranging from 1 to 3). In contrast, OCT3/4 was only positive in 1 out of 19 cases and AFP in 2 out of 18 cases (11%). In summary, SALL4 and glypican-3 were frequently expressed in a subset of MMMTs. Their roles in the pathogenesis and biology of MMMT are yet to be determined. MMMT should be included in the differential diagnosis when a tumor is positive for SALL4 and/or glypican-3.

CDX2 expression in columnar cell variant of papillary thyroid carcinoma

The columnar cell variant of papillary thyroid carcinoma (CCV-PTC) is a rare subtype of PTC that exhibits morphologic features often described as reminiscent of secretory endometrium or colonic adenomas/adenocarcinomas. CDX2, a nuclear transcription factor, is important for intestinal development. It is normally expressed in intestinal epithelium and is also detected in adenoma and adenocarcinomas of the gastrointestinal tract; however, it has also been reported in tumors of other sites with intestinal-type morphologic features. We evaluated CDX2 expression in CCV-PTC and in a thyroid tissue microarray composed of various benign and malignant thyroid lesions. CDX2 expression was identified in 6 (55%) of 11 cases of CCV-PTC, but not in any other benign and malignant thyroid lesions. We conclude that CDX2 is selectively expressed in CCV-PTC and can be used in distinguishing it from other variants of PTC with overlapping morphologic features.

Oral extragonadal yolk sac tumor in a patient with Aicardi syndrome: putative origin and differential diagnosis

We report, for the first time, a primary oral presentation of a germ cell yolk sac tumor in a 4-year-old girl with Aicardi syndrome. The diagnosis, differential diagnosis, and histogenesis are discussed.

Intratubular germ cell neoplasia of the testis and its associated cancers: the use of novel biomarkers

Recent advances in the understanding of the molecular pathology of testicular tumours have led to the identification of several new immunohistochemical markers for invasive and in situ germ cell neoplasms. OCT3/4 and NANOG are nuclear stains that have high sensitivity and specificity for the identification of intratubular germ cell neoplasia as well as seminoma and embryonal carcinoma. A potential pitfall in their application to the detection of intratubular germ cell neoplasia, as in other markers that represent oncofetal antigens, is their expression in non-neoplastic germ cells with 'delayed maturation'. SALL4, another nuclear stain, is positive for most germ cell tumours as a group and may be especially helpful in the distinction of these tumours from somatic carcinomas in non-testicular sites. Glypican 3 is a more sensitive marker for yolk sac tumour than alpha-fetoprotein. SOX2 and SOX17 may be useful for differentiating seminoma and embryonal carcinoma, especially following chemotherapy as embryonal carcinoma may lose CD30 expression in this setting. This article reviews the application of these immunohistochemical markers and others to the diagnosis of germ cell neoplasia with reference to older immunohistochemical stains when appropriate. Suggested immunohistochemical panels are described for individual tumour types.