ECP 2023 Abstracts

S158 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 *Pathology Department, Portuguese Oncology Institute of Porto (IPO- Porto), Portugal Background & objectives: Recent approval of trastuzumab derux- tecan in previously treated HER2-low advanced breast cancers intro- duces new challenges and needs in HER2 evaluation. Our goal is to optimize HER2 testing in clinical practice by means of a Portuguese national consensus-based guideline recommendations. Methods: A 3-round modified Delphi exercise was conducted. The Scientific Committee (SC), composed of 6 pathologists, performed an exhaustive bibliographic search, and discussed the most relevant aspects related to the implementation of HER2-low evaluation into clinical practice. After that, the SC defined and validated the statements to be included in the Delphi questionnaire. Results: Questionnaire is composed of 5 topics, each with several statements: (i) scientific evidence that supports clinical needs; (ii) technological capacitation; (iii) technical and analytical process and quality control; (iv) HER2 testing algorithm and interpretation; (v) structure of the anatomopathological report. The panel of experts selected by the SC comprises pathologists and cli- nicians with relevant experience in breast cancer. Each expert received the Delphi questionnaire (2 rounds) and were asked to express their degree of agreement with each statement, on a 5-point Likert scale. Data analysis and stability analysis was assessed and the percentual variation of the proportion of concordance between rounds was used as an indicator of convergence. Conclusion: With the methodology outlined in this project, consensus is expected to be gathered regarding the following topics: (i) scientific evidence that supports clinical needs; (iii) technical and analytical process and quality control; (iv) HER2 testing algorithm and inter- pretation. We expect further discussion related to (v) structure of the anatomopathological report to establish a consensus. This work had financial support of AstraZeneca Portugal. E-PS-02-022 Spontaneous regression of breast carcinoma. Presentation of three cases with immunohistochemical study of TILs A. Córdoba*, R. Beloqui, I. Amat, I. Fernandez, M.R. Mercado, C. Cerezo, D. Guerrero-Setas *Hospital Universitario de Navarra, Spain Background & objectives: Spontaneous tumour regression (SR) is defined as the partial or complete disappearance of a tumour in the absence of treatment capable of causing regression. Few isolated cases have been published yet. We present three cases of breast cancer with SR. Methods: The studied cases are three women aged 78, 79 and 68 year-old who radiologically showed nodules of 27, 30 and 24 mm, respectively. Core needle biopsy was performed in all cases. The tumours were infiltrating BC, grades 2 and 3 (2 cases), with luminal A (one case) and triple-negative (two cases) phenotype. We studied TILs in the tumour bed. Results: After diagnosis, conservative surgery with sentinel lymph node was performed with a maximum interval of 1-month. The resec- tion specimen showed minimal residual tumour of 1.2 and 1.5 mm (30 cells) or no tumour remnants (one case). Total inclusion was performed. In one case an intense inflammatory reaction, partly granulomatous, was observed. In another case, extensive coagulation necrosis and abundant lymphoid infiltrate was present, whereas a very dense lym- phoid stroma was observed in the third case. The TILs were composed by lymphocytes T/B = 85/15%; CD4/CD8 =30/70; and TIA-1= 40%. The population of macrophages was pre- sent as CD163+ in 30% of the infiltrate. Sentinel lymph nodes were negative. Conclusion: SR in breast cancer is a rare event recognized in the medical literature and remains an unexpected phenomenon. Due to the rarity of SR, case studies preclude sufficient data on its biological behaviour and clinical significance. Possible mechanisms underlying spontaneous cancer regression include hormonal or immune system mediation, inhibition of angiogenesis, psychological factors, trauma, infection and epigenetic mechanisms. The presence of abundant inflammatory infiltration in all three cases may suggest recruitment of the host immune system. E-PS-02-023 Syringomatous tumour: case report A. Das Cerci*, T. Toyran, M. Ergin, S. Zorludemir *Cukurova University Faculty of Medicine, Department of Pathology, Adana, Turkey Background & objectives: It is expected that the findings in study will contribute to raising awareness about the rare Syringomatous tumour, which can result in unnecessary surgical procedures due to misdiag- nosis. We aim to discuss a 40-year-old female patient diagnosed with Syringomatous tumour. Methods: The blocks of a patient who was diagnosed with malignancy in the outer centre as a result of the biopsy were brought to our hospital for consultation. Sections were taken. Stained with hematoxylin eosin and immunohistochemistry stains. Results: Microscopically, ductular structures lined by 2 rows of epithe- lium and surrounded by myxoid fibrous stroma were observed, infiltrat- ing smooth muscle bundles, around lactiferous ducts in places. Some ducts had ovoid shapes with comma-like extensions. These structures showed keratinized cysts and varying degrees of squamous metaplasia. PAS(+) secretory material was prominent in the cyst lumens. There were no significant atypia, mitoses, or necrosis. There was also no lymphovascular or perineural invasion. Cells located at the periph- ery showed positive staining with HMWK, CK14, P63, and CD10 on immunohistochemistry. The Ki67 proliferation index was determined as 5%. Conclusion: First described by Rosen in 1983, Syringomatous tumour is a rare benign tumour that often mimics malignancy in clinical and histomorphological features. Less than 80 cases have been reported in the literature for this tumour. Therefore, it is important to keep in mind to avoid misdiagnosis and unnecessary surgical procedures for this rare tumour. In this study, we aim to discuss a 40-year-old female patient diagnosed with Syringomatous tumour, highlighting its significance. Funding: Cukurova University E-PS-02-024 Benign Müllerian inclusion in the axillary lymph node of a patient with breast carcinoma: a case report S.K. Dursun*, T. Soylemez Akkurt *Basaksehir Cam and Sakura City Hospital, Turkey Background & objectives: Benign inclusions, such as capsular nevi, epithelial cysts, and heterotopic mammary glands, are common in axil- lary lymph nodes. Benign Müllerian inclusions are frequently seen in pelvic/para-aortic lymph-nodes but only rare reports have described involvement of lymph nodes above the diaphragm. Methods: A 39-years old woman presented to our hospital with breast mass. On physical examination, a rigid, solid lesion was present at the superior outer quadrant. A lesion with suspicious malignancy (28x18 mm) was detected on mammography. Core biopsy was performed and the diagnosis was luminal A mammary carcinoma. Thus, the patient underwent breast-sparing surgery with sentinel lymph node (SLN) biopsy. Results: Two SLN were submitted for frozen sections. No metastatic carcinoma was present in frozen section slide. Histopathological examination revealed invasive carcinoma with mixed ductal and lobular