Maackia amurensis seed lectin (MASL) and soluble human podoplanin (shPDPN) sequence analysis and effects on human oral squamous cell carcinoma (OSCC) cell migration and viability.

Maackia amurensis lectins serve as research and botanical agents that bind to sialic residues on proteins. For example, M. amurensis seed lectin (MASL) targets the sialic acid modified podoplanin (PDPN) receptor to suppress arthritic chondrocyte inflammation, and inhibit tumor cell growth and motility. However, M. amurensis lectin nomenclature and composition are not clearly defined. Here, we sought to definitively characterize MASL and its effects on tumor cell behavior. We utilized SDS-PAGE and LC-MS/MS to find that M. amurensis lectins can be divided into two groups. MASL is a member of one group which is composed of subunits that form dimers, evidently mediated by a cysteine residue in the carboxy region of the protein. In contrast to MASL, members of the other group do not dimerize under nonreducing conditions. These data also indicate that MASL is composed of 4 isoforms with an identical amino acid sequence, but unique glycosylation sites. We also produced a novel recombinant soluble human PDPN receptor (shPDPN) with 17 threonine residues glycosylated with sialic acid moieties with potential to act as a ligand trap that inhibits OSCC cell growth and motility. In addition, we report here that MASL targets PDPN with very strong binding kinetics in the nanomolar range. Moreover, we confirm that MASL can inhibit the growth and motility of human oral squamous cell carcinoma (OSCC) cells that express the PDPN receptor. Taken together, these data characterize M. amurensis lectins into two major groups based on their intrinsic properties, clarify the composition of MASL and its subunit isoform sequence and glycosylation sites, define sialic acid modifications on the PDPN receptor and its ability to act as a ligand trap, quantitate MASL binding to PDPN with KD in the nanomolar range, and verify the ability of MASL to serve as a potential anticancer agent.

CHRNA6 RNA In Situ Hybridization Is a Useful Tool for the Diagnosis of Extraskeletal Myxoid Chondrosarcoma.

Extraskeletal myxoid chondrosarcoma (EMC) is an uncommon mesenchymal neoplasm characteristically composed of uniform-appearing round to spindle-shaped cells with eosinophilic cytoplasm and abundant myxoid extracellular matrix. Although the majority of cases harbor a pathognomonic t(9;22) translocation that fuses EWSR1 with the orphan nuclear receptor NR4A3, there are less common variants that partner NR4A3 with TAF15, TCF12, or TFG. By immunohistochemistry, EMC has features of both cartilaginous and neuroendocrine differentiation, as evidenced by inconsistent expression of S100 protein and synaptophysin or INSM1, respectively, in a subset of cases. Given the limitations of available immunohistochemical stains for the diagnosis of EMC, we analyzed genome-wide gene expression microarray data to identify candidate biomarkers based on differential expression in EMC in comparison with other mesenchymal neoplasms. This analysis pointed to CHRNA6 as the gene with the highest relative expression in EMC (96-fold; P = 8.2 × 10-26) and the only gene with >50-fold increased expression in EMC compared with other tumors. Using RNA chromogenic in situ hybridization, we observed strong and diffuse expression of CHRNA6 in 25 cases of EMC, including both EWSR1-rearranged and TAF15-rearranged variants. All examined cases of histologic mimics were negative for CHRNA6 overexpression; however, limited CHRNA6 expression, not reaching a threshold of >5 puncta or 1 aggregate of chromogen in >25% of cells, was observed in 69 of 685 mimics (10.1%), spanning an array of mesenchymal tumors. Taken together, these findings suggest that, with careful interpretation and the use of appropriate thresholds, CHRNA6 RNA chromogenic in situ hybridization is a potentially useful ancillary histologic tool for the diagnosis of EMC.

Selected Case From the Arkadi M. Rywlin International Pathology Slide Seminar: Involvement of Skin and Soft Tissue by Erdheim-Chester Disease.

Erdheim-Chester disease is a rare form of non-Langerhans cell histiocytosis that preferentially involves long bones but can affect a variety of other organs. Initial presentation with extraskeletal involvement is not unusual and is most commonly observed in the central nervous system, heart, retroperitoneum, lungs, and skin. Initial presentation of the disease as a subcutaneous soft tissue mass is exceedingly rare and may pose difficulties for diagnosis. We describe a case of Erdheim-Chester disease that initially presented as a cutaneous and subcutaneous soft tissue mass in the right posterior shoulder of a 52-year-old man.

Sclerosing epithelioid fibrosarcoma of bone with hybrid features: clinicopathologic, radiologic, and molecular analysis of three cases.

Sclerosing epithelioid fibrosarcoma (SEF) occurring as a primary bone tumor is exceptionally uncommon. Even more rare are cases of SEF that show morphologic overlap with low-grade fibromyxoid sarcoma (LGFMS). Such hybrid lesions arising within the bone have only rarely been reported in the literature. Due to their variegated histomorphology and non-specific radiologic features, these tumors may pose diagnostic difficulties. Herein we describe three molecularly confirmed primary bone cases of sclerosing epithelioid fibrosarcoma that demonstrated prominent areas showing the features of LGFMS and with areas resembling so-called hyalinizing spindle cell tumor with giant rosettes (HSCTGR). Two patients were female and one was male aged 26, 47, and 16, respectively. The tumors occurred in the femoral head, clavicle, and temporal bone. Imaging studies demonstrated relatively well-circumscribed radiolucent bone lesions with enhancement on MRI. Cortical breakthrough and soft tissue extension were present in one case. Histologically the tumors all demonstrated hyalinized areas with SEF-like morphology as well as spindled and myxoid areas with LGFMS-like morphology. Two cases demonstrated focal areas with rosette-like architecture as seen in HSCTGR. The tumors were all positive for MUC4 by immunohistochemistry and cytogenetics, fluorescence in-situ hybridization, and next-generation sequencing studies identified EWSR1 gene rearrangements confirming the diagnosis in all three cases.Hybrid SEF is exceedingly rare as a primary bone tumor and can be difficult to distinguish from other low-grade spindled and epithelioid lesions of bone. MUC4 positivity and identification of underlying EWSR1 gene rearrangements help support this diagnosis and exclude other tumor types.

Thymic Parenchymal Hyperplasia.

Thymic hyperplasia is a rare condition generally caused by lymphoid follicular hyperplasia associated with autoimmune disorders. True thymic parenchymal hyperplasia unassociated with lymphoid follicular hyperplasia is extremely rare and may give rise to difficulties in diagnosis. We have studied 44 patients with true thymic hyperplasia (38 females and 6 males) aged 7 months to 64 years (mean, 36 years). Eighteen patients presented with symptoms of chest discomfort or shortness of breath; in 20 patients, the lesions were discovered incidentally. Imaging studies demonstrated enlargement of the mediastinum by a mass lesion suspicious for malignancy. All patients were treated with complete surgical excision. The tumors measured from 3.5 to 24 cm (median, 10 cm; mean, 10.46 cm). Histologic examination showed lobules of thymic tissue displaying well-developed corticomedullary architecture, with scattered Hassall corpuscles separated by mature adipose tissue and bounded by a thin fibrous capsule. No cases showed evidence of lymphoid follicular hyperplasia, cytologic atypia, or confluence of the lobules. Immunohistochemical studies showed a normal pattern of distribution for keratin-positive thymic epithelial cells against a background rich in CD3/TdT/CD1a+ lymphocytes. Twenty-nine cases had an initial clinical or pathological diagnosis of thymoma or thymoma vs thymic hyperplasia. Clinical follow-up in 26 cases showed that all patients were alive and well between 5 and 15 years after diagnosis (mean, 9 years). Thymic parenchymal hyperplasia causing significant enlargement of the normal thymus that is sufficient to cause symptoms or worrisome imaging findings should be considered in the differential diagnosis of anterior mediastinal masses. The criteria for distinguishing such lesions from lymphocyte-rich thymoma are presented.

Psammomatous calcifications in thyroid oncocytic (Hürthle cell) follicular tumors.

Concentric calcifications, also known as psammoma bodies, are a relatively frequent finding in certain types of tumors, particularly papillary thyroid carcinoma (PTC). In the thyroid, they have been assigned a significant role in the diagnosis of PTC and in distinguishing between these tumors and other types of thyroid neoplasms. Concentric calcifications have also less commonly been noted in other processes in the thyroid, such as in tumors characterized by cells containing abundant oxyphilic cytoplasm (i.e., Hürthle cells). We have studied 12 patients with oncocytic thyroid follicular tumors that contained scattered psammomatous calcifications that led to difficulties in diagnosis. The patients were 9 women and 3 men, aged 34 to 63 years. 10 cases corresponded to benign, non-invasive oncocytic tumors and 2 cases were minimally invasive follicular carcinomas of oncocytic (so called Hürthle cell) type. The psammomatous calcifications were randomly scattered throughout the lesions and were present as a focal, incidental finding in 8 cases and were diffuse in 4 cases. They were composed of concentrically laminated deposits of dense basophilic material closely resembling psammoma bodies, often associated with more homogeneous deposits of lightly eosinophilic material without concentric lamination that were interpreted as precipitated thyroglobulin. Seven patients with clinical follow-up, including one with minimally invasive carcinoma, were alive and well between 5 and 12 years after diagnosis. Concentric laminated calcifications may be encountered in oncocytic (Hürthle cell) follicular tumors and should not be interpreted as indicative of PTC in the context of oncocytic neoplasms of the thyroid.

Pulmonary nodular elastosis: The intraparenchymal counterpart of pulmonary apical caps?

We have studied six cases in which focal consolidative pulmonary opacities observed on imaging studies led to surgical resection due to the suspicion of malignancy and showed on histopathologic examination a benign process characterized by an expansile tumor-like nodular accumulation of elastotic material. The patients were five women and one man aged 46 to 67 years (mean: 61 years). All lesions were found incidentally on imaging studies done for a variety of reasons, including surveillance for metastatic carcinoma in four patients. The lesions presented as solid nodules within lung parenchyma with irregular borders and spiculated margins and measured between 0.6 and 4.6 cm in diameter. Histological examination showed dense deposits of elastic tissue without evidence of malignancy, similar to those seen in pulmonary apical caps. Clinical follow-up between 5 and 16 years (mean: 10 years) showed that all patients were alive and well without evidence of disease. Pulmonary nodular elastosis is a localized intraparenchymatous process that may be confused clinically and radiographically for a malignant neoplasm and needs to be distinguished from other nodular lesions of the lung. To the best of our knowledge, tumor-forming lesions within lung parenchyma that are predominantly or almost exclusively composed of accumulation of elastic fibers have not been previously described.

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.

Meningothelial Hamartoma of the Scalp: Clinicopathologic Review of an Unusual Tumor Mimicking a Vascular Neoplasm With Review of Literature.

ABSTRACT: An unusual benign skin lesion is reported in a 19-year-old man with no significant medical history. The lesion had been present since he was an infant and had been slowly enlarging over the past 15 years. The lesion caused pain and discomfort, and the patient underwent an excisional biopsy. Histologic examination showed a subcutaneous lesion with ill-defined borders and peripheral areas of infiltration between adnexal structures. The lesion was composed of small round to ovoid cells embedded in a collagenous stroma with prominent cystic pseudovascular appearing channels causing a pseudopapillary or lymphangitic appearance that mimicked a vascular neoplasm. Immunohistochemistry performed showed positive staining for EMA, progesterone receptor, D2-40, and vimentin within the lesional cells. The tumor cells were negative for cytokeratin AE1/AE3, CD34, CD31, HHV-8, STAT6, SMA, Desmin, S-100, Melan A, and HMB45. A next-generation sequencing study using a hybrid capture-based panel examining 50 commonly mutated genes in human neoplasia was performed and showed no molecular alterations suggesting a nonneoplastic nature. Based on the clinical presentation, histologic features, and results of ancillary studies, the case was diagnosed as a hamartoma of the scalp with meningothelial-like elements. Reported cases of this lesion have behaved in a benign manner; however, as the histologic differential includes low-grade malignant vascular neoplasms such as angiosarcoma, it is important to recognize the salient features of this lesion.

Immature Chondroid Choristoma: Clinicopathologic, Immunohistochemical, and Molecular Study of an Unusual Benign Skin Tumor.

ABSTRACT: An unusual benign skin tumor is reported occurring in a 68-year-old woman with no significant medical history. The lesion presented as a small skin nodule in the neck. Histologic examination showed a well-circumscribed superficial dermal nodule composed of a solid proliferation of large, round cells with abundant eosinophilic cytoplasm and small centrally placed nuclei displaying a vaguely chondroid appearance. Immunohistochemical studies showed strong positivity of the tumor cells for S100 protein and vimentin and negative staining for SOX10, melanoma cocktail, HMB45, Melan-A, cytokeratin AE1/AE3, inhibin, desmin, smooth muscle actin, CD68, CD164, and neuron specific enolase. Next-generation sequencing using a panel of 50 actionable genes commonly encountered in human neoplasia did not reveal the presence of any mutations. Owing to the remarkable similarity of the lesion to immature cartilage, we consider this to be a benign tumor, most likely resulting from an embryologic defect. We propose the term immature chondroid choristoma to designate this lesion.

Spindle cell tumors of the mediastinum.

Spindle cell tumors originating in the mediastinum are extremely rare. Due to the profusion of structures and organs located in the mediastinum, a wide variety of spindle cell neoplastic processes can develop in this location. These include various different tumor types including epithelial, vascular, lipomatous, fibroblastic and neural tumors among others. Many of these different tumor types are associated with specific immunohistochemical and molecular genetic profiles that help differentiate them from each other. Although spindle cell morphology has traditionally been associated with mesenchymal neoplasms, in the mediastinum the most common spindle cell tumor is spindle cell thymoma, an epithelial rather than mesenchymal neoplasm. Except for neurogenic tumors originating in the posterior mediastinum, mesenchymal neoplasms are quite rare in mediastinal locations and require clinical correlation to rule out the possibility of a metastasis from an extra-mediastinal soft tissue or somatic sarcoma. Herein we will review the most common types of spindle cell neoplasms that occur in the mediastinum, with particular emphasis in their differential diagnosis and the role of ancillary techniques for diagnosis.

The differential immune response in mild versus fatal SARS-CoV2 infection.

This study compared the immune response in mild versus fatal SARS-CoV2 infection. Forty nasopharyngeal swabs with either productive mild infection (n = 20) or negative for SARS-CoV2 (n = 20) were tested along with ten lung sections from people who died of COVID-19 which contained abundant SARS-CoV2 and ten controls. There was a 25-fold increase in the CD3+T cell numbers in the viral positive nasopharyngeal swabs compared to the controls (p < 0.001) and no change in the CD3+T cell count in the fatal COVID-19 lungs versus the controls. CD11b + and CD206+ macrophage counts were significantly higher in the mild versus fatal disease (p = 0.002). In situ analysis for SARS-CoV2 RNA found ten COVID-19 lung sections that had no/rare detectable virus and also lacked the microangiopathy typical of the viral positive sections. These viral negative lung tissues when compared to the viral positive lung samples showed a highly significant increase in CD3+ and CD8 T cells (p < 0.001), equivalent numbers of CD163+ cells, and significantly less PDL1, CD11b and CD206+ cells (p = 0.002). It is concluded that mild SARS-CoV2 infection is marked by a much stronger CD3/CD8 T cell, CD11b, and CD206 macrophage response than the fatal lung disease where viral RNA is abundant.

Oncocytic nodular hyperplasia of the thyroid.

Nodular hyperplasia of the thyroid is a process whereby the gland experiences growth by nodular expansion of thyroid parenchyma. We have encountered 45 patients in whom the process was caused by the growth of well-defined and sharply circumscribed but unencapsulated nodules composed of oncocytic thyroid follicular cells. The lesions arose in 39 women and 6 men, aged 25-69 years (mean = 50.3 years). The surrounding thyroid parenchyma showed features of chronic lymphocytic thyroiditis. The nodules varied from microscopic to 5 cm and appeared to compress the surrounding thyroid parenchyma. Most of the lesions lacked a well-defined capsule. In 26 tumors, the nodules displayed a predominantly follicular pattern of growth; in 8 cases there were admixtures of follicular and trabecular patterns with focal solid areas devoid of follicles. Clinical follow-up in 39 patients ranging from 7 to 22 years (median = 16 years) showed no evidence of recurrence, metastasis, or malignant transformation. One patient died of unknown causes 15 years after the diagnosis, and another patient died 4 years after diagnosis from metastatic colonic adenocarcinoma. Oncocytic nodular hyperplasia is a benign process associated with chronic lymphocytic thyroiditis that should be distinguished from benign and malignant oncocytic (Hurthle cell) tumors of the thyroid.

The histologic and molecular correlates of liver disease in fatal COVID-19 including with alcohol use disorder.

Hepatic disease is common in severe COVID-19. This study compared the histologic/molecular findings in the liver in fatal COVID-19 (n = 9) and age-matched normal controls (n = 9); three of the fatal COVID-19 livers had pre-existing alcohol use disorder (AUD). Controls showed a high resident population of sinusoidal macrophages that had variable ACE2 expression. Histologic findings in the cases included periportal/lobular inflammation. SARS-CoV2 RNA and nucleocapsid protein were detected in situ in 2/9 COVID-19 livers in low amounts. In 9/9 cases, there was ample in situ SARS-CoV-2 spike protein that co-localized with viral matrix and envelope proteins. The number of cells positive for spike/100× field was significantly greater in the AUD/COVID-19 cases (mean 5.9) versus the non-AUD/COVID-19 cases (mean 0.4, p < 0.001) which was corroborated by Western blots. ACE2+ cells were 10× greater in AUD/COVID-19 livers versus the other COVID-19/control liver samples (p < 0.001). Co-expression experiments showed that the spike protein localized to the ACE2 positive macrophages and, in the AUD cases, hepatic stellate cells that were activated as evidenced by IL6 and TNFα expression. Injection of the S1, but not S2, subunit of spike in mice induced hepatic lobular inflammation in activated macrophages. It is concluded that endocytosed viral spike protein can induce hepatitis in fatal COVID-19. This spike induced hepatitis is more robust in the livers with pre-existing AUD which may relate to why patients with alcohol abuse are at higher risk of severe liver disease with SARS-CoV2 infection.

Histologic, viral, and molecular correlates of heart disease in fatal COVID-19.

Cardiac manifestations are common in severe COVID-19. This study compared the histologic, viral, and molecular findings in cardiac tissue in fatal COVID-19 (n = 11) and controls (n = 11). In situ hybridization (SARS-CoV2 RNA) and immunohistochemistry for viral proteins and the host response were quantified for the samples and compared with qRTPCR and Western blot data. Control hearts showed a high resident population of macrophages that had variable ACE2 expression. Cardiac ACE2 expression was 10× greater in the heart tissues of cases and controls with obesity or type II diabetes. Multifocal endothelial cell swelling and degeneration, perivascular edema plus microvascular thrombi were unique to the cases. SARS-CoV2 RNA and nucleocapsid protein were rarely detected in situ in any COVID-19 heart. However, in each case abundant SARS-CoV-2 spike protein was evident. Co-expression experiments showed that the spike protein localized mostly to the ACE2+ interstitial macrophages/pericytes that were activated as evidenced by increased IL6 and TNFα expression. Western blots confirmed the presence of the viral spike protein, but not the nucleocapsid protein, in the cardiac homogenates. The intercalated disc proteins connexin 43, the primary cardiac gap junction protein, and NaV1.5, the predominant cardiac sodium channel, each showed marked lateral migration in the myocytes in the cases, which would increase the risk of reentrant arrhythmias. It is concluded that the viral spike protein, endocytosed by macrophages/pericytes, can induce a myocarditis with the possibility of conduction dysfunction due to abnormal localization of key intercalated disc proteins.

The amplification of CNS damage in Alzheimer's disease due to SARS-CoV2 infection.

Pre-existing Alzheimer's disease is a risk factor for severe/fatal COVID-19 and infection by SARS-CoV2 virus has been associated with an increased incidence of un-masked Alzheimer's disease. The molecular basis whereby SARS-CoV2 may amplify Alzheimer's disease is not well understood. This study analyzed the molecular changes in autopsy brain tissues from people with pre-existing dementia who died of COVID-19 (n = 5) which was compared to equivalent tissues of people who died of COVID-19 with no history of dementia (n = 8), Alzheimer's disease pre-COVID-19 (n = 10) and aged matched controls (n = 10) in a blinded fashion. Immunohistochemistry analyses for hyperphosphorylated tau protein, α-synuclein, and ß-amyloid-42 confirmed the diagnoses of Alzheimer's disease (n = 4), and Lewy body dementia (n = 1) in the COVID-19 group. The brain tissues from patients who died of COVID-19 with no history of dementia showed a diffuse microangiopathy marked by endocytosis of spike subunit S1 and S2 in primarily CD31+ endothelia with strong co-localization with ACE2, Caspase-3, IL6, TNFα, and Complement component 6 that was not associated with SARS-CoV2 RNA. Microglial activation marked by increased TMEM119 and MCP1 protein expression closely paralleled the endocytosed spike protein. The COVID-19 tissues from people with no pre-existing dementia showed, compared to controls, 5-10× fold increases in expression of neuronal NOS and NMDAR2 as well as a marked decrease in the expression of proteins whose loss is associated with worsening Alzheimer's disease: MFSD2a, SHIP1, BCL6, BCL10, and BACH1. In COVID-19 tissues from people with dementia the widespread spike-induced microencephalitis with the concomitant microglial activation co-existed in the same areas where neurons had hyperphosphorylated tau protein suggesting that the already dysfunctional neurons were additionally stressed by the SARS-CoV2 induced microangiopathy. ACE2+ human brain endothelial cells treated with high dose (but not vaccine equivalent low dose) spike S1 protein demonstrated each of the molecular changes noted in the in vivo COVID-19 and COVID-19/Alzheimer's disease brain tissues. It is concluded that fatal COVID-19 induces a diffuse microencephalitis and microglial activation in the brain due to endocytosis of circulating viral spike protein that amplifies pre-existing dementia in at least two ways: 1) modulates the expression of proteins that may worsen Alzheimer's disease and 2) stresses the already dysfunctional neurons by causing an acute proinflammatory/hypercoagulable/hypoxic microenvironment in areas with abundant hyperphosphorylated tau protein and/or ßA-42.

Expression patterns for Bcl-2, EMA, ß-catenin, E-cadherin, PAX8, and MIB1 in thymomas.

The expression of immunohistochemical markers has been extensively investigated in thymomas to assist in the differential diagnosis. We have studied six select markers to determine their utility in the evaluation of these tumors. A series of 126 thymomas including 33 type A, 27 type AB, 20 type B1, 22 type B2, and 24 type B3, were examined utilizing a tissue microarray (TMA) technique with antibodies to e-cadherin, ß-catenin, PAX8, bcl-2, EMA, and MIB-1. Keratin AE1/AE3 and p63 were used for quality control. A significant finding was strong and consistent positivity for bcl-2 in type A (90%) and type AB (88.8%) thymoma, while 100% of B1, B2, and B3 were negative. The distribution of e-cadherin and ß-catenin was not useful for differential diagnosis. E-cadherin and ß-catenin were expressed in a high proportion of all the tumors (92-100%), except for B2 thymoma which showed only 45% expression. A significant increase in the expression of the MIB-1 proliferation marker (mean: 12.8% nuclear positivity) was also observed in B3 thymoma compared with the other histologic types. Statistical significance was confirmed using Kruskal's non-parameterized test for distribution. EMA was generally negative except for spindle cells in the fibrous septa in types A and AB thymoma. PAX8 showed less consistent nuclear staining than p63 and was only widely expressed in 55.7% of cases. Bcl-2 may serve as a useful marker to separate spindle cell thymomas (Type A and AB) from the other types, and the MIB1 proliferation index may be of use to differentiate type B2 from type B3 thymoma.

Histologic Patterns of Cutaneous Metastases of Breast Carcinoma: A Clinicopathologic Study of 232 Cases.

ABSTRACT: Cutaneous metastasis may be the initial sign of internal malignancy but more often represents a late manifestation of widely disseminated disease. Breast carcinoma is the most common malignancy to metastasize to the skin. Although several studies have detailed the histopathologic patterns of cutaneous metastasis from internal malignancies, very little has been published regarding metastases of breast carcinoma to the skin. Furthermore, the histopathologic and clinical features observed in the cases of breast carcinoma with local skin involvement as opposed to cases exhibiting distant cutaneous metastases have not been adequately investigated. We have reviewed 232 cases of breast carcinoma with cutaneous metastases from 2 large institutions. All cases of carcinoma of the breast with involvement of the skin of the anterior chest wall were compared with those with distant cutaneous metastases. Two hundred thirty-two cases in 199 patients were included, of which 126 had skin involvement exclusively involving the ipsilateral anterior chest, and 106 had biopsy-proven distant cutaneous metastases. Twelve patients had both local and distal spread. Distant cutaneous metastases showed a predilection for the contralateral anterior chest wall area, followed by the head and neck, back, and abdomen. Histologically, most of the tumors presented in this series showed features of infiltrating ductal carcinoma. In both ipsilateral and distant metastases, the tumors demonstrated little change in histologic features from the primary lesion; however, the distant metastases showed a tendency to display more poorly differentiated features. The mean patient survival when cutaneous involvement was localized to the skin of the anterior chest wall was 23 months as compared with 20.6 months when distant sites were affected. A comparison of the clinicopathologic features of the patients presented in this series suggests that alternate biological mechanisms may apply for local and distant skin metastases from breast carcinoma.

Endothelial cell damage is the central part of COVID-19 and a mouse model induced by injection of the S1 subunit of the spike protein.

Neurologic complications of symptomatic COVID-19 are common. Brain tissues from 13 autopsies of people who died of COVID-19 were examined. Cultured endothelial and neuronal cells were incubated with and wild type mice were injected IV with different spike subunits. In situ analyses were used to detect SARS-CoV-2 proteins and the host response. In 13/13 brains from fatal COVID-19, pseudovirions (spike, envelope, and membrane proteins without viral RNA) were present in the endothelia of microvessels ranging from 0 to 14 positive cells/200× field (mean 4.3). The pseudovirions strongly co-localized with caspase-3, ACE2, IL6, TNFα, and C5b-9. The surrounding neurons demonstrated increased NMDAR2 and neuronal NOS plus decreased MFSD2a and SHIP1 proteins. Tail vein injection of the full length S1 spike subunit in mice led to neurologic signs (increased thirst, stressed behavior) not evident in those injected with the S2 subunit. The S1 subunit localized to the endothelia of microvessels in the mice brain and showed co-localization with caspase-3, ACE2, IL6, TNFα, and C5b-9. The surrounding neurons showed increased neuronal NOS and decreased MFSD2a. It is concluded that ACE2+ endothelial damage is a central part of SARS-CoV2 pathology and may be induced by the spike protein alone. Thus, the diagnostic pathologist can use either hematoxylin and eosin stain or immunohistochemistry for caspase 3 and ACE2 to document the endothelial cell damage of COVID-19.

Severe COVID-19: A multifaceted viral vasculopathy syndrome.

The objective of this study was to elucidate the pathophysiology that underlies severe COVID-19 by assessing the histopathology and the in situ detection of infectious SARS-CoV-2 and viral capsid proteins along with the cellular target(s) and host response from twelve autopsies. There were three key findings: 1) high copy infectious virus was limited mostly to the alveolar macrophages and endothelial cells of the septal capillaries; 2) viral spike protein without viral RNA localized to ACE2+ endothelial cells in microvessels that were most abundant in the subcutaneous fat and brain; 3) although both infectious virus and docked viral spike protein was associated with complement activation, only the endocytosed pseudovirions induced a marked up-regulation of the key COVID-19 associated proteins IL6, TNF alpha, IL1 beta, p38, IL8, and caspase 3. Importantly, this microvasculitis was associated with characteristic findings on hematoxylin and eosin examination that included endothelial degeneration and resultant basement membrane zone disruption and reduplication. It is concluded that serious COVID-19 infection has two distinct mechanisms: 1) a microangiopathy of pulmonary capillaries associated with a high infectious viral load where endothelial cell death releases pseudovirions into the circulation, and 2) the pseudovirions dock on ACE2+ endothelial cells most prevalent in the skin/subcutaneous fat and brain that activates the complement pathway/coagulation cascade resulting in a systemic procoagulant state as well as the expression of cytokines that produce the cytokine storm. The data predicts a favorable response to therapies based on either removal of circulating viral proteins and/or blunting of the endothelial-induced response.