Transformation of an AFP-positive yolk sac carcinoma into an AFP-negative neoplasm. Evidence for in vivo cloning of the human parietal yolk sac carcinoma

Germ Cell Tumor of the Testis: Lethal Subtypes of a Curable Cancer

Germ cell tumor of the testis (GCT) is a curable cancer even when it is widely metastatic; however, outcomes can differ based on tumor histology. Chemo-resistance in certain phenotypes, such as teratoma and yolk sac tumor, contributes to poor clinical outcomes in some patients with GCT. Despite this resistance to S-YSTemic therapy, many of these tumor subtypes remain amenable to surgical resection and possible cure. In this study, we report on a series of seven patients highlighting two chemo-resistant subtypes of nonseminomatous germ cell tumor (NSGCT), sarcomatoid yolk sac tumor (S-YST), and epithelioid trophoblastic tumor (ETT) for which early resection rather than additional salvage chemotherapy or high-dose intense chemotherapy might provide a superior clinical outcome and enhance cure rate.

Clinical Challenges in the Management of Malignant Ovarian Germ Cell Tumours

Nonepithelial ovarian cancers (NEOC) are a group of rare malignancies, including germ cell tumours (GCT) and sex cord-stromal tumours (SCST), along with small-cell carcinomas and sarcomas. GCTs represent 2-5% of ovarian cancers, with a yearly incidence of 4:100,000, and they usually affect young women and adolescents. Precursory germ cells of the ovary form the basis of GCT. They are histologically classified into primitive GCT, teratomas, and monodermal and somatic-type tumours associated with dermoid cysts. A primitive GCT can be either a yolk sac tumour (YST), dysgerminoma, or mixed germ cell neoplasm. Teratomas are either mature (benign) or immature (malignant). Given that malignant GCTs occur rarely compared to epithelial ovarian tumours (EOC), greater focus is required in their diagnosis and treatment. In this article, we review the epidemiology, clinical manifestations, diagnosis, and molecular biology, along with the management and therapeutic challenges.

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.

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.

Late recurrences of germ cell malignancies: a population-based experience over three decades

The purpose of this study was to explore the incidence of late relapse in patients with malignant germ cell tumour (MGCT) in a population-based series, with emphasis on the mode of detection, survival, and the relevance of histological findings. The clinical records from a population-based cohort of patients with seminoma (n=1123) or non-seminoma (n=826) were evaluated for late relapses. Twenty-five patients developed a late relapse. The cumulative 10-year incidence rate was 1.3%. All 10 seminoma patients, but only eight of 15 non-seminoma patients relapsed with vital malignant tumour (P=0.02). Teratoma or necrosis was found in seven of nine primarily chemotherapy-treated non-seminoma patients with normal tumour markers at late relapse. Six of nine patients operated with limited retroperitoneal lymph node dissection as part of the primary treatment had relapsed retroperitoneally outside the original operation field. The 10-year cause-specific survival was 68% in all patients, 50% in patients relapsing with vital malignant tumour and 100% in those with teratoma/ necrosis before or after salvage chemotherapy. The 10-year incidence rate of late relapses of 1.3% might reflect the true incidence rate in a population-based cohort of MGCT patients, with cure in at least half of them.

Germ cell tumors of the gonads: a selective review emphasizing problems in differential diagnosis, newly appreciated, and controversial issues

Gonadal germ cell tumors continue to be the cause of diverse, diagnostically challenging issues for the pathologist, and their correct resolution often has major important therapeutic and prognostic implications. They are academically interesting because of the biological diversity exhibited in the two gonads and variation in frequency of certain neoplasms. The most dramatic examples of the latter are the frequency of dermoid cyst in the ovary compared to the testis and the reverse pertaining to embryonal carcinoma. Within the teratoma group, there is strong evidence that ovarian and prepubertal testicular teratomas are derived from benign germ cells, a pathogenesis that likely applies also to the rare dermoid cysts and uncommon epidermoid cysts of the testis. In contrast, postpubertal testicular teratomas derive from malignant germ cells, specifically representing differentiation within a preexistent nonteratomatous cancer. As expected, given the foregoing, teratomas in boys are clinically benign, whereas in postpubertal males they are malignant, independent of their degree of immaturity. On the other hand, immaturity is an important finding in ovarian teratomas, irrespective of age, although its significance in children has recently been challenged. It is usually recognized on the basis of embryonic-appearing neuroepithelium, which shows mitotic activity and apoptosis in contrast to differentiated neuroepithelial tissues, which may occur in mature ovarian teratomas. Rarely it is based on the presence of cellular, mitotically active glial tissue. Fetal-type tissues alone are not sufficient for a diagnosis of immature teratoma. Further differences between the teratomatous tumors in the two gonads are the relative frequency of monodermal teratomas in the ovary in contrast to the testis, where only one subset, carcinoids, is seen with any frequency. When uncommon somatic-type malignancies (usually squamous cell carcinoma) occur in mature cystic teratomas of the ovary, this is a de novo form of malignant transformation; similar tumors in the testis, a very rare event, represent overgrowth of teratomatous elements that originated from malignant, nonteratomatous germ cell tumors and, therefore, had previously undergone malignant transformation. Germinomas may have several unusual features in each gonad; these include microcystic arrangements that suggest yolk sac tumor, tubular patterns that mimic Sertoli cell tumor, apparent increased cytological atypia that causes concern for embryonal carcinoma, and prominent syncytiotrophoblast giant cells that suggest choriocarcinoma. Awareness of these variants, good technical preparations, the retained typical cytological features of germinoma cells, and the judicious use of tailored panels of immunohistochemical stains resolve these dilemmas in virtually all instances. Two aspects of germinomas are unique to the testis. Firstly, intertubular growth of small seminomas may cause them to be overlooked. Secondly, the distinctive spermatocytic seminoma occurs only in the testis. A newly recognized aspect of this tumor is the propensity for some to be relatively monomorphic, making them apt to be mistaken for usual seminoma or embryonal carcinoma, although the characteristic polymorphic appearance in some foci, absence of intratubular germ cell neoplasia, unclassified type, and immunohistochemical stains should prevent this error. Cytoplasmic membrane immunoreactivity for placental alkaline phosphatase and CD117, with usual negativity for AE1/AE3 cytokeratins, is helpful in the diagnosis of germinoma. The recently described marker, OCT3/4, a nuclear transcription factor, is especially helpful in the differential of germinoma and embryonal carcinoma with other neoplasms. Yolk sac tumor continues to be confused occasionally with clear cell carcinoma of the ovary. Glandular ('endometrioid-like') yolk sac tumors mimic endometrioid carcinomas; predominant or pure hepatoid yolk sac tumors cause concern for metastatic hepatocellular carcinoma or, in the ovary, primary hepatoid carcinoma, and solid patterns, especially in limited samplings, may be misinterpreted as germinoma. The usually younger age of patients with yolk sac tumors helps with the differential considerations with the nongerm cell tumors, as do other clinical and microscopic features and selected immunohistochemical stains. Choriocarcinoma is rare in both gonads, and those in the ovary must be distinguished from metastatic tumors of placental origin. Syncytiotrophoblast cells alone, admixed with other forms of germ cell tumor, still are confused with choriocarcinoma, but this phenomenon, which is much more frequent than choriocarcinoma, lacks the plexiform arrangement of different trophoblast cell types that typifies the latter. Mixed germ cell tumors (which may show almost any combination of components) are common in the testis but rare in the ovary. A separately categorized, rare form of mixed germ cell tumor seen in both gonads is the polyembryoma. It is perhaps the most photogenic of all gonadal germ cell tumors and is also intriguing because of its distinctive, organized arrangement of yolk sac tumor and embryonal carcinoma elements and recapitulation of very early embryonic development, even to the extent of having in its fundamental unit, the embryoid body, a miniature yolk sac, and amniotic cavity. These tumors, which are constituted by innumerable embryoid bodies, almost always contain teratomatous glands in minor amounts, and one way of viewing the polyembryoma is to consider it the most immature form of teratoma. Embryoid bodies are also common as a minor component of many mixed germ cell tumors, particularly in the testis, and the diffuse embryoma is another variant that has a particular arrangement of yolk sac tumor and embryonal carcinoma elements. Regression of gonadal germ cell tumors is a phenomenon restricted to the testis, for unknown reasons. These so-called 'burnt-out' germ cell tumors can be recognized by a distinctive constellation of findings, including sometimes minor foci of residual recognizable germ cell neoplasia, a well-defined zone of scarring (often having residual ghost tubules), associated lymphoplasmacytic infiltrate, intratubular calcification and, in about 50%, of in situ germ cell neoplasia.

The pathology of late recurrence of testicular germ cell tumors

A total of 91 men had histologically documented late recurrences of testicular germ cell tumors characterized by a complete response to treatment with a subsequent disease-free interval of at least 2 years and no evidence of a second primary lesion. Ninety percent of the patients for whom information was available received chemotherapy shortly after their initial diagnosis of testicular germ cell tumors; most of the other patients were known to have stage I disease initially. Overall, 60% of patients had teratoma in their late recurrences, including 20 patients (22%) in whom teratoma was the only element. Thus, teratoma was the most common type of neoplasm in late recurrences. Excluding teratoma coexisting with other types of neoplasms, yolk sac tumor was the most frequent type of tumor in patients with late recurrence. It occurred in 47% of patients, either alone or with teratoma, another nonteratomatous germ cell tumor type, or a "nongerm cell malignant tumor." Unusual types of yolk sac tumor, including glandular, parietal, clear cell, and pleomorphic patterns, were seen frequently in late recurrences and often raised differential diagnostic problems with "nongerm cell" carcinomas. A smaller number of late recurrences consisted of other types of neoplasms. Twenty percent of patients with late recurrence had a nonteratomatous germ cell tumor other than yolk sac tumor, either alone, with yolk sac tumor, or with a "nongerm cell malignant tumor." Most of these nonteratomatous germ cell tumors other than yolk sac tumor were embryonal carcinoma, although rarely seminoma and choriocarcinoma were encountered. "Nongerm cell malignant tumors," including both sarcomas and carcinomas of various types, occurred in 23% of late-recurrence patients, either alone or with a nonteratomatous germ cell tumor. Late recurrences were seen in many different sites in these patients, including the retroperitoneum, abdomen, pelvis, liver, mediastinum, lung, bone (femur, vertebra, and rib), lymph nodes outside the retroperitoneum and mediastinum (supraclavicular, neck, and axillary regions), scrotum and inguinal regions, adrenal gland, chest wall, and buttocks. Follow-up data were available for 79 of the 91 patients studied. Duration of follow-up ranged from 2 months to 13 years after the patient's first late recurrences; the mean length of follow-up was 4.8 years. Patients whose late recurrences consisted of teratoma only had the most favorable outcomes, with 79% having no evidence of disease at last follow-up. Patients whose late recurrences consisted of pure "nongerm cell malignant tumor" or pure germ cell tumor (yolk sac tumor or other types) had a much worse prognosis: Only 36% to 37% were alive with no evidence of disease. Patients with two different types of nonteratomatous malignancies in their late recurrences had a dismal clinical course: Only 17% with both yolk sac tumor and other nonteratomatous germ cell tumor had no evidence of disease, whereas no patient with both nonteratomatous germ cell tumor and "nongerm cell malignant tumor" was disease free. Late recurrences consisting of teratoma alone often have a favorable outcome, but the prognosis in all other patients is poor. Furthermore, late recurrence is not likely to respond to chemotherapy and is best treated by surgical excision when possible.

Endodermal sinus tumor in children

Malignant germ cell tumors account for about 3% of neoplasms in children, and endodermal sinus tumor (EST) is the most common histological subtype. The authors reviewed 22 years' experience (at their institution) in the management of 37 patients with this tumor. Fifteen of them (41%) had a sacrococcygeal primary, 10 had a testicular tumor (27%), 6 had an ovarian tumor (16%), 3 had a vaginal tumor (8%) and 3 had tumors at other sites (8%). Seven (19%) patients presented with metastatic disease, primarily pulmonary. The serum alpha-fetoprotein (AFP) level was elevated in all cases tested. The initial chemotherapy regimen included vincristine, actinomycin, cyclophosphamide (VAC), and Adriamycin (6 patients), but since 1985 the regimen has been changed to include cisplatin or Carboplatin, etoposide, and bleomycin (21 patients). Eight patients with testicular tumors initially were treated with surgical excision alone. Computed tomography results were a poor predictor of recurrence, but AFP surveillance was extremely sensitive. No second-look operation detected residual tumor in the absence of AFP elevation. Initial relapse for all patients tended to occur early (within 2 years), locally, and often with pulmonary metastases. Although historically the prognosis for patients with EST has been poor, the overall 2-year survival rate in this series was 70%. The best prognosis was among the children who had a testicular primary tumor (survival rate, 100%). The 2-year survival rate for patients with ovarian tumors was 67%; for those with sacrococcygeal primaries it was 60%. These results suggest that the prognosis for children with EST has improved significantly over the past decade. Contributing factors include therapy based on cisplatin, etoposide, and bleomycin, and relapse surveillance with serial AFP determinations. Second-look procedures should be reserved for patients who have an increasing level of serum AFP, suspicious computed tomography findings, and no obvious evidence of metastatic disease.

Sacrococcygeal yolk sac carcinoma: imaging findings during treatment

Sacrococcygeal teratomas and their malignant counterparts (germ cell tumors) are the most common solid tumors in neonates. Prompt diagnosis is essential because the frequency of malignant transformation increases from 10-20 % in neonates to 67 % in patients over 2 months of age. Cross-sectional imaging has largely replaced surgical exploration for staging these tumors and assessing their response to chemotherapy. Radiologists must be familiar with changes in the imaging findings of these tumors during and after treatment so that they can advise clinicians regarding the efficacy of therapy and the presence or absence of recurrent disease. From our study, magnetic resonance imaging appears to be a better modality for assessing sacral invasion and metastases and distinguishing fibrotic masses from recurrent tumor.

A case of ovarian serous adenocarcinoma suggestive of transformation to an AFP-producing tumor during chemotherapy

Ovarian serous adenocarcinoma with AFP production is very rare. A case involving a 66-year-old woman with an elevated serum AFP level without detectable hepatic involvement. AFP-positive cells were seen in the tumor at the second surgery. Fifty-seven percent of serum AFP from the patient bound Con A, whereas 43% did not. Similarly, 54% of the tumor fluid also bound Con A. These suggest that the serum AFP was similar to that of gastrointestinal tumors and yolk-sac tumors.

Plasma protein and apolipoprotein synthesis by human yolk sac carcinoma cells in vitro

Three human yolk sac carcinoma cell lines were characterized for the expression of several markers. Each of the cell lines expressed alpha-fetoprotein, without detectable levels of chorionic gonadotropin, and the level of alpha-fetoprotein expression increased dramatically when the cultures were held without passage for extended periods. The secretion of a number of plasma proteins was documented by metabolic labeling, immunoprecipitation, and gel analysis. The major plasma proteins detected were alpha-1-antitrypsin, alpha-fetoprotein, transthyretin, beta-2 microglobulin, and plasminogen, with lower levels of transferrin and complement C4 released. Apolipoproteins B, E, and A1 were secreted in high levels as well and were found in the form of lipoprotein particles. Time course experiments on the synthesis of apolipoproteins E and A1 indicated that, as with alpha-fetoprotein, the level of synthesis increased substantially when the cultures were held without passage. The results indicate that these yolk sac carcinoma cells display a protein expression profile similar to that observed for the human yolk sac, and the possibility that the cells may have the potential to differentiate is discussed.

Laminin in testicular germ cell tumours. An immunohistochemical study

Thirty-five testicular germ cell tumours comprising 16 yolk sac tumours, 15 embryonal carcinomas and 13 seminomas were examined for the presence and distribution of laminin using an indirect immunoperoxidase technique. In addition, nine normal yolk sacs and 23 carcinomas of the lung were studied. All the yolk sac tumours were positively stained for laminin. Both extra- and intracellular staining were found. Hyaline, eosinophilic material present within the tumours was positively stained, although with varying intensity. In 12 out of 15 embryonal carcinomas, laminin was found as a membrane staining but cytoplasmic staining also occurred. In 10 out of 13 classical seminomas, a membrane staining of many tumour cells was found, while cytoplasmic staining occurred in only a few seminomas. In all but one of the yolk sacs, laminin was present in the membrane beneath both the mesoblastic outer cell layer and the visceral endoderm. Intracellular staining was seen in some of the cells in both cell layers. In nine out of 23 carcinomas of the lung, laminin occurred extra- as well as intracellularly. Thus, this study showed that in normal yolk sacs the presence of laminin was not found to be particularly associated with any of the cell layers. Likewise, demonstration of laminin within yolk sac tumours did not define different patterns or subtypes of the yolk sac tumour. In addition, demonstration of laminin was not found to be useful in differentiating either between yolk sac tumours and embryonal carcinomas or between seminomas and non-seminomatous germ cell tumours. The findings add, however, interesting knowledge to histogenesis and embryogenesis.

Electron microscopy of large cell undifferentiated and giant cell tumors

Electron microscopy is a valuable morphologic method for the diagnostic evaluation of undifferentiated tumors composed of polygonal or oval large cells and mononuclear or multinucleated giant cells. Although few ultrastructural details are pathognomonic, electron microscopic findings may add significantly to the formulation of the final diagnosis if used in the context of other pathomorphologic and clinical data. Contributions of electron microscopy to tumor diagnosis are summarized and illustrated with appropriate examples from personal experience in a routine university hospital laboratory.

Detection of AFP and HCG in metastatic testicular cancer after treatment with chemotherapy or radiation therapy

We used an indirect immunoperoxidase technique to detect alpha-fetoprotein (AFP) and human chorionic gonadotropin (HCG) in tissue sections of nine metastatic germ cell tumors excised after treatment with chemotherapy or radiation therapy, and correlated the results with the serum levels of AFP and HCG. In all but 1 case yolk sac tumor (YST) was the only histologic type that reacted for AFP (AFP+) and syncytiotrophoblasts (STB) were the only histologic type that reacted for HCG (HCG+). Among 5 cases with normalization of the serum AFP before surgery, 3 were associated with YST-/AFP-, 1 with YST+/AFP+, and 1 with YST+/AFP- metastases; and among 4 cases with normalization of the serum HCG all were associated with STB-/HCG- metastases. Among 3 cases with persistent elevation of the serum AFP, 1 was associated with YST+/AFP+, 1 with YST+/AFP-, and 1 with YST-/AFP- metastases; and of 2 cases with persistent elevation of the serum HCG, 1 was associated with STB-/HCG- and 1 with STB+/HCG+ metastases. These data suggest that marker normalization in the face of persistent tumor results primarily from eradication of YST and STB, but also from treatment-induced inhibition of AFP and HCG synthesis or secretion.

Experimental rat model for human yolk sac tumor

The morphological and biological characteristics of experimentally induced rat yolk sac carcinomas (ysca) are compared to those of human yolk sac tumors. It is shown that the rat ysca shares many morphological and biological properties with its human counterpart although the cellular origin is probably different. Whereas the human yolk sac tumors are believed to be of germ cell origin, the rat visceral yolk sac-derived tumors are not. The hypothesis is formulated that the rat ysca are derived from multipotential cells different from germ cells, and which originate in the extra-embryonic membrane after displacement.

Poorly differentiated (small cell) carcinoma of the ovary in young women: evidence supporting a germ cell origin

The clinical and pathologic features, including immunohistochemistry and electron microscopy, of six cases of poorly differentiated carcinoma of the ovary (small cell carcinoma) are presented. These tumors occurred in six young patients ranging in age from 10 to 24 years. Two patients had hypercalcemia. All tumors were unilateral, and four patients had advanced stage disease at presentation. Histologic features included sheets, nests, and cords of cells in a fibrous stroma, focal microcysts, and a dimorphic population of small and large cells. Eosinophilic, hyaline globules occurred in five cases, intercellular basement membrane-like substance in two cases, and glycogen in all cases. Five of six cases stained strongly for cytokeratin and vimentin; intracytoplasmic laminin was identified in three cases; and three cases were believed to show faint positivity for alpha-1-antitrypsin. Stains for alpha-fetoprotein were negative. Ultrastructural examination of two cases showed granular material in dilated rough endoplasmic reticulum, intermediate filaments, intracytoplasmic dense globules, maculae adherens, and extracellular basement membrane-like material. All of the cases proved rapidly fatal despite various therapies, as did a histologically similar testicular tumor that was admixed with seminoma and teratoma. We interpret these findings to indicate that this ovarian cancer is most likely of germ cell origin, and it may be related to yolk sac tumor, although it is clearly distinct from the classical yolk sac tumor.

Cytoskeleton of human embryonal carcinoma cells

Monoclonal antibodies to cytoskeletal proteins were used to study the intermediate filament proteins of human embryonal carcinoma (EC) cell lines, tumors produced in nude mice from these cell lines, and surgically removed testicular germ cell tumors. It was found that all cells of tumor lines 2102Ep, 1156 and Tera 1 react with antibodies to low molecular weight keratin proteins. By immunoblotting of SDS gels it was found that these lines expressed three keratin polypeptides (40K, 45K and 52K). Clonal line NTera-2 derived from Tera-2 differed from the above listed cell lines in that only 10% of the cells expressed the 40K keratin polypeptide. Upon treatment with retinoic acid 70% of NTera-2 cells became reactive with the antibody to the 40K keratin polypeptide. All cell lines contained a small population of vimentin-positive cells. The number of vimentin-positive cells could be increased by retinoic acid treatment of NTera-2 cells or by seeding the 2102Ep cells at low cell density. Neurofilament-positive cells could be induced in the cell line NTera-2 by retinoic acid treatment. Tumors produced from NTera-2 cells injected into nude mice contained cells reacting with antibodies to keratin, vimentin, neurofilament proteins and desmin. Keratin polypeptides were immunohistochemically demonstrated in embryonal carcinoma, yolk sac carcinoma and trophoblastic components of solid human germ cell tumors. Atypical intratubular cells ('carcinoma in situ') also reacted with antibodies to keratin.