ECP 2023 Abstracts

S386 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 E-PS-24-075 Immunohistochemical analysis of EGFR, HER2/NEU, ERK and phosphorylated ERK expression in prostatic adenocarcinoma with clinicopathological correlation A. Shalaby*, H. Mahmoud, S. Al Sinawi, S.A. Saad El-Din *Oman Background & objectives: The alterations of EGFR, HER2/neu and RAS/RAF/MEK/ERK signalling are important in carcinogen- esis. Their activation in prostate cancer is not fully addressed. we aimed to assess expression of EGFR, HER2-neu, and ERK) in pros- tatic adenocarcinomas and to correlate with the clinicopathological parameters. Methods: Immunohistochemistry using tissue microarrays was done for EGFR, HER2/neu, inactive, and phosphor-ERK was performed on tissues from 166 patients. Markers expression and correlation with the clinicopathologic parameters were analysed statistically. Results: Expression of EGFR, HER2 neu, phosphorylated and inactive ERK was seen in 8.4%, 1.4%, 78.2%, and 83.4% respectively whether low (patchy) or high expression (diffuse). No significant correlations were found between patient criteria and expression of the four studied markers. The negative expression of inactive ERK and EGFR was sig- nificantly correlated to the high tumour stage with p values 0.03 and 0.01 respectively. Conclusion: EGFR and HER2neu may play a limited role in prostatic adenocarcinoma in view of their expression in a small number of cases. The expression of inactive ERK and phosphorylated ERK was appreciated in most cases. Thus, we suggest that EGFR inhibitors may have a limited role in the treatment of castrate-resistant prostate cancer patients, but MEK/ERK inhibitors may be more promising as a targeted therapy, further molecular studies are needed to investigate the exact mechanism and significance of their expression. E-PS-24-076 Renal cell carcinoma, unclassifed (high grade oncocytic) with MSH6 mutation - a case report R. Shi*, C.Y. Chow, T.K.Y. Tay, L.Y. Khor *Singapore General Hospital, Department of Anatomical Pathology, Singapore Background & objectives: Renal cell carcinoma (RCC), unclassified represents a group of RCC cannot be classified into any established subtypes. They have heterogenous pathological features and usually aggressive clinical course. Methods: Herein, we report a case of 78 year old male, presented as an incidental finding of a 12cm left kidney tumour during the work-up of loss of weight. Results: On the histology of radical nephrectomy specimen, the tumour showed exclusive high grade oncocytic morphology with extensive extra- renal extension. The next generation sequencing revealed no known molecularly defined RCC related gene mutation, but a single nucleotide variation of MSH6 gene. The immunohistochemistry staining showed possible subclonal staining patter of MSH6 protein. The patient has been referred to subsequent genetic counselling to rule out Lynch Syndrome. Conclusion: As MSH6 gene mutation has not been well reported in RCC, unclassified. Our case may contribute a new insight into this group of tumour. E-PS-24-078 A case report: cystadenoma of the rete testis S. Stifter-Vretenar*, E.B. Hansen *Aarhus University Hospital, Denmark Background & objectives: A finding of cystadenoma in the rete testis is presented. This rare entity can represent a diagnostic pitfall in small testicular cystic lesions since there are far more common conditions such as epididymal cysts, tubular ectasy, or rete hyperplasia. Methods: A 69 old man was admitted to the urology clinic with a pain- less mass symptom in the left scrotal region. The sonography evalua- tion revealed a complex partially extra-testicular overall mediastinum located mass measuring 2.5x3 cm. Clinically was process diagnosed as a multicystic spermatocele. Consequently, was the patient subjected to a left-sided orchidectomy, and the specimen was submitted for patho- histological evaluation. Results: Pathologic examination revealed a macroscopically incon- spicuous collapsed, multiseptated cystic process consistent with a pre- dominantly rete testis origin. Some of the peripherally extra-testicular located cystic spaces had small accumulations of spermatids with a small proportion of venous space appearing congested. The lesion mostly comprised thin-walled fibrous stroma-derivated septated empty cystic space with bland cubic cell epithelial lining and occasional small foci of proliferating, budding, and tufting cells with minimal atypia. The lesion was immunohistochemically AE1/3 and EMA positive. A proliferation rate Ki67 determined was low. Microscopic appearance and localization of the lesion supported with immunohistochemical analysis (IHC) confirmed the diagnosis of cystad- enoma together with a small spermatocele laying peripheral to tumour. Conclusion: The rete testis cystadenoma is a rare finding. The impor- tance of noting it is in gaining additional information on tumour devel- opmental biology. Furthermore, since benign tumours of the rete tes- tis are rare entities, they can be easily overlooked and misdiagnosed when presented in an initial stage. Therefore, we think this entity is of merit for presentation and should draw our attention since it is one of the differential diagnoses of the multicystic process of the testis and scrotal region. E-PS-24-079 Diagnostic role and prognostic impact of PSAP immunohistochem- istry: a tissue microarray study on 31,358 cancer tissues from 127 different tumour types L. Tribian*, M. Lennartz, N. Blessin, S. Kind, F. Viehweger, C. Hube- Magg, A. Menz, R. Uhlig, E. Burandt, G. Sauter, R. Simon, M. Kluth, S. Steurer, T.S. Clauditz, C. Bernreuther *Institute of Pathology, University Medical Center Hamburg-Eppen- dorf, Germany Background & objectives: Prostatic specific acid phosphatase (PSAP) protein is produced in prostate epithelial cells and it is used as an immuno- histochemical marker for prostate cancer. However, studies have reported PSAP expression to occur in various other tumour entities as well. Methods: To assess the level of specificity of PSAP expression for prostate cancer and to evaluate the prognostic impact of reduced PSAP expression in prostate cancer, 14,137 tumour samples from 127 differ- ent tumour (sub)types, 17,747 prostate cancers, and 8 samples each of 76 different normal tissue types were analysed by immunohistochem- istry in a tissue microarray format (TMA). Results: In prostate cancer, PSAP staining was seen in 100% of Glea- son 3+3, 95.5% Gleason 4+4, 93.8% recurrent prostate cancer under androgen deprivation therapy, 91.0% Gleason 5+5 and 31.2% small cell neuroendocrine prostate cancer. Reduced PSAP staining was strongly linked to high pT stage, high Gleason grade, lymph node metasta- sis, early PSA-recurrence (p<0.0001 each),high androgen receptor expression and TMPRSS2:ERG fusions. In multivariate analyses, low