Background Cytological analysis is part of the initial etiological evaluation of serous effusions. The newly proposed International System for Reporting Serous Fluid Cytopathology (ISRSFC) aims to standardize reporting. Methods All pleural and peritoneal effusion samples admitted for cytological analysis at our institution between 2012 and 2016, and pericardial effusion samples admitted between 2008 and 2018, were reviewed and reclassified according to the ISRSFC. Risk of malignancy (ROM) and performance parameters were calculated. Results 1496 pleural effusion samples were reclassified: 12(0.8%) non‐diagnostic (ND), 944(63.1%) negative for malignancy (NFM), 9(0.6%) atypia of undetermined significance (AUS), 54(3.6%) suspicious of malignancy (SFM) and 477(31.9%) malignant (M). 64 pericardial effusion samples were reclassified: 23(35.9%) NFM, 1(1.6%) AUS, 4(6.3%) SFM and 36(56.2%) M. 763 peritoneal effusion samples were reclassified: 5(0.7%) ND, 457(59.9%) NFM, 12(1.6%) AUS, 37(4.8%) SFM and 252(33%) M. The ROM was, respectively, for each of the aforementioned categories, 57.1%, 23.9%, 50%, 76.2%, 100% in pleural effusions, 100%, 26.3%, 62.5%, 91.7%, 100% in peritoneal effusions and 0% for NFM, 0% for AUS and 100% for M in pericardial effusions. Sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy were, respectively, 61.6%, 100%, 100%, 73.3%, 81.3% for pleural, 100%, 100%, 100%, 100%, 100% for pericardial and 61.2%, 100%, 100%, 70%, 79.7% for peritoneal effusion samples. Conclusion Serous effusion cytology has a high specificity and positive predictive value and a modest sensitivity and negative predictive value, supporting its role in confirming the diagnosis of malignancy. The ISRSFC will increase standardization and reproducibility in reporting, leading to improved clinical decision‐making.

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Background: trastuzumab is considered the standard of care for human epidermal growth factor receptor-2 (HER-2+) breast cancer patients. Regardless of the benefits of its use, many early-stage patients eventually recur, and usually, the disease progresses within a year. Since about half of the HER-2+ patients do not respond to trastuzumab, new biomarkers of prognosis and prediction are warranted to allow a better patient stratification. Annexin A1 (ANXA1) was previously reported to contribute to trastuzumab resistance through AKT activation. An association between adenine thymine-rich interactive domain 1A (ARID1A) loss and ANXA1 upregulation was also previously suggested by others. Methods: in this study, we examined tissue samples from 215 HER-2+ breast cancer patients to investigate the value of ARID1A and ANXA1 protein levels in trastuzumab response prediction and patient outcome. Expression of ARID1A and ANXA1 were assessed by immunohistochemistry. Results: contrary to what was expected, no inverse association was found between ARID1A and ANXA1 expression. HER-2+ (non-luminal) tumours displayed higher ANXA1 expression than luminal B-like (HER-2+) tumours. Concerning trastuzumab resistance, ARID1A and ANXA1 proteins did not demonstrate predictive value as biomarkers. Nevertheless, an association was depicted between ANXA1 expression and breast cancer mortality and relapse. Conclusions: overall, our results suggest that ANXA1 may be a useful prognostic marker in HER-2+ patients. Additionally, its ability to discriminate between HER-2+ (non-luminal) and luminal B-like (HER-2+) patients might assist in patient stratification regarding treatment strategy.