Poorly Differentiated Nonkeratinizing Squamous Cell Carcinoma of the Thymus: Clinicopathologic and Molecular Genetic Study of 25 Cases

Molecular and Functional Key Features and Oncogenic Drivers in Thymic Carcinomas

Thymic epithelial tumors, comprising thymic carcinomas and thymomas, are rare neoplasms. They differ in histology, prognosis, and association with autoimmune diseases such as myasthenia gravis. Thymomas, but not thymic carcinomas, often harbor GTF2I mutations. Mutations of CDKN2A, TP53, and CDKN2B are the most common thymic carcinomas. The acquisition of mutations in genes that control chromatin modifications and epigenetic regulation occurs in the advanced stages of thymic carcinomas. Anti-angiogenic drugs and immune checkpoint inhibitors targeting the PD-1/PD-L1 axis have shown promising results for the treatment of unresectable tumors. Since thymic carcinomas are frankly aggressive tumors, this report presents insights into their oncogenic drivers, categorized under the established hallmarks of cancer.

Combined Thymic Epithelial Neoplasms - a Review

Thymic epithelial neoplasms are the most common tumors of thymic origin but are overall rare in the general population. Their morphologic diversity, ranging from low grade to overtly malignant lesions, along with various histologic growth patterns make them a diagnostically challenging group of tumors. Very occasionally, thymomas and thymic carcinomas may develop in combination with other benign or malignant lesions of thymic origin, further complicating the diagnostic process. The focus of this review lies on the spectrum of thymic epithelial tumors that present with other thymic lesions in the same tumor mass, such as multilocular thymic cysts, neuroendocrine neoplasms, lymphomas, and germ cell tumors among others. Awareness of the existence of such unusual tumors may not only aid in their diagnosis but may also have implications for prognostic and therapeutic purposes.

Basaloid Squamous Cell Carcinomas of the Thymus With Prominent B-Cell Lymphoid Hyperplasia: A Clinicopathologic and Immunohistochemical Study of 10 Cases

Ten cases of basaloid squamous cell carcinomas of the thymus are presented. The patients are 6 women and 4 men ranging in ages between 51 and 72 years (average: 61.5 y), who presented with nonspecific symptoms of cough, dyspnea, and chest pain with no history of malignancy, myasthenia gravis, or other autoimmune disease. Surgical resection of the mediastinal masses via thoracotomy or sternotomy was performed in all patients. Grossly, the tumors varied in size from 2 to 8 cm, were light tan in color, solid and slightly hemorrhagic, and had infiltrative borders. Histologically, scanning magnification showed elongated interanastomosing ribbons of tumors cells embedded in a lymphoid stroma containing germinal centers. At higher magnification, the tumors cells were round to oval with moderate amounts of lightly eosinophilic cytoplasm, oval nuclei, moderate cellular atypia, and mitotic activity ranging from 3 to 5 mitotic figures per 10 HPFs. In 8 cases, the tumor invaded perithymic adipose tissue, in 1 case the tumor infiltrated pericardium, and in 1 case, the tumor involved the pleura. Immunohistochemical stains showed positive staining in the epithelial component for pancytokeratin, p63, keratin 5/6, and p40, while CD20 and CD79a characterized the lymphoid component. Clinical follow-up was obtained in 7 patients. Two patients died within 24 months and 5 patients remained alive between 12 and 60 months. The current cases highlight the unusual feature of B-cell lymphoid hyperplasia in these tumors and their potential aggressive behavior.

Clinicopathologic features, tumor immune microenvironment and genomic landscape of EBV-related and EBV-unrelated poorly differentiated nonkeratinizing squamous cell carcinoma of the thymus

OBJECTIVES

Knowledge regarding thymic EBV-related poorly differentiated nonkeratinizing squamous cell carcinoma (PDNKSCC), also known as lymphoepithelial carcinoma (LEC), is extremely limited due to its rarity.

MATERIALS AND METHODS

This multi-institutional study enrolled 85 patients with thymic PDNKSCC. DNA in situ hybridization was performed to evaluate the EBV status of all 85 cases. Immunohistochemistry and next generation sequencing were performed to compare the differences in the clinicopathological and molecular features between EBV-related and EBV-unrelated PDNKSCC. Tumor-infiltrating lymphocytes (TILs) were also analyzed by these methods.

RESULTS

The 85 cases were classified into 27 EBV-related PDNKSCCs (31.8 %) and 58 EBV-unrelated PDNKSCCs (68.2 %) according to the EBV status, and 35 Lymphoepithelioma pattern (LP) (41.2 %) and 50 desmoplastic pattern (DP) (58.8 %) according to the histological characteristics. Compared to the EBV-unrelated PDNKSCC, EBV-related PDNKSCC showed a younger patient predominance and more commonly displayed a LP subtype. Additionally, LP-type cases were divided into two groups: Group 1 (EBV-related, 20/85) and Group 2 (EBV-unrelated, 15/85); the DP-type cases were divided into Group 3 (EBV-unrelated, 43/85) and Group 4 (EBV-related, 7/85). The four Groups showed a significant association with patients' OS and PFS. EBV-related PDNKSCC had significantly higher PD-L1 + tumor cells (TCs) and PD-L1 + and CD8 + immune cells (ICs) than EBV-unrelated PDNKSCC. The tumor microenvironment immune type (TMIT) I (PDL1-Tumor+/CD8-High) was more common in EBV-related PDNKSCC, especially in Group 1(LP and EBV related) with more than 90 % cases belonged to TMIT I. Molecular analysis demonstrated that EBV-related PDNKSCC had a significantly higher tumour mutational burden and frequency of somatic mutations than EBV-unrelated cases.

CONCLUSIONS

EBV-related PDNKSCC, especially the Group 1, could be a candidate for immunotherapy and EBV positivity may provide an indication for the selection of targeted therapy due to their high tumour mutational burden.

Intrathyroid thymic carcinoma: clinicopathological features and whole exome sequencing analysis

Intrathyroid thymic carcinoma (ITC) is a rare malignant tumour. We present nine cases of ITC that were analysed by immunohistochemical staining, of which five were analysed using whole exome sequencing (WES). These cases included six women and three men with an age range of 31-66 years. The average postoperative follow-up term was 37.8 months (range, 7-95 months), and all patients survived well except for one case with lung metastasis. Microscopically, ITC showed solid islands of tumour cells separated by fibrous connective tissue containing lymphocytes and other inflammatory cells. Tumour cells strongly expressed Ckpan (AE1/AE3), P63, and CD117. And all cases but one were positive for CD5. The median value of Ki-67 was 32% (range 10-60%). We observed partial positivity of Syn and CgA in only one case. ITC shares morphological and immunohistochemical similarities with thymic squamous cell carcinoma. In situ hybridization of EBER showed negative results. All cases were microsatellite stable, and the tumour mutational burden of the 5 cases was all < 1 mutations/Mb. WES showed higher mutation rates for N4BP1 (2/5), and many genetic alterations were related to the NF-kB signalling pathway, which is crucial for insight into the molecular mechanisms of the occurrence and development of ITC.

Desmoplastic Adamantinoma-like Thymic Carcinoma: Clinicopathologic, Immunohistochemical, and Molecular Study of 5 Cases

Five cases of a heretofore unreported rare variant of thymic carcinoma characterized by a striking resemblance to adamantinoma of the mandible are described. The tumors occurred in 4 women and 1 man aged 58 to 76 years (mean: 67.8 y); they arose in the anterior mediastinum and measured from 5.3 to 12.0 cm in greatest diameter (mean: 8.9 cm). Presenting symptoms included chest pain, shortness of breath, and in 2 patients, pleural effusion. One tumor was asymptomatic and discovered incidentally. Histologically, the tumors were extensively desmoplastic, and the cellular proliferation was characterized by multiple islands of squamous epithelium with striking peripheral palisading of nuclei and central areas containing clear cells resembling a stellate reticulum. Areas of preexisting spindle cell thymoma were identified in 2 cases; these areas gradually merged with the higher-grade component of the lesion. Cystic changes were noted in 3 cases. Immunohistochemical studies in 3 cases showed the tumor cells were positive for cytokeratins, p40 and p63, and all showed a high proliferation rate (>50% nuclear positivity) with Ki-67. Next-generation sequencing was performed in 2 cases that showed amplification of the AKT1 gene (copy numbers 6 and 13). Clinical follow-up in 3 patients showed recurrence and metastasis after 1 and 2 years; 1 patient passed away 2 years after diagnosis due to the tumor. Desmoplastic adamantinoma-like thymic carcinoma represents an unusual histologic variant of thymic carcinoma that needs to be distinguished from metastases from similar tumors to the mediastinum.

Atypical thymomas with squamoid and spindle cell features: clinicopathologic, immunohistochemical and molecular genetic study of 120 cases with long-term follow-up

Thymomas are rare tumors characterized by a broad range of morphologic appearances that can sometimes give rise to difficulties for classification. We have studied a series of 120 thymoma patients in whom the tumors were characterized by sheets of atypical epithelial cells with squamoid and/or spindle cell features. They occurred in 63 men and 57 women and presented as a discrete mass in the anterior mediastinum measuring 2-23 cm (mean: 8.2 cm). Patients' ages ranged from 14 to 86 years (mean: 57.8) and most had symptoms referable to a mass lesion. 20 patients had myasthenia gravis or other autoimmune disorder. 76 cases were characterized by a predominant population of round to polygonal tumor cells while 32 cases were characterized by atypical oval or spindle cells. 12 cases showed mixed features and 16 cases showed the development of thymic carcinoma arising from thymoma. All cases were positive for p40/p63 and cytokeratin AE1/AE3. 23 cases were positive for CD5 (25%), and 13 for CD117 (14%). MIB1 showed a significant increase in proliferative activity (mean = 11.6%). Next generation sequencing in 47 cases did not disclose any variants amenable to current targeted therapies. Clinical follow up ranging from 2 to 29 years showed a progressive increase in aggressive behavior and fatality rate with advancing stage. Overall survival was 87% at 5 years, 67% at 10 years, and 23% at 20 years. Completeness of resection and staging were the most significant parameters for survival. The more aggressive tumors followed a protracted clinical course with multiple recurrences and metastases over a long period of time (mean = 19.8 years from time of initial relapse to death). Atypical thymomas are a distinct category of thymic epithelial neoplasm characterized by a slowly progressive clinical course with increased potential for metastases, transformation to a higher-grade malignancy, and fatal outcome in some cases.

Thymic Lymphoepithelial Carcinoma Associated with Epstein-Barr Virus: Experiences and Literature Review

Thymic lymphoepithelial carcinoma (TLEC) is a primary thymic carcinoma that accounts for about 14% of all thymic epithelial tumors and is classified into 14 types. The histological morphology is similar to lymphoepithelioma, a type of undifferentiated nasopharyngeal carcinoma. It has been reported that squamous carcinoma accounts for approximately 80% of thymic carcinoma, followed by TLEC, which accounts for 6%. TLEC has been reported to be associated with Epstein-Barr virus (EBV), with EBV infection in TLEC tumor cells first noted by Lyvraz et al. in 1985. Tumors shown to be EBV-positive are classified as TLEC if lymphoplasmacytic infiltration is lacking. However, only about 50% of the cases are positive for EBV, which is lower compared to nasopharyngeal lymphoepithelioma. Instances of EBV infection in other types of thymic epithelial tumor have been reported at lower rates, which suggests that EBV infection may have an important influence on the carcinogenesis of TLEC, though the etiology is unknown. TLEC is a highly malignant tumor with poor prognosis, as affected patients have a median survival time of 22 months, according to 58 cases from the literature, while the 5-year survival rate is 34.4%. Presently, prognosis is not considered to be affected by the presence or absence of EBV positivity.

The incidence and prognosis of thymic squamous cell carcinoma: A Surveillance, Epidemiology, and End Results Program population-based study

BACKGROUND

Thymic carcinoma represents a rare type of malignant mediastinal tumor and has been the subject of controversy. Although independent prognostic factors related to thymic carcinoma have been investigated previously, few studies have focused specifically on the survival outcomes associated with thymic squamous cell carcinoma (TSCC). This study aims at presenting a survival analysis in this rare malignant disease at population level.

METHODS

We extracted the data of 216 patients with TSCC recorded from 1973 to 2015 from the Surveillance, Epidemiology, and End Results (SEER) database of the National Cancer Institute. The patients' demographic features, clinical traits, and treatment factors were analyzed in order to identify prognostic factors, which correlate overall survival using the Kaplan-Meier method as well as a multivariate Cox regression model, for TSCC.

RESULTS

The majority of patients were male, Caucasian, married, and insured. Furthermore, 58.3%, 54.6%, and 59.7% of patients TSCC underwent surgery, radiotherapy, and chemotherapy respectively. In a multivariate analysis, age of diagnosis (hazard ratio [HR]: 1.022, 95% confidence interval [CI]: 1.003-1.040, P = .020), surgical treatment (HR: 0.282, 95% CI: 0.164-0.484, P = .000), and stage (regional vs distant HR: 0.532, 95% CI: 0.324-0.872, P = .013; localized vs distant HR: 0.297, 95% CI: 0.133-0.664, P = .003) correlated with increased overall survival, whereas adjuvant therapy, including chemotherapy and radiotherapy, did not correlate with survival. Among surgically treated patients, age of diagnosis and stage were associated with better overall survival, while chemotherapy and radiotherapy did not contribute significantly to overall survival.

CONCLUSION

Surgery, age of diagnosis, and stage were associated with better overall survival among TSCC.

The role of needle core biopsies in the evaluation of thymic epithelial neoplasms

Thymic epithelial neoplasms are rare tumors derived from thymic epithelium that most often present as large anterior mediastinal masses. The vast majority of thymic epithelial neoplasms fall under the diagnostic category of thymoma, with a smaller percentage qualifying for a diagnosis of thymic carcinoma. The ability to render a definitive diagnosis on these tumors is generally hampered by their deep location and close proximity to vital structures, which makes biopsy sampling for histopathologic evaluation difficult. In recent years, the trend in medicine has been to opt for the least invasive procedure to obtain tissue samples that, by definition, implies also obtaining smaller and smaller biopsies, resulting in lesser amounts of tissue available for examination. In the mediastinum, the most common modalities for procuring biopsy samples from mass lesions include fine-needle aspiration, percutaneous core needle biopsy and video-assisted thoracoscopic biopsy. In this review, we will deal only with the role and limitations of percutaneous core biopsies in the interpretation of thymic epithelial neoplasms.

A multicenter analysis of genomic profiles and PD-L1 expression of primary lymphoepithelioma-like carcinoma of the lung

To understand the molecular mechanism of tumorigenesis of pulmonary lymphoepithelioma-like carcinoma and explore potential therapeutic strategies, we investigated the genomic profiles and PD-L1 expression of 29 Chinese pulmonary lymphoepithelioma-like carcinoma patients at various stages. We performed capture-based targeted sequencing on tissue samples collected from 27 patients with sufficient samples using a panel consisting of 520 cancer-related genes, spanning 1.64 Mb of the human genome. We identified 184 somatic mutations in 109 genes from 26 patients. One patient had no mutations detected by this panel. Copy number variations were detected in 52% (14/27) of the patients, with a majority having advanced-stage disease (10/14). Except for the detection of ERBB2 amplification and KRAS mutation in two patients, no other classic lung cancer driver mutations were detected. Interestingly, 78% (21/27) of the patients had mutations in epigenetic regulators. Of the 184 mutations identified, 51 occurred in 29 epigenetics-related genes. Furthermore, we performed PD-L1 immunohistochemistry staining using the Dako 22C3 assay and demonstrated that 69% (20/29) of the cohort had positive PD-L1 expression, of which three patients received and benefited from a PD-1 inhibitor. In conclusion, we elucidated a distinct genomic landscape associated with pulmonary lymphoepithelioma-like carcinoma with no classic lung cancer driver mutation but an enrichment of mutations in epigenetic regulators. The detection of high PD-L1 expression and lack of any canonical druggable driver mutations raises the potential of checkpoint immunotherapy for pulmonary lymphoepithelioma-like carcinoma.

Total thymectomy for thymic lymphoepithelioma-like carcinoma-report of two cases

Background

Thymic carcinoma has been classified into 12 subtypes, thymic lymphoepithelioma-like carcinoma (LELC) is a type of them, and has a pathological organization similar to that of lymphoepithelioma, an undifferentiated type of nasopharyngeal carcinoma. According to a report from the International Thymic Malignancy Interest Group (ITMIG), thymic LELC is a rare tumor and accounts for 6% of all thymic carcinoma cases. We report two cases of surgical resection for thymic LELC and perform a search of other reports of thymic LELC, and clinical manifestations and follow-up data thus obtained are summarized.

Case presentation

Two patients underwent surgical resection for thymic LELC. In both, tumors were detected in the anterior mediastinum and a total thymectomy was performed. Each was diagnosed with thymic LELC and classified in accordance with the Masaoka staging system as modified stage II. In recent examinations, one patient was doing well after undergoing total resection, whereas early recurrence of distant lymph node metastasis was noted in the other at 5 months after the total resection procedure and died thereafter from a different disease.

Conclusion

We report two cases of surgical resection for thymic LELC. A successful total resection may positively affect prognosis: thus, long-term follow-up examinations must be performed.