ECP 2023 Abstracts

S18 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 the additionally stained biopsies from an adult was also positive for HEV RNA by RNA-FISH and IF. Focal IF positivity for HEV peptide was observed in eight allografts. Ribavirin therapy was not successful in paediatric index patient: after a relapse of HEV infection rivavirin is still administered. In the second patient successful elimination of HEV was achieved after short-course ribavirin therapy. Conclusion: HEV infection is an important differential diagnosis for T-cell rejection within transplanted kidneys, but detailed data on inci- dence are missing. Immunostaining of HEV peptide does not neces- sarily prove acute infection of renal tissues since RNA-FISH for HEV was positive only in two of the ten cases with positive tubular epithelial staining for HEV peptide by immunofluorescence. RNA-FISH seems to be a reliable and quick method to localize HEV and requires only a small amount of tissue. OFP-04-014 Caveolin-1 expression in glomerular and peritubular capillaries as diagnostic support for doubtful cases of kidney rejection: a proof of concept M. Carroli*, S. Chillotti, D. Malvi, E. Albertini, B. Fabbrizio, A. D’Errico, G. Pasquinelli, F. Vasuri *Pathology Unit, IRCCS Azienda Ospedaliero-Universitaria di Bolo- gna, Bologna, Italy., School of Anatomic Pathology, Department of Biomedical and Neuromotor Sciences, University of Bologna, Italy Background & objectives: Caveolin-1 has been described as a useful immunohistochemical marker of antibody-mediated rejec- tion after kidney transplantation. Aim of the present study was to evaluate the diagnostic utility of Caveolin-1 in borderline cases, i.e., with doubtful morphology between antibody-mediated and T-cell-mediated rejection. Methods: Thirty-nine renal biopsies were evaluated, 14 post-reperfu- sion biopsies (controls), 15 histologically-proven rejections (6 T-cell- mediated and 9 antibody-mediated), and 10 morphological borderline rejection cases. Histology was revised, and immunohistochemistry (IHC) for Caveolin-1 and C4d was automatically performed. Caveo- lin-1 expression was semi-quantitatively assessed as the percentage of positive glomeruli and the density of positive peritubular capillaries/ mm2. Results: In the T-cell-mediated rejections (TCMR) and antibody- mediated rejection (AMR) groups, the mean percentage of Caveo- lin-1-positive glomerular capillaries was 0.0%, and 70.0%±34.2% respectively, meaning that no positive glomeruli were observed among TCMR (p<0.001). The mean density of peritubular capillaries/mm2 was 5.2±3.1 and 21.2±22.1, showing the highest value in AMR group (p=0.019). In the 10 borderline cases the mean percentage of posi- tive glomeruli was 21.9±25.1% and the mean density of peritubular capillaries was 12.5±8.2/mm2; however, 4 had completely negative glomeruli, 2 less than 30% positive glomeruli and 4 more than 30% positive glomeruli, suggesting a different immunological pathogenesis for the borderline group. Notably, no correlation between Caveolin-1 and C4d was observed. Conclusion: Our results confirm that Caveolin-1 immunohistochemis- try is a valid tool in diagnosing AMR, even when C4d is not determi- nant. In particular, Caveolin-1 expression in more than 30% of glomer- uli distinguishes AMR, while TCMR cases show no positive glomeruli. Most important, in those borderline cases in which the rejection has not a clear histological classification, an alleged role of Caveolin-1 IHC is suggested by the fact that some of them are strongly positive, while others are completely negative. OFP-04-015 Modified method of histological scoring and grading of renal amy- loidosis correlates with renal outcome: an Indian experience V. Agrawal*, I. Singh, R. Pandey, M. Jain, N. Prasad, A. Kaul *SGPGIMS, India Background & objectives: Renal amyloidosis is usually associated with poor renal outcome. We studied the typing of amyloid and the extent of amyloid deposition in renal biopsies and correlated it with the clinical presentation and renal outcome. Methods: Renal biopsies diagnosed as renal amyloidosis over a period of ten years were reviewed. Amyloid typing was done using a multimo- dality approach including clinical history, bone marrow examination, tests for monoclonal proteins, renal tissue immunofluorescence and immunohistochemistry. Renal amyloid deposits were scored and graded by a slight modification of the previously described method (Şen S and Sarsik B (2010). Results: The study included 147 patients diagnosed as amyloidosis on renal biopsy, with M:F ratio of 2.3:1 and mean age 51.3±14.5years. 24-hour proteinuria was 6.6 ± 4.7gm/day (range 0.146-35gm/day). Renal failure was present in one-third at diagnosis. Glomerular pat- tern of involvement was diffuse mesangio-capillary in 77% biopsies. AA (58.8%) type was commonest, followed by AL (38.7%; AL- lambda-96%). On Renal Amyloid Prognostic Score (RAPS) scoring, two-third of the biopsies showed advanced stage (grade 3). 50 patients died due to disease (average 6.2months; range 0.1-30.5 months). The factors associated with a poor outcome were serum creatinine, cardio- myopathy, degree of IFTA on histology, high RAPS score and grade and AL amyloidosis. Conclusion: We found AA to be the most common type of renal amy- loidosis and most of our patients were diagnosed at an advanced stage of renal amyloidosis. We describe a modified histopathological scoring and grading system for renal amyloidosis which shows correlation with clinical presentation at diagnosis and with overall survival. OFP-05 | Oral Free Paper Session Pulmonary Pathology OFP-05-001 A single centre re-evaluation of the correlation of pleural fluid cytology and pleural biopsies in malignant mesothelioma and investigation of inter-observer variability G. Raghuram*, A. Loona, I. Soomro *Nottingham University Hospitals NHS, United Kingdom Background & objectives: The RCPath dataset sets a positive predic- tive value (PPV) of 50% for the diagnosis of malignant mesothelioma in cytology. Previous auditing within our institution showed a PPV of 53%. Here, we re-evaluate this and investigate inter-observer variability in cytology reporting. Methods: A search was conducted on our laboratory information system ‘WinPath’ to find cases of mesothelioma reported between 2016 to 2021. Clinicopathological information from the histology reports was collated including dates between cytology and biopsy sampling. Cases where there was a diagnosis of mesothelioma on biopsy but a negative cytology report were reassessed by two expe- rienced pathologists. Results: Of 179 cases, 129 had both cytology and biopsy specimens and PPV was 55.5%. Rarer histological subtypes; desmoplastic, lymphohis- tiocytoid and well differentiated papillary mesothelioma were associated with negative cytology results. One case of ‘Mesothelioma-in-situ’ was seen for which the cytology specimen was reported as atypia (not other- wise specified). Of 50 cases originally reported as negative cytology, 7 (14%) were upgraded, 24 (48%) remained negative and in 15 (30%) there was differing opinions between the two pathologists. Immunohistochem- istry was primarily used as an adjunct for malignant effusions to deter- mine cell phenotype, with no cases being sent for molecular analysis. The average delay between a cytology and biopsy specimen was 13 days. Conclusion: Despite increased awareness of pitfalls of cytology, PPV of pleural fluid cytology appears to inherently be approximately 50%.