Primary extraskeletal osteosarcomas of the pleura: A clinicopathological, immunohistochemical, and molecular analysis of 4 cases.

Four primary extraskeletal osteosarcomas of the pleura are presented. The patients were men between the ages of 63 and 78 years (average: 70.5 years) who presented with symptoms of chest pain, cough, and shortness of breath. Diagnostic imaging showed variably calcified, pleural-based masses and/or diffuse pleural thickening, clinically mimicking mesothelioma. Thoracoscopic surgical material was obtained for histopathological diagnosis. Histological findings showed the presence of a neoplastic spindle cell proliferation composed of fusiform cells with scant cytoplasm, elongated nuclei and inconspicuous nucleoli. Mitotic activity was easily identified. Additionally, all tumors showed extensive osseous differentiation in the form of osteoid matrix production; one tumor demonstrated additional chondrosarcomatous elements and another showed focal myxoid changes. Immunohistochemical analysis revealed that the tumor cells were uniformly negative for a wide variety of antibodies, including keratin AE1/AE3, keratin 5/6, D2-40, EMA, calretinin, WT-1, BerEP4, and HEG1; BAP1 was retained in all cases. In addition, fluorescence in situ hybridization for CDKN2A (p16) was negative for homozygous deletion in all tumors. Clinical follow-up showed that one patient had died 8 months after diagnosis and one had remained alive with short post-diagnostic follow-up. The tumors herein described highlight a challenging issue in the separation of mesothelioma with heterologous elements from true osteosarcomas of pleural origin. We propose that a diagnosis of extraskeletal osteosarcoma of the pleura is rendered for tumors with malignant osseous and/or cartilaginous differentiation in which comprehensive immunohistochemical studies and FISH analysis have failed to provide support for a diagnosis of mesothelioma with heterologous elements.

Atypical Thymoma (WHO Type B3) with Prominent Microcystic and Mucoid Changes Mimicking Thymic Mucoepidermoid Carcinoma: A Clinicopathological and Immunohistochemical Study of Five Cases.

Five atypical thymomas (WHO type B3) with prominent microcystic and mucoid changes are presented. The patients were four men and one woman between the ages of 57 and 72 years. The patients presented with non-specific symptoms of cough, chest pain, and dyspnea. None of the patients had a history of myasthenia gravis. Diagnostic imaging revealed the presence of anterior mediastinal masses and surgical resection was accomplished in all patients. Macroscopically, the tumors ranged in size from 3.5 to 5.0 cm in greatest diameter; four of these were well circumscribed but unencapsuled, tan colored tumors without evidence of necrosis, hemorrhage, or gross cystic changes. One tumor had more infiltrative borders and was involving the mediastinal pleura. Microscopically, the low power view was characterized by prominent microcysts that were filled with a mucoid granular material. Higher magnification demonstrated a homogenous epithelial proliferation with mild cytologic atypia but lacking mitotic activity. Focal areas of squamoid differentiation were identified but perivascular spaces were absent. Histochemical staining confirmed mucinous material in the microcysts but no intracytoplasmic mucin. Immunohistochemical stains showed positive staining of the tumor cells with keratin AE1/AE3, keratin 5/6, p63, and p40. No terminal deoxynucleotidyl transferase+/CD3 + immature lymphocytes were identified. Clinical follow-up demonstrated that four patients have remained alive without recurrence while one patient was lost to follow-up. This report highlights histological features in atypical thymoma that may be confused with other tumors, especially thymic mucoepidermoid carcinoma. Separation of these tumors may be important for patient management and prognosis.

Integrative genomic and transcriptomic profiling of pulmonary sarcomatoid carcinoma identifies molecular subtypes associated with distinct immune features and clinical outcomes.

Background: Pulmonary sarcomatoid carcinoma (PSC) is a rare and aggressive subtype of non-small cell lung cancer (NSCLC), characterized by the presence of epithelial and sarcoma-like components. The molecular and immune landscape of PSC has not been well defined. Methods: Multiomics profiling of 21 pairs of PSCs with matched normal lung tissues was performed through targeted high-depth DNA panel, whole-exome, and RNA sequencing. We describe molecular and immune features that define subgroups of PSC with disparate genomic and immunogenic features as well as distinct clinical outcomes. Results: In total, 27 canonical cancer gene mutations were identified, with TP53 the most frequently mutated gene, followed by KRAS. Interestingly, most TP53 and KRAS mutations were earlier genomic events mapped to the trunks of the tumors, suggesting branching evolution in most PSC tumors. We identified two distinct molecular subtypes of PSC, driven primarily by immune infiltration and signaling. The Immune High (IM-H) subtype was associated with superior survival, highlighting the impact of immune infiltration on the biological and clinical features of localized PSCs. Conclusions: We provided detailed insight into the mutational landscape of PSC and identified two molecular subtypes associated with prognosis. IM-H tumors were associated with favorable recurrence-free survival and overall survival, highlighting the importance of tumor immune infiltration in the biological and clinical features of PSCs.

Thoracic solitary fibrous tumors with small cell features: A clinicopathological and immunohistochemical analysis of 5 cases.

Five cases of thoracic solitary fibrous tumor (SFT) with small cell features are presented mimicking a neuroendocrine neoplasm. The patients were four men and one woman aged 43 to 74 years who presented with symptoms of chest pain, cough, dyspnea or hemoptysis. Two tumors were intrapulmonary neoplasms, while three were pleural-based. Grossly, the tumors ranged in size from 4 to 6 cm and were white and solid; in two tumors necrosis was apparent. Histologically, they were characterized by a cellular proliferation composed of small cells with round nuclei and inconspicuous nucleoli. The cellular proliferation in some areas had a subtle nested pattern, while in other areas the tumor showed extensive sclerosis and small vessel proliferation. Cellular pleomorphism was not marked and the mitotic activity varied from 1 to 5 mitotic figures per 10 high power fields. Microscopically, necrosis was observed in two cases and focally present in one. Immunohistochemical stains showed tumors cells universally negative for pancytokeratin; in the two pulmonary cases, focal staining for synaptophysin, CD56, and INSM1 was observed. The unexpected lack of expression of pancytokeratin led to additional analysis revealing positive staining with CD34 and STAT6 confirming a diagnosis of SFT. Clinical follow-up showed tumor recurrence in one patient while three patients remained alive and well after a period of 12 to 20 months. The current cases highlight an unusual variant of SFT that may be confused with other small cell tumor entities, such as neuroendocrine or neuroectodermal tumors, especially when originating in the thoracic cavity.

Primary thymic adenoid cystic carcinoma with high-grade transformation: A clinicopathological and immunohistochemical analysis of 4 cases.

Four cases of a distinct carcinoma of the thymic gland are presented. The patients were 4 adult males with an age range from 40 to 47 years (mean, 43.5 years). Clinically, all patients presented with non-specific respiratory symptoms. None of the patients had any prior history of head and neck neoplasm or surgery in that anatomic area. Large anterior mediastinal masses were found on diagnostic imaging with concurrent metastatic disease to pleura, lungs, regional lymph nodes and bones. Microscopically, all tumors were composed of a solid proliferation of hyperchromatic, monomorphic small cells with focal cytoplasmic clearing embedded in a fibromyxoid stroma. In one case, occasional duct-like structures were identified. Immunohistochemically, the tumors were positive for pancytokeratin, CD117 and MYB and negative for myoepithelial markers. Systemic chemotherapy was initiated in all patients. Despite therapy, clinical follow-up revealed that all 4 patients died of their disease 11-23 months after their initial diagnosis. The cases in this series highlight a tumor that is different from conventional thymic carcinoma and that has the morphological and immunohistochemical features commonly seen in adenoid cystic carcinomas with high-grade transformation. Correct diagnosis is essential for patient management.

Pathology of Surgically Resected Lung Cancers Following Neoadjuvant Therapy.

In around 30% of patients, non-small cell lung cancer is diagnosed at an advanced but resectable stage. Adding systemic therapy has shown clear benefit over surgery alone in locally advanced disease, and currently, chemo-immunotherapy in the adjuvant or neoadjuvant setting is the new standard for patients without targetable mutations. One major advantage of the neoadjuvant approach is the possibility of an immediate evaluation of the treatment effect, highlighting the role of pathology as an important contributor at the forefront of clinical decision-making and research. This review provides a summary and an update on current guidelines for histological evaluation of treatment effect after neoadjuvant therapy, also known as regression grading, and discusses newer data focusing on areas of evolving questions and controversies, such as the gross examination of the tumor and tumor bed, weighted versus unweighted evaluation approaches, discussion of histologic tumor type-specific cut-offs for major pathologic response, assessment of lymph nodes and regression grading after immunotherapy and targeted therapy. As no data or recommendations exist on regression grading of multiple tumor nodules, a practical approach is recommended. Lastly, we will touch on additional tissue biomarkers and summarize recent advances in the ardently discussed field of using circulating tumor DNA for the evaluation of treatment response.

Pathologic Processing of Lung Cancer Resection Specimens After Neoadjuvant Therapy.

Neoadjuvant treatment of non-small cell lung cancer challenges the traditional processing of pathology specimens. Induction therapy before resection allows evaluation of the efficacy of neoadjuvant agents at the time of surgery. Many clinical trials use pathologic tumor response, measured as major pathologic response (MPR, ≤10% residual viable tumor [RVT]) or complete pathologic response (CPR, 0% RVT) as a surrogate of clinical efficacy. Consequently, accurate pathologic evaluation of RVT is crucial. However, pathologic assessment has not been uniform, which is particularly true for sampling of the primary tumor, which instead of the traditional processing, requires different tissue submission because the focus has shifted from tumor typing alone to RVT scoring. Using a simulation study, we analyzed the accuracy rates of %RVT, MPR, and CPR of 31 pretreated primary lung tumors using traditional grossing compared with the gold standard of submitting the entire residual primary tumor and identified the minimum number of tumor sections to be submitted to ensure the most accurate scoring of %RVT, MPR, and CPR. Accurate %RVT, MPR, and CPR calls were achieved in 52%, 87%, and 81% of cases, respectively, using the traditional grossing method. Accuracy rates of at least 90% for these parameters require either submission of all residual primary tumor or at least 20 tumor sections. Accurate %RVT, MPR, and CPR scores cannot be achieved with traditional tumor grossing. Submission of the entire primary tumor, up to a maximum of 20 sections, is required for the most accurate reads.

Surgical outcomes after chemotherapy plus nivolumab and chemotherapy plus nivolumab and ipilimumab in patients with non-small cell lung cancer.

OBJECTIVE: Chemotherapy plus nivolumab is the standard of care neoadjuvant treatment for patients with resectable stage IB to IIIA non-small cell lung cancer. The influence of dual checkpoint blockade with chemotherapy on surgical outcomes remains unknown. We aimed to determine operative complexity and perioperative outcomes associated with neoadjuvant chemotherapy and nivolumab with or without ipilimumab. METHODS: A total of 44 patients with stage IB (≥4 cm) to IIIA non-small cell lung cancer were treated on sequential platform arms of the NEOSTAR trial. A total of 22 patients were treated with nivolumab + chemotherapy, and 22 patients were treated with ipilimumab + nivolumab + chemotherapy. The safety of surgical resection after neoadjuvant therapy was estimated using 30-day complication rates. Operative reports and surgeons' narratives were evaluated to determine procedural complexity and operative conduct. RESULTS: All 22 of 22 patients (100%) treated with nivolumab + chemotherapy underwent surgical resection: 20 R0 (90.9%), 17 (77.3%) lobectomies, 1 wedge resection, 2 segmentectomies, and 2 pneumonectomies. The majority, 21 of 22 (95%), were performed by thoracotomy. A total of 13 of 22 (59.1%) were rated as challenging resections. A total of 4 of 22 patients (18.2%) experienced grade 3 or greater Clavien-Dindo complication. A total of 20 of 22 patients (90.9%) treated with ipilimumab + nivolumab + chemotherapy underwent surgical resection: 19 R0 (95%), 18 (90%) lobectomies, 1 pneumonectomy, and 1 segmentectomy. A total of 16 of 20 (80%) resections were performed via thoracotomy, 3 of 20 (15%) via robotics, and 1 of 20 (5%) via thoracoscopy. A total of 9 of 20 (45%) resections were considered challenging. A total of 4 of 20 patients (20%) experienced grade 3 or greater Clavien-Dindo complication. CONCLUSIONS: Surgical resections are feasible and safe, with high rates of R0 after neoadjuvant chemotherapy and nivolumab with or without ipilimumab. Overall, approximately half of cases (22/42, 52.3%) were considered to be more challenging than a standard lobectomy.

Neurogenic tumours of the posterior mediastinum and differential diagnosis considerations.

The mediastinal compartment harbours vital organs and structures, including the heart, great vessels, major airways, and thymus. These structures are embedded in and associated with soft-tissue elements consisting of adipose and fibro-collagenous tissue in which soft-tissue tumours may develop. A detailed inventory of soft-tissue tumours that may be encountered in the mediastinum based on the WHO 2013 classification was published in 2015. In addition, several comprehensive reviews on mediastinal soft-tissue pathology are available, including reviews focusing specifically on a single tumour type. This review will focus on primary neurogenic and spindle cell tumours of the somatic soft tissue of the posterior mediastinum and provide a discussion of the pertinent differential diagnoses.

Spindle cell thymoma and its histological mimickers.

Spindle cell thymomas are the most common spindle cell neoplasms of the anterior mediastinum. These tumors belong to the group of thymic epithelial neoplasms and are known for their wide histomorphologic spectrum. This histological heterogeneity is the reason why unequivocal diagnosis can be challenging, especially when dealing with small biopsy material. Conversely, less conventional patterns of the tumor may also pose significant diagnostic problems in resected material and the differential diagnosis often includes other spindle cell neoplasms that are known to arise in the mediastinal cavity. These can be of variable origin and may share overlapping pathological features with spindle cell thymoma. Since spindle cell thymomas are tumors that primarily affect the adult population and predominantly arise from the thymic gland in the anterior mediastinum, this review will focus on the differential diagnosis with other spindle cell neoplasms that share similar demographic characteristics and, for the most part, originate from the anterior mediastinal compartment. These include other epithelial spindle cell tumors of thymic origin (sarcomatoid thymic carcinoma and spindle cell carcinoid tumor), mesenchymal neoplasms [solitary fibrous tumor (SFT), synovial sarcoma, and dedifferentiated liposarcoma] and various other tumors with spindle cell morphology, that may occasionally involve the anterior mediastinum. The clinical, pathological, immunohistochemical and molecular hallmarks of these lesions will be discussed and useful tips for the differential diagnosis with spindle cell thymoma will be provided.

International Association for the Study of Lung Cancer Study of Reproducibility in Assessment of Pathologic Response in Resected Lung Cancers After Neoadjuvant Therapy.

INTRODUCTION: Pathologic response has been proposed as an early clinical trial end point of survival after neoadjuvant treatment in clinical trials of NSCLC. The International Association for the Study of Lung Cancer (IASLC) published recommendations for pathologic evaluation of resected lung cancers after neoadjuvant therapy. The aim of this study was to assess pathologic response interobserver reproducibility using IASLC criteria. METHODS: An international panel of 11 pulmonary pathologists reviewed hematoxylin and eosin-stained slides from the lung tumors of resected NSCLC from 84 patients who received neoadjuvant immune checkpoint inhibitors in six clinical trials. Pathologic response was assessed for percent viable tumor, necrosis, and stroma. For each slide, tumor bed area was measured microscopically, and pre-embedded formulas calculated unweighted and weighted major pathologic response (MPR) averages to reflect variable tumor bed proportion. RESULTS: Unanimous agreement among pathologists for MPR was observed in 68 patients (81%), and inter-rater agreement (IRA) was 0.84 (95% confidence interval [CI]: 0.76-0.92) and 0.86 (95% CI: 0.79-0.93) for unweighted and weighted averages, respectively. Overall, unweighted and weighted methods did not reveal significant differences in the classification of MPR. The highest concordance by both methods was observed for cases with more than 95% viable tumor (IRA = 0.98, 95% CI: 0.96-1) and 0% viable tumor (IRA = 0.94, 95% CI: 0.89-0.98). The most common reasons for discrepancies included interpretations of tumor bed, presence of prominent stromal inflammation, distinction between reactive and neoplastic pneumocytes, and assessment of invasive mucinous adenocarcinoma. CONCLUSIONS: Our study revealed excellent reliability in cases with no residual viable tumor and good reliability for MPR with the IASLC recommended less than or equal to 10% cutoff for viable tumor after neoadjuvant therapy.

PAX5 and CD70 are expressed in thymic carcinoma but not in atypical thymoma (WHO type B3 thymoma): an immunohistochemical analysis of 60 cases.

AIMS: Thymic carcinoma and atypical thymoma (WHO type B3 thymoma) are unusual tumours the separation of which may be challenging in small biopsies. Both tumours consist of epithelioid tumour cells that share similar morphology and immunophenotype with conventional markers. Therefore, additional antibodies are needed to differentiate between these tumours. METHODS: For this purpose, a panel of immunohistochemical stains including PAX2, PAX5, PAX8 (all monoclonal) and CD70 was used on whole tumour sections of 30 thymic carcinomas and 30 atypical thymomas to determine the expression pattern of these antibodies. In addition, all tumours were stained with markers that are well known to be expressed in both tumours, including pancytokeratin and cytokeratin 5/6. The percentage of positive tumour cells as well as the intensity of staining were evaluated and scored. RESULTS: PAX5 stained close to 70% of thymic carcinomas while all atypical thymomas were negative for this marker. CD70 was expressed in 18 thymic carcinomas (60%) and in 1 case of atypical thymoma (3%). On the other hand, monoclonal PAX8 was negative in all cases while PAX2 was positive in a single thymic carcinoma. Of the established stains, pancytokeratin and cytokeratin 5/6 were equally positive in both tumours. CONCLUSIONS: Among the markers explored, only PAX5 and CD70 appear to be differentially expressed and are predominantly restricted to thymic carcinomas. Therefore, in small biopsy specimens and in resections in which the morphological features remain equivocal, application of these particular stains may facilitate separation of thymic carcinoma and atypical thymoma.

Radiographic response to neoadjuvant therapy in pleural mesothelioma should serve as a guide for patient selection for cytoreductive operations.

Background: Malignant pleural mesothelioma (MPM) is associated with poor prognosis despite advances in multimodal therapeutic strategies. While patients with resectable disease may benefit from added survival with oncologic resection, patient selection for mesothelioma operations often relies on both objective and subjective evaluation metrics. We sought to evaluate factors associated with improved overall survival (OS) in patients with mesothelioma who underwent macroscopic complete resection (MCR). Methods: Patients with MPM who received neoadjuvant therapy and underwent MCR were identified in a prospectively maintained departmental database. Clinicopathologic, blood-based, and radiographic variables were collected and included in a Cox regression analysis (CRA). Response to neoadjuvant therapy was characterized by a change in tumor thickness from pretherapy to preoperative scans using the modified RECIST criteria. Results: In this study, 99 patients met the inclusion criteria. The median age of the included patients was 64.7 years, who were predominantly men, had smoking and asbestos exposure, and who received neoadjuvant therapy. The median change in tumor thickness following neoadjuvant therapy was -16.5% (interquartile range of -49.7% to +14.2%). CRA demonstrated reduced OS associated with non-epithelioid histology [hazard ratio (HR): 3.06, 95% confidence interval (CI): 1.62-5.78, p < 0.001] and a response to neoadjuvant therapy inferior to the median (HR: 2.70, CI: 1.55-4.72, p < 0.001). Patients who responded poorly (below median) to neoadjuvant therapy had lower median survival (15.8 months compared to 38.2 months, p < 0.001). Conclusion: Poor response to neoadjuvant therapy in patients with MPM is associated with poor outcomes even following maximum surgical cytoreduction and should warrant a patient-centered discussion regarding goals of care and may therefore help guide further therapeutic decisions.

Non-Neoplastic Thoracic Cysts: A Clinicopathologic Study of 136 Cases.

Benign cysts of the thoracic cavity represent a group of rare lesions, the spectrum of which is expanding. Most of these are congenital in nature, secondary to abnormal development during embryogenesis while a smaller subset represents acquired lesions. We retrospectively reviewed the clinicopathologic features of 136 patients with thoracic cysts that were treated in our institution over a span of 20 years. The patients were 85 female and 51 male patients with an average age of 51 years. Eighty-four of the patients were asymptomatic (62%), the remainder mainly presented with chest pain, shortness of breath, or cough. Surgical resection was performed in 123 patients while 12 patients were treated with aspiration only and 1 underwent core biopsy. The cyst size ranged from 0.5 to 14.8 cm (mean, 4.4 cm); histologically, the lesions included 50 thymic cysts (28 multilocular; 22 unilocular), 37 bronchogenic cysts, 23 pleuropericardial cysts, 12 unclassified cysts, 6 Müllerian cysts, 5 enteric cysts, and 3 parathyroid cysts. Clinical follow-up revealed that 97 patients were alive and well 4 months to 37 years after initial diagnosis; 25 patients were lost to follow-up and 14 patients died of unrelated causes. The current study is one of the largest studies on the subject with emphasis on clinicopathologic characteristics. This series has a higher incidence of thymic cysts compared with prior publications and covers a wider spectrum of different histologic types than previously reported.

Primary epithelioid hemangioendotheliomas and angiosarcomas of the pleura: a clinicopathological and immunohistochemical analysis of 13 cases.

Thirteen cases of primary epithelioid hemangioendotheliomas (EHE) and epithelioid angiosarcomas (EA) of the pleura are presented. The patients were 7 men and 6 women between the ages of 34 and 65 years (mean: 47 years). The patients presented with non-specific symptoms of cough, dyspnea, and chest pain. Diagnostic imaging revealed the presence of either diffuse pleural thickening or pleural nodules involving the serosal surfaces. Open surgical biopsies were obtained in all cases. Histologically, eight tumors were characterized by the presence of a cellular proliferation composed of medium-sized epithelioid cells embedded in a myxohyaline stroma and a variable spindle cell component. Cellular atypia was mild to moderate and mitotic activity ranged from 1 to 2 per 2 mm2. Immunohistochemical stains for vascular markers, including CAMTA1 were positive, confirming a diagnosis of EHE. Five cases of epithelioid angiosarcomas were characterized by a neoplastic cellular proliferation admixed with areas of necrosis and hemorrhage and characterized by medium-sized epithelioid to spindle-shaped cells with eosinophilic cytoplasm, round to oval nuclei and prominent nucleoli. In addition, marked cytologic atypia and a mitotic activity ranging from 3 to 5 per 2 mm2 were identified. Immunohistochemical studies demonstrated positive staining for vascular markers; however, CAMTA1 was negative. Clinical follow-up obtained in eleven cases showed that all patients had died within 30 months post diagnosis. The current study highlights that even though it may be important to histologically separate EHE from EA for academic purposes, primary pleural origin of these tumors appears to portent an aggressive clinical behavior.

Chromophobe-like carcinoma of the thymus: A clinicopathological and immunohistochemical correlation of 5 cases.

Five cases of primary thymic carcinoma with distinct histopathological features resembling chromophobe carcinomas are presented. The patients were four men and one woman ranging in age between 43 and 72 years. Clinically, the patients presented with non-specific symptoms of dyspnea and chest pain. Diagnostic imaging revealed the presence of anterior mediastinal masses. All patients underwent complete surgical resection of their tumors via thoracotomy. Grossly, the tumors measured between 4.0 and 5.5 cm in greatest diameter and were ill-defined neoplasms with infiltrative borders; they were light brown in color and had a lobulated surface. Areas of hemorrhage and necrosis were not identified. Histologically, all tumors shared similar histopathological features, mainly the presence of infiltrative tumor islands separated by a fibrocollagenous stroma. At higher magnification, the neoplastic cellular proliferation was composed of medium-sized, round to polygonal cells with eosinophilic or granular cytoplasm and a clear perinuclear cytoplasmic halo, which imparted a chromophobe-like appearance. Nuclear atypia and mitotic activity were identified. Histochemical stains for colloidal iron were negative while immunohistochemical stains for pancytokeratin, cytokeratin 5/6, and p40 were positive in all cases, supporting squamous differentiation in these tumors. Clinical follow-up information was obtained in three patients all of whom died between 3 and 5 years after initial diagnosis, while two patients were lost to follow-up. The cellular characteristics of these tumors represent an unusual variant of thymic carcinoma that may pose a diagnostic challenge in small biopsies and that could be easily confused with other primary or metastatic tumors.

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.

Atypical thymoma (epithelial-rich thymoma, well-differentiated thymic carcinoma, WHO type B3 thymoma): A conundrum.

Thymomas composed predominantly of epithelioid tumor cells with scattered lymphocytes have been well recognized in the literature. This subtype of thymoma has been variously termed epithelial-rich thymoma, well-differentiated thymic carcinoma, atypical thymoma, or World Health Organization (WHO) type B3 thymoma. Regardless of the designation however, these tumors are known to show a spectrum of histopathological growth patterns that may pose challenges in interpretation and diagnosis, particularly when dealing with small mediastinoscopic biopsies. Just like any other type of thymoma, those composed predominantly of epithelioid cells may present as encapsulated or invasive tumors. Nevertheless, compared to other subtypes of thymoma, they are uncommon neoplasms. Therefore, it becomes very important to sufficiently sample thymomas before making a diagnosis of a particular subtype, especially when the tumor is rich in epithelioid cells and only has a scant lymphocytic component. Because of the unusual occurrence of these tumors, there are only few large series of cases that attempt to highlight not only the more salient histopathological features but also the most important immunohistochemical and molecular characteristics.

Neoadjuvant chemotherapy plus nivolumab with or without ipilimumab in operable non-small cell lung cancer: the phase 2 platform NEOSTAR trial.

Neoadjuvant ipilimumab + nivolumab (Ipi+Nivo) and nivolumab + chemotherapy (Nivo+CT) induce greater pathologic response rates than CT alone in patients with operable non-small cell lung cancer (NSCLC). The impact of adding ipilimumab to neoadjuvant Nivo+CT is unknown. Here we report the results and correlates of two arms of the phase 2 platform NEOSTAR trial testing neoadjuvant Nivo+CT and Ipi+Nivo+CT with major pathologic response (MPR) as the primary endpoint. MPR rates were 32.1% (7/22, 80% confidence interval (CI) 18.7-43.1%) in the Nivo+CT arm and 50% (11/22, 80% CI 34.6-61.1%) in the Ipi+Nivo+CT arm; the primary endpoint was met in both arms. In patients without known tumor EGFR/ALK alterations, MPR rates were 41.2% (7/17) and 62.5% (10/16) in the Nivo+CT and Ipi+Nivo+CT groups, respectively. No new safety signals were observed in either arm. Single-cell sequencing and multi-platform immune profiling (exploratory endpoints) underscored immune cell populations and phenotypes, including effector memory CD8+ T, B and myeloid cells and markers of tertiary lymphoid structures, that were preferentially increased in the Ipi+Nivo+CT cohort. Baseline fecal microbiota in patients with MPR were enriched with beneficial taxa, such as Akkermansia, and displayed reduced abundance of pro-inflammatory and pathogenic microbes. Neoadjuvant Ipi+Nivo+CT enhances pathologic responses and warrants further study in operable NSCLC. (ClinicalTrials.gov registration: NCT03158129 .).