Correction to: 34th European Congress of Pathology – Abstracts

Background & objectives: Rectal tumours developed in low and middle rectum require neo-adjuvant chemo-radi-otherapy followed by surgical resection. The therapeutic response can be estimated following several therapeutic effect evaluation systems. Our study aims to correlate different therapeutic effect clas-sifications and evaluate their reproducibility. Methods: 100 rectal tumour resections after neoadjuvant were interpreted by three different pathologists. The therapeutic effect was estimated by the following classification system: RCG, m-RCG, TRG, RCpath, and Dvorak. Statistic measurements were established using SPSS soft-ware in order to evaluate the concordance of different classification systems, their reproducibility, and their correlation with patient survival. Results: The concordance between different pathologists in the evaluation of the therapeutic effect using different systems was low to medium (kappa: 0,3-0,6). Overall survival (OS) was 71,55% with a medium duration of 46 months. The progression-free survival (PFS) was 62,94% trans-urethral resections and post-chemotherapy pelvectomy. Cytological of the for reporting urinary cytopathology after centrifugation and Papanicolaou Background & objectives: Molecular aberrations in renal cell cacinomas (RCC) got different diagnostic value and for some a prognostic and therapeutic implications. Our study aims to evaluate the diagnostic and prognostic utility of fluorescence in-situ hybridization (FISH) in the care management of RCC. Methods: We included prospectively cases of RCC diagnosed after histological examination and immunohistochemistry analysis for some cases. The methodology consisted in highlighting by FISH molecular abnormalities for each histological subtypes using Zytolight® probes. Probes were chosen depending on the histological diagnosis and their corresponding molecular abnormalities. Results: 25 case of RCC were included. Clear-cell carcinoma (ccRCC) represented 48% by papillary RCC (pRCC) chromophobe with 2 cell carcinoma papillary one of oncocytoma tubulo-cystic tcRCC

survival (OS) was 71,55% with a medium duration of 46 months. The progression-free survival (PFS) was 62,94% with a medium duration 38,46months. The most correlated classification system with OS was mRCRG (mRCRG1: 72,58%; mRCRG2: 71,95%; mRCRG3: 40,77%). The other Classification systems didn'a t show statistically significant correlation with the OS. The PFS was correlated with TRG (TRG1:74,35%; TRG2:51,71%; TRG3:40,08%; TRG4:76,64%; TRG5:48,08%). The other Classification systems didn't show a statistically significant correlation with the PFS. Conclusion: Most therapeutic evaluation systems didn't show a significant correlation with the OS and the PFS. This, create the necessity to develop a new classification system with more accuracy and prognostic value by the consideration of other parameters such as lymph nodes' therapeutic effect and the macroscopic feature.

E-PS-22-008
Osteosarcomatous dedifferentiation of leiomyosarcoma: a case report R. Ben Tayeb*, L. El Moutaoukkil, I. Gerard, K. Abdellaoui, S. Ait Brahim, L. Tahiri El Ousrouti, S. Arifi, L. Chbani *Pathology department, University hospital hassan II, Morocco Background & objectives: Dedifferentiation of leiomyosarcomas is an extremely rare phenomenon. This morphological transformation may be into several heterologous components with a loss of expression of muscular immunohistochemical markers. This communication aims to report a case of a dedifferentiated leiomyosarcoma with osteosarcomatous component. Methods: 43 years old-women presented a local recurrentsubcutaneouss mass of the left thigh for the third time after chemo-radiotherapy and surgical resection. The histologic diagnosis of the anterior resections was leiomyosarcoma The online version of the original article can be found at https:// doi. org/ 10. 1007/ s00428-022-03379-4 with immunohistochemical proof (expression of SMA, H-caldesmon and Desmin). The morphological examination of the actual mass shows an osteosarcomatous feature with no expression of H-caldesmon and Desmin. Results: This histological metamorphosis make the diagnosis difficult especially if there is a loss of expression of muscular markers with no anterior histo-immunohistochemical proof of leiomyosarcoma. The simultaneous presence of a well-differentiated leiomyosarcoma make the diagnosis less difficult. The differential diagnosis with other sarcomas is not always easy. The diagnostic approach should be in concertation with radiologists and must exclude other possible diagnosis before confirming the diagnosis. In our case, the diagnosis of soft tissue osteosarcoma could be wrongly suggested but fortunately the anterior diagnosis of leiomyosarcoma allowed us to make the correct diagnosis of dedifferentiated leiomyosarcoma. This transformation is possibly due to multiple reprogramming genetic changes associated with tumoral recurrence. Conclusion: Dedifferentiated leiomyosarcoma is a challenging diagnosis because of its rarity and its differential diagnosis problems with other sarcomas. Immunohistochemistry is not always able to solve the problem since this dedifferentiation can be associated with the loss of expression of muscular markers. Background & objectives: The urine cytology can be useful in the follow-up of patients after tumour resection and the screening of population with high-risk of bladder cancer. Our study aims to evaluate the correlation between urine cytology and histology. Methods: We included prospectively cases of bladder cancer. Urines for cytological examination were collected directly before the surgical intervention. Tumour specimens for histological analysis were trans-urethral resections and postchemotherapy anterior pelvectomy. Cytological samples were interpreted basing of the Paris system for reporting urinary cytopathology after centrifugation and Papanicolaou coloration. Results: We collected a total of 12 cases with a cytology specimen and histologic sample for each case. The mean age is 65yr (29yr-85yr). Sex ratio: 11/1 (M/F). 11 specimens (91,66%) were trans-urethral resections and one case (8,33%) of post-chemotherapy anterior pelvectomy. 3 transurethral resections and the post-chemotherapy anterior pelvectomy (33,3%) didn't show any tumour cells. One case (8,33%) was diagnosed as papillary urothelial neoplasm with low malignant potential, 3 trans-urethral resections (25%) as low-grade urothelial carcinoma and the remaining 4 cases (33,3%) as high-grade urothelial carcinoma. Cytologic categories were correlated to their corresponding histologic feature.

Conclusion:
The urine cytology is a non-invasive test that can be used in the follow-up of patients or in the screening of bladder cancer since it has a good correlation with histology with a high predictive value as shown in our study.

E-PS-MD-01-005
Dedifferentiated gastrointestinal stromal tumour after treatment with imatinib and review of litterature R. Ben Tayeb*, L. El Moutaoukkil, K. Abdellaoui, S. Ait Brahim, S. Arifi, L. Tahiri El Ousrouti, L. Chbani *Pathology department, University hospital hassan II, Morocco Background & objectives: Dedifferentiation of gastrointestinal stromal tumours (GIST) is a rare process of transformation to an unusual histologic and immunhistochemical feature. This process can occur either de-novo or after Imatinib treatment. This communication aims to report a case of a dedifferentiated GIST. Methods: 57-years-old male patient presented gastric tumour of 11cm. Biopsy showed a spindle-cell feature, CD117-positive and DOG1-positive. Sanger-sequencing highlighted mutation of exon11 of KIT-gene (p.Q549_ W557del). The gastrectomy after Imatinib treatment showed pleomorphic proliferation with rhabdoid cells, CD117-negative and DOG1-negative. Sanger sequencing showed the same mutation of KIT-gene found in the first biopsy confirming the diagnosis of a dedifferentiated GIST. Results: The phenomenon of dedifferentiation of GISTs presents a diagnostic pitfall especially in de novo situations with the loss of expression of CD117 and DOG1. In our case, the anterior biopsy with a histologic and immunohistochemical diagnosis of GIST allowed us to suggest the diagnosis of dedifferentiated GIST. The Sanger sequencing confirmed the diagnostic by highlighting the same mutation detected in the initial biopsy. Until now, only 13 papers are published in the literature, describing 27 cases of dedifferentiated GISTs. Two third of cases are post-therapeutic dedifferentiated GISTs. In all cases, sequencing was the final tool of diagnostic. Conclusion: GISTs are usually identified based on their morphology and immunohistochemical profile. However, dedifferentiation with altered morphology and loss of CD117 and DOG1 expression can make the diagnosis difficult. Molecular tests resolve the problem by detecting genetic abnormalities usually described in GISTs. Our study aims to evaluate the diagnostic and prognostic utility of fluorescence in-situ hybridization (FISH) in the care management of RCC. Methods: We included prospectively cases of RCC diagnosed after histological examination and immunohistochemistry analysis for some cases. The methodology consisted in highlighting by FISH molecular abnormalities for each histological subtypes using Zytolight® probes. Probes were chosen depending on the histological diagnosis and their corresponding molecular abnormalities.

E-PS-MD-01-006
Results: 25 case of RCC were included. Clear-cell carcinoma (ccRCC) represented 48% followed by papillary RCC (pRCC) with 24%, chromophobe RCC (chRCC) with 12%, 2 cases (8%) with uncertain diagnosis clear cell carcinoma or papillary carcinoma and one case of renal oncocytoma (RO) (4%), tubulocystic RCC tcRCC (4%). The FISH method supported the morphological diagnosis in all cases except in one biopsy diagnosed histologically as ccRCC and FISH allowed the diagnosis correction to a pRCC by the detection of a polysomy of chromosome 17 described in this histological subtype. FISH can also be used in prognostic categorisation of patients by the detection of the loss of CDKN2a-gene which predict worse prognosis. Conclusion: FISH method got an implication in the diagnostic approach of RCC especially in cases with non-conclusive histology and immunohistochemistry. It can also be used in the prognosis of this tumour in addition to other histo-prognostic factors. This method will lead to more precision in diagnosis and better care management personalisation in RCC.