WHO grading system for invasive pulmonary lung adenocarcinoma reveals distinct molecular signature: An analysis from the cancer genome atlas database.

Lung adenocarcinoma grading has gained interest in the past years. Recently a three-tier tumor grading was proposed showing that it is related to patients' prognosis. Nevertheless, the underlying molecular basis of this morphological grading remains partly unknown. The aim of our work is to take advantage of The Cancer Genome Atlas lung adenocarcinoma (TCGA_LUAD) cohort to describe the molecular data associated to tumor grading. We performed a study on publicly available data of the TCGA database first by assessing a tumor grade on downloadable tumor slides. Secondly we analyzed the molecular features of each tumor grade group. Our work was performed on a study group of 449 patients. We show that aneuploidy score was significantly different between grade 2 and grade 3 groups with different chromosomal imbalance (p < 0.001). SCGB1A1 mRNA expression was higher in grade 2 (p = 0.0179) whereas NUP155, CHFR, POLQ and CDC7 have a higher expression in grade 3 (p = 0.0189, 0.0427, 0.0427 and 0.427 respectively). GZMB and KRT80 have a higher methylation of DNA in grade 2 (p = 0.0201 and 0.0359 respectively). MT1G, CLEC12B and NDUFA7 have a higher methylation of DNA in grade 3 (p < 0.001, 0.0246 and 0.0359 respectively). We showed that the number of activated pathways is different between grade 2 and grade 3 patients (p = 0.004). We showed that differentially expressed genes by mRNA analysis and DNA methylation analysis involve several genes implied in chemoresistance. This could suggest that grade 3 lung adenocarcinoma might be more resistant to chemotherapy.

Histopathological and molecular profiling of lung adenocarcinoma skin metastases reveals specific features.

AIMS: Little is known regarding the histopathological and molecular features of lung adenocarcinoma skin metastases. Our study is the largest, to our knowledge, to comprehensively explore these to date. METHODS AND RESULTS: We performed a retrospective cohort study analysing 42 lung adenocarcinoma skin metastasis samples obtained from a database of 2659 lung adenocarcinomas collected between 2010 and 2020. EGFR exon 19 deletion was detected in one patient and KRAS mutations were detected in 12 (33.3%) patients. The programmed cell death ligand 1 (PD-L1) tumour proportion score was <1% in 27 patients, ≥1% and <50% in eight patients, ≥50% in six patients and not assessable in one patient. We showed that the predominant histopathological subtype is different from that at other metastatic sites (P = 0.024). Thyroid transcription factor I (TTF-1) was more often negative in skin metastases compared to other sites (P < 0.001). The EGFR mutation rate tended to be lower for skin metastases compared to other sites (P = 0.079). Skin metastases were associated with a high rate of PD-L1-negative cases (P = 0.022). CONCLUSION: Our work shows that the skin metastases of lung adenocarcinoma have a specific histopathological profile.

Glioma Associated Microglia/Macrophages Distribution is Conserved in Glioblastoma Regrowth: A Morphometric Study.

We compared the morphological aspect of glioblastoma-associated microglia/macrophages cells in 15 paired recurrent glioblastomas to check the ability of glioblastoma to recreate its microenvironment. The absolute number of GAMs is lower in normal tissue (21/mm2) than in the isolated tumor cells area (100-112/mm2) than in the solid tumor area (212-220/mm2) (p < 0.01). The morphology of GAMs remained the same in each tumor area with a reduced covered area by cell processes (196 to 216/mm2) than in normal tissue (708/mm2) (p < 0.01). In paired tumors, GAMs morphology remained the same in successive resections and was not modified by the treatments.

FOXA1 in HPV associated carcinomas: Its expression in carcinomas of the head and neck and of the uterine cervix.

BACKGROUND: FOXA1 is a major transcription factor involved in the action of human papilloma virus (HPV). However, it has been never studied in HPV-associated tumors. AIM OF THE STUDY: To investigate its expression in cervical and head and neck tumors. MATERIAL AND METHODS: 63 cervical carcinomas/dysplasias and 152 head and neck squamous cell carcinomas (HNSCC) were immunohistochemically studied for the expression of FOXA1. RESULTS: 63.1% of cervical SCC and 40.7% of endocervical adenocarcinomas strongly expressed FOXA1. Most (90%) pre-invasive lesions (CIN3 and in situ adenocarcinomas) strongly expressed FOXA1 and this difference from invasive lesions was statistically significant (p=0.005). No association with clinicopathological factors was found. 51.3% of HNSCC expressed FOXA1. In these tumors, FOXA1 expression was associated with the non-keratinizing morphology but not with the HPV/p16 status neither other clinicopathological features. Of normal structures, salivary glands, endocervical glands and basal/parabasal cell layer of squamous epithelium of both uterine cervix and head and neck mucosa, all strongly expressed FOXA1. CONCLUSION: FOXA1 is expressed by basal cells of squamous epithelium, pre-invasion lesions of the uterine cervix and the head/neck and almost half invasive cervical and head/neck carcinomas, supporting its possible implication in HPV pathogenesis.

EGFR, KRAS, BRAF and HER2 testing in metastatic lung adenocarcinoma: Value of testing on samples with poor specimen adequacy and analysis of discrepancies.

Molecular testing on metastatic lung adenocarcinoma or on non-small cell non-squamous lung carcinoma often relies on small specimen. In this group of patient with poor specimen adequacy, we analyzed the rate of EGFR, KRAS, BRAF and HER2 mutations compared to their rate in optimal specimen. We analyzed discrepancies in molecular testing results in patients with iterative analysis on several samples. We performed a retrospective study of 1538 samples consecutively analyzed. 263/665 (39,5%) biopsies and 37/708 (5,2%) surgical specimens were considered as samples with poor specimen adequacy (p<0,0001). A lower tumor cell content was associated with a lower rate of KRAS mutation: 15,8% in samples with <10% of tumor cells or <100 tumor cells versus 29,8% in samples with >10% tumor cell and >100 tumor cells (p=0,001). KRAS mutational rate was at 11,1% in cytology specimens, significantly lower than in biopsy or surgical specimens respectively at 28,2% and 28,5% (p=0,0002). Tumor cell content was not associated with mutational rate for EGFR, BRAF and HER2 mutations. DNA quantity was not associated with mutational rate for EGFR, KRAS, BRAF and HER2. A discrepancy in molecular testing was found in 16 patients. For 5 patients there was also a discrepancy for TTF-1 expression. On the 11 without TTF-1 discrepancy, specimen adequacy was not fulfilled in 10 cases at least for tumor content. Discrepancies were found in the case of low cellularity, poor cell content or testing on cytological specimens. Tumor cell content is a crucial parameter for molecular analysis rather than the type of specimen or the DNA quantity. Discrepancies in molecular testing results are rare but might suggest the presence of another tumor type, the emergence of another clone or a molecular testing in a sample with low cell content.

Eosinophilic Cells, Autoimplants, Degree of Cellular Proliferation, and Adenofibroma Pattern are Important Histologic Findings in Ovarian Borderline Tumors.

Ovarian borderline tumors can show histologic features, such as different degrees of cellular proliferation, eosinophilic cells, autoimplants, and adenofibromatous architecture, the importance of which is not known. The aim of the study was to describe these features and correlate them with clinical characteristics. Eighty-three ovarian borderline tumors were studied for the aforementioned features. These were correlated with clinicopathologic features. Epithelial proliferation was associated with the T stage in serous tumors (P=0.0009), but not in mucinous tumors (P=0.97). It was positively associated with bilateral tumors (P=0.01) and the presence of autoimplants (P<0.0001). It was associated with the presence of eosinophilic cells, as tumors with extensive eosinophilic cells had a mean proliferation of 80.7%, for those with no such cells it was 23.8% (P<0.0001), and for those with a limited presence of eosinophilic cells it was 48.7% (P=0.03). Cellular proliferation was not associated with the size of the tumor. An adenofibromatous architecture was associated with unilateral tumors (P=0.02) and showed a trend (P=0.08) with regard to T stage in serous tumors. It was not associated with the size of the tumor. The presence of autoimplants was marginally associated (P=0.07) with bilateral tumors and it was not associated with the size of the tumor or the T stage. The presence of eosinophilic cells was not associated with the T stage, the size of the tumor, or bilateral tumors. The degree of epithelial proliferation, autoimplants, adenofibromatous architecture, and the presence of eosinophilic cells are important features in ovarian borderline tumors.

Anti-CK7/CK20 Immunohistochemistry Did Not Associate with the Metastatic Site in TTF-1-Negative Lung Cancer.

Anti-CK7 and anti-CK20 immunohistochemistry is sometimes used to establish a diagnosis of primary lung cancer. We performed a retrospective study on the value of anti-CK7 and anti-CK20 immunohistochemistry in 359 biopsies of patients with suspected lung carcinoma in order to assess the usefulness of these antibodies in the evaluation of lung tumors in biopsies. Our results showed TTF-1 positivity in 73.3% of patients. EGFR mutations and ALK rearrangements were significantly different between TTF-1 positive and TTF-1 negative tumors (p < 0.001 and p = 0.023, respectively). Our results show a significant difference (p < 0.001) between TTF-1 positive and TTF-1 negative carcinomas with a median survival of 21.97 months (CI95% = 17.48−30.9 months) and 6.52 months (CI95% = 3.34−10.3 months), respectively. In the group of TTF-1 negative patients, anti-CK7 and CK20 immunohistochemistry was performed in 70 patients and showed CK7+/CK20- staining in 61 patients (87.1%), CK7-/CK20- in 4 patients (5.7%), CK7+/CK20+ in 3 patients (4.3%), and CK7-/CK20- in 2 patients (2.8%). No specific or molecular pattern was found in these groups of CK7/CK20 combinations. In total, this work brings arguments concerning the uselessness of anti-CK7/CK20 immunohistochemistry in the case of suspicion of primary lung cancer in biopsies.

Incidental Detection of a Small Cell Lung Cancer by 18F-Choline PET/CT Performed for Recurrent Hyperparathyroidism After Parathyroidectomy.

ABSTRACT: We report the case of a 64-year-old woman with musculoskeletal pain and elevated serum parathyroid hormone who had undergone parathyroidectomy for primary hyperparathyroidism 4 years earlier. An 18F-choline PET/CT scan was performed and incidentally showed an intense uptake in a right upper lobe pulmonary nodule and in the right hilar, mediastinal, and cervical lymph nodes. Histopathological analysis confirmed the diagnosis of a small cell lung cancer. Clinical symptoms and recurrent hyperparathyroidism were therefore consistent with a paraneoplastic syndrome. A complete metabolic response was achieved on 18F-FDG PET/CT scan after chemotherapy.

Mesothelial Cysts.

OBJECTIVES: Peritoneal mesothelial cysts have been reported under various terms, including benign cystic mesothelioma, usually in the form of case reports/series, whereas extraperitoneal cases are rarely reported. Our objective was to report the detailed characteristics of cystic lesions of the serosal cavities. METHODS: We retrospectively examined the clinicopathologic findings of a series of mesothelial cystic lesions (n = 79). RESULTS: Most cases (n = 68, 86%) concerned the peritoneum, whereas 11 (14%) concerned the pericardium. No pleural cases were found. A total of 51 (64.5%) lesions were solitary, whereas 28 (35.5%) were multiple. Peritoneal lesions harbored a plump eosinophilic mesothelium and a loose connective stroma, whereas pericardial lesions showed a cuboidal/flattened mesothelium, collagenous stroma, intense inflammation, and other tissue types, like adipose and muscle tissue. Solitary peritoneal lesions are usually extrapelvic and found in older patients incidentally during other surgeries, whereas multiple lesions are found in younger patients and usually in the pelvis. The lesions show a benign clinical course with rare recurrences but no malignant transformation. CONCLUSIONS: Most mesothelial cysts are peritoneal and rarely pericardial. Peritoneal cysts differ from pericardial cysts. Peritoneal solitary lesions differ from multiple lesions, also suggesting their pathogenetic differences.

Heterogeneity of PD-L1 expression in lung adenocarcinoma metastasis is related to histopathological subtypes.

OBJECTIVES: The heterogeneity of PD-L1 expression and its relationship with histopathological subtype has recently been shown on primary tumor but has not been evaluated on metastases. The aim of our work is to analyze PD-L1 expression within each histopathological pattern on resected metastases. MATERIAL AND METHODS: 136 patients were included in this retrospective study. Immunohistochemistry was performed with 22C3 laboratory-developed test. The Tumor Proportion Score was evaluated on each subtype. RESULTS: The most frequent major histopathological subtype was solid (n = 69, 50.7 %), followed by acinar (n = 37, 27.2 %), micropapillary (n = 14, 10.3 %) and papillary (n = 10, 7.3 %). Mean percentage of PD-L1 expression for each subtype was at 28+/-4.8 % for solid subtype, 5.3+/-1.9 % for acinar subtype, 5+/-1.9 % for papillary subtype and 23.6+/-4.1 % for micropapillary subtype. Mean percentage of PD-L1 expression was different between solid pattern and acinar pattern (p < 0.001), solid pattern and papillary pattern (p = 0.007), micropapillary pattern and acinar pattern (p < 0.001) and micropapillary pattern and papillary pattern (p = 0.015). CONCLUSION: To conclude, we have showed firstly that several patterns are present in metastases of lung adenocarcinoma, secondly that the evaluation of patterns and PD-L1 stain on different patterns is reproducible, thirdly that pattern heterogeneity is related to PD-L1 staining, fourthly that in metastatic lung adenocarcinoma with at least two patterns, solid and micropapillary subtypes have higher levels of PD-L staining, fifthly that PD-L1 heterogeneity between different patterns is not a rare event. These results might explain discrepancies of PD-L1 results between biopsies and surgical samples and the fact that some patients might respond to checkpoint inhibitors even though PD-L1 expression is low or absent.

High endothelial venules are present in pharyngeal and laryngeal carcinomas and they are associated with better prognosis.

BACKGROUND: Tumors lymphocytic infiltration has prognostic and predictive value. However, the mechanisms involved in lymphocyte recruitment remain poorly characterized. High endothelial venules (HEV) are blood vessels specialized in lymphocyte recruitment, recently showing prognostic significance in some types of cancer. Their implications in laryngeal or pharyngeal cancer is largely unknown. AIM OF THE STUDY: To investigate the possible presence of HEVs in head and neck cancer. MATERIAL AND METHODS: Oropharyngeal (n = 61), hypopharyngeal (n = 53) and laryngeal (n = 21) squamous cell carcinomas were immunohistochemically studied with the MECA-79 antibody, which specifically recognizes HEVs. Histological and clinical factors were correlated with HEVs' presence. RESULTS: HEVs were present in 34% of tumors, showing significant correlations with oropharyngeal localization, higher lymphocytic response, lower tumor budding, lower T status, absence of distant metastases and better overall and progression-free survival. CONCLUSION: HEVs represent an important prognostic factor in head and neck cancer.

Immune Escape Is an Early Event in Pre-Invasive Lesions of Lung Squamous Cell Carcinoma.

Bronchial dysplasia is the pre-neoplastic lesion recognized for invasive squamous cell carcinoma. The mechanisms leading to invasive squamous cell carcinoma for this lesion are not fully known. Programmed Death-Ligand 1 (PD-L1) expression by the bronchial dysplasia neoplastic epithelium might suggest a response to immunotherapy. The objective of this work is to further characterize PD-L1 and CD8 expression in bronchial dysplasia and bronchial metaplasia compared to normal bronchial epithelium. Immunohistochemical analysis of PD-L1 and CD8 staining were characterized in bronchial dysplasia of 24 patients and correlated with clinical data. We also compared PD-L1 expression in dysplasia samples to 30 normal epithelium and 20 samples with squamous bronchial metaplasia. PD-L1 was never expressed in normal epithelium and in metaplastic epithelium whereas 37.5% of patients with bronchial dysplasia were stained by PD-L1 (p < 0.001). PD-L1 expression was not related to the degree of dysplasia or a medical history of invasive squamous cell carcinoma, while CD8 expression and its localization were related to medical history of squamous cell carcinoma (p = 0.044). Our results show that PD-L1 is expressed in roughly one third of patients with bronchial dysplasia and is not expressed in normal and metaplastic epithelium. This suggests that PD-L1 is expressed in preneoplastic lesions of squamous cell carcinoma.

Histopathological and molecular study for synchronous lung adenocarcinoma staging.

The presence of multiple synchronous lung cancer with the same histopathological type for a patient is a common situation and an issue for staging. Pathological criteria exist to distinguish multiple primaries from intra-pulmonary metastases of the same tumor, but they lack standardization. We wondered how molecular analysis with a limited Next Generation Sequencing panel could bring further information for tumor staging in this setting. We analyzed 24 patients with a total of 50 tumor nodules (22 pairs, two triplets). We compared histopathological examination with molecular analysis. A total of 50 tumors were molecularly tested. Nucleoli size was associated with molecular analysis concordance (p = 0.047). The presence of lepidic component in any of the two larger tumors was associated with molecular analysis concordance (p = 0.012). For molecular analysis, the proportion of progression-free patients was at the limits of significance (p = 0.054) whereas the presence of lepidic component, architectural concordance, and the concordance of comprehensive histologic assessments was not related to progression-free survival. For two patients with a discordant TTF-1 immunohistochemistry, molecular analysis showed a different mutation. Our results show that a limited NGS panel brings supplementary data to classify synchronous lung adenocarcinoma in most patients. We show that molecular staging seems in accordance with progression-free survival. Histopathological examination alone might not be accurate enough to assess a correct staging for synchronous tumors. We also suggest that TTF-1 immunohistochemistry, for the rare discrepant cases, might be a surrogate to molecular analysis.

TTF-1-positive Metastatic Endometrioid Carcinoma: A Case Report and Review of Literature of a Potential Diagnostic Pitfall.

A 75-year-old female patient, nonsmoker was addressed to our institution for a fracture of C5 vertebra with spinal cord compression by a tumor mass invading surrounding soft tissue. She had a previous history of breast ductal carcinoma and endometrioid carcinoma. Biopsy of the tumor mass showed a TTF-1-positive carcinoma. Molecular study showed a E545K mutation of PIK3CA. Lung imaging showed multiple nodules evocative of metastasis rather than a primitive tumor. Reviewing of slides of endometrioid carcinoma showed areas positive for TTF1, and the same E545K mutation was found in endometrial tumor. The final diagnosis was endometrioid metastatic carcinoma with aberrant TTF-1 expression. A subset of endometrial neoplasm expresses TTF-1, this situation might be confusing especially in case of metastatic disease.

Brain metastasis PD-L1 and CD8 expression is dependent on primary tumor type and its PD-L1 and CD8 status.

BACKGROUND: Brain metastases (Bmets) are frequent; however, limited data exist on the efficacy of immunotherapy in these lesions. The aims of the study were to analyze the immunohistochemical expressions of programmed death ligand 1 (PD-L1) and CD8 in Bmets and to compare them with their expressions in paired primary tumors, as well as correlate the results with clinicopathological features. METHODS: This is a retrospective study of 233 patients with Bmets and 111 paired primaries. Clinical, histological, and molecular data were recorded and compared with the immunohistochemical results of PD-L1 and CD8 expressions. The statistical analysis included χ2 test, Cramer's V test, factorial analyses of variance, simple regression analysis, and Kaplan-Meier analysis with log-rank product limit estimation. RESULTS: PD-L1 expression was found in 23.6% of Bmets and in 29.0% of primary tumors with concordant expression between them in 75.5% of cases. Bmets PD-L1 expression was associated with primary tumor PD-L1 expression and the primary tumor type. Significant CD8 peritumoral expression was found in 68.6% of Bmets and in 87.7% of primary tumors. CD8 expression was concordant between primary and metastatic tumors in 73.3% of cases. Bmets CD8 expression was associated with primary tumor CD8 expression and primary tumor type. PD-L1 expression was associated with CD8 expression in both primary and metastatic tumors. The concordance between primary and metastatic tumor PD-L1 expression was independent of all factors studied. The concordance between primary and metastatic CD8 expressions was marginally associated to the time of Bmets development. No prognostic role for PD-L1 and CD8 expression in Bmets was found. CONCLUSION: PD-L1 and CD8 Bmets expressions are associated with the primary tumor type and its PD-L1 and CD8 expressions. No factor predicts the discordance for PD-L1 expression, while time to Bmets development is associated with CD8 expression discordance.

Histopathological subtyping is a prognostic factor in stage IV lung adenocarcinoma.

Lung adenocarcinoma is a heterogeneous tumor made of different architectural patterns. These tumors are classified into subtypes according to the predominant pattern in the primary tumor because the predominant pattern is related to overall survival. The prognostic role of these subtypes in stage IV disease is not well known, and most lung adenocarcinomas are diagnosed at the stage of metastatic disease. We aimed to evaluate the prognostic role of histopathological subtypes in lung adenocarcinoma metastases in a retrospective study of 253 patients with clinical, histopathological and molecular data. The presence of the solid subtype was related to overall survival (p = 0.045); the median overall survival was 6.8 months (95 % confidence interval (95 %CI) 4.4-9.1) when present and 11.1 months (95 %CI 8.6-21.3) when absent. Thyroid transcription factor 1 (TTF-1) immunohistochemistry was related to overall survival (p < 0.001); the median overall survival was 11.2 months (95 %CI 8.4-17.7) when positive and 4 months (95 %CI 2.3-5.7) when negative. On multivariate analysis, the presence of the solid subtype (p = 0.0036, hazard ratio (HR) 1.55, 95 %CI 1.03-2.34), TTF-1 positivity (p = 0.044, HR 0.64, 95 %CI 0.42-0.98), age <60 years at the time of resection (p = 0.017, HR 1.89; 95 %CI 1.12-3.21), performance status <2 (p = 0.017, HR 0.57; 95 %CI 0.36-0.91), treatment by chemotherapy (p = 0.033, HR 0.54, 95 %CI 0.31-0.95), and treatment by tyrosine kinase inhibitor or immunotherapy (p = 0.013, HR 0.36, 95 %CI 0.17-0.81) were related to overall survival. The evaluation of architectural pattern in metastases in stage IV patients provides further information for physicians about patient prognosis. This information might be included in clinical trials in patients with stage IV lung adenocarcinoma.

Clinical long-term outcome of non-specific pleuritis (NSP) after surgical or medical thoracoscopy.

BACKGROUND: Thoracoscopy, either "medical" or "surgical", is the gold standard to reveal the cause of pleural effusion by taking large biopsies. However, in some cases, the histology of pleural biopsies is inconclusive for a specific cause, describing a variable process of inflammation, encompassing for non-specific pleuritis (NSP). Questions are raised whether the surgical (or video-assisted thoracoscopic surgery, VATS) is doing better than the medical thoracoscopy (MT or pleuroscopy), but no direct comparison between the two techniques exist in the current bibliography. The aim of our retrospective study was to compare these two techniques to find whether there is any difference in the false negative cases of NSP. METHODS: We included in our study 295 patients with NSP, 179 patients who underwent VATS comparing to 116 patients who underwent MT for pleural effusion of initially undetermined cause, having a follow-up of at least one year. Analysis of patients' files, history, clinical examinations, further tests, and follow-up were recorded. RESULTS: The mean age of our patients was 58.5±19.1 and M/F gender was 216/79; no difference was observed between the two groups. The mean follow-up period was 47.3±20.7 months. After VATS, only one patient (0.55%) was finally diagnosed with pleural malignancy (false negative) while after MT 2 patients (1.7%). Negative predictive value for pleura-related malignancy for VATS was 0.994 and for MT 0.982. CONCLUSIONS: In patients with histological diagnosis of NSP both VATS and MT showed similar and excellent results of false negative cases and negative predictive value in excluding malignant pleural disease.

First Characterization with Ultrasound Contrast Agent of a Fibrovascular Polyp Before Its Endoscopic Resection: A Case Report (with Videos).

We described for the first time the contrast enhancement of a giant fibrovascular esophageal polyp using ultrasound contrast agent, Sonovue® (Bracco, Milan, Italy) during echoendoscopy. Fine Doppler was unsuccessful in showing vascularization due to the mobile characteristic of the tumor. In contrast, via Sonovue® , tissue microcirculation was highlighted inside the entire head of the polyp, leading to better appreciate the risk of bleeding related to its resection. In a second part, we showed the feasibility of classic polypectomy for this giant polyp (5×5 cm) without complication and results of control endoscopy at 3 months. The present case is summarized in a video.

Non-specific pleuritis: pathological patterns in benign pleuritis.

A pleural biopsy without granulomatous inflammation or tumour cells is interpreted as 'non-specific pleuritis' (NSP), a diagnosis without any specificity, often frustrating for physicians. However, varying histological features are found in NSPs with unknown significance. The aim of this study was to describe the detailed microscopic features of NSP and correlate them with the underlying aetiology. One hundred patients diagnosed with NSP after pleural biopsy were retrospectively evaluated. A benign cause of pleural effusion was attributed. Histological features evaluated were inflammation, fibrosis, vascular proliferation, haemorrhage, fibrin, oedema and mesothelial hyperplasia. A semi-quantitative scoring was applied. Bacterial-caused and autoimmune disease-associated NSPs showed a higher score followed by viral and drug-induced conditions, while pneumothorax and cardiac-induced NSPs showed a lower score (p<0.0001). The degree of fibrosis was higher in bacterial NSP, and the type of fibrosis was cellular in this group (p=0.006). Vascular proliferation differed between groups (p<0.0001), and was higher in bacterial NSP. Histological findings differ significantly between the varying aetiologies of NSP, and this may be used to suggest the cause of the effusion.