ECP 2023 Abstracts

S166 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 Methods: A retrospective analysis of 29 fibroepithelial lesions of the breast (FELB) diagnosed by core needle biopsy (CNB) who underwent surgical excision, in an oncological hospital, from 2019 to 2023. CNB were revised. Results: Of the 29 CNB’s, 26 were accurate: 16 fibroadenomas (FA), 4 cellular FELB, 3 unclassified FELB, 1 borderline phyllodes tumour (PT), 1 benign spindle cell lesion and 1 biopsy with minor changes. There was 96% of agreement with the definite histological diagnosis and 1 case was upgraded from FA to benign PT. There were 3 inac- curate CNB, all of them FELB initially diagnosed as FA. There was 100% agreement with the definite histological diagnosis: 1 benign PT and 2 borderline PT. Conclusion: The present study suggests that FELB diagnosis in CNB has a high coherency with the histological diagnosis of surgical speci- mens, being the upgrade rate 3%. The intrinsic limitation of CNB and heterogeneity of FELB may explain the upgrading. The pitfalls in CNB were mainly due to core fragmentation and the cellularity of the stro- mal component. The CNB diagnosis accuracy of FELB and a triple multidisciplinary approach dictate the patient’s clinical management. E-PS-02-054 Morphological stability of HER-2 expression before and after breast carcinoma neoadjuvant chemotherapy O. Reshetnikova*, L. Rudiuk, A. Musatov *Immanuel Kant Baltic Federal University, Russia Background & objectives: Human epidermal growth factor receptor-2 (HER-2) protein expression level in breast cancer (BC) is a valuable prognostic marker. The evaluation of its parameters may help in per- sonalized handling of BC diagnostics and treatment strategies. Methods: Clinical behaviour, pathological efficacy, HER-2 protein expression were evaluated in eighty cases of BC before and after neo- adjuvant chemotherapy (NAC). Nine cases after pathological complete response to NAC were excluded from further investigations. The degree of HER-2 receptor expression (DAKO, Polyclonal, 1:600) was evalu- ated by immunohistochemistry and in cases of equivocal expression by FISH according to ASCO/CAP guidelines. Results: The results have shown that HER-2 receptor expression did not change after NAC in 40 cases (56.3%). An increase in HER-2 receptor expression was recorded in 19 cases (26.8%), including three residual tumours that changed to HER-2 positive status after treatment. Decreased expression levels were observed in 12 cases (16.9%) of breast cancer. There was no complete loss of HER-2 expression (0) in this study. Conclusion: NAC changes the status of HER-2 receptors mainly towards increased expression. The obtained results show the need to study the HER-2 status of the residual tumour for an adequate selection of adjuvant therapy. The importance of further studies of the heteroge- neity of HER-2 expression in personalized diagnostics and treatment of patients with BC has been discussed. E-PS-02-055 Breast carcinoma immunophenotype features after neoadjuvant therapy O. Reshetnikova*, L. Rudiuk, A. Musatov *Immanuel Kant Baltic Federal University, Russia Background & objectives: The sensitivity of certain histological types of breast cancer (BC) to molecular targeted drugs has now been estab- lished. Neoadjuvant chemotherapy (NAC) aims to achieve a morpho- logical response for the treatment. This investigation evaluates the BC immunophenotype changes after NAC. Methods: Eighty women with BC underwent NAC followed by sur- gery. Their medical documents were studied. The grade of tumour was determined according to the Nottingham Histologic Score. IHC studies were performed on a Leica BOND MAX immunoassay using ER, PgR, HER2, and Ki67 antibodies. Nine cases after pathological complete response to NAC were excluded from further investigations. Results: The study has shown that molecular phenotypes of the BC after prescribed NAC have changed in 29 cases (36.3%) of patho- logical examination. There were variable patterns of surrogate type change. In 44.8% there was a change from luminal B HER2-negative to luminal type A. Slightly less frequently, in 13.8%, triple negative changed to luminal B HER2-negative after NAC treatment. In single cases, changes between other molecular subtypes of breast cancer were observed. Conclusion: Present investigation revealed significant differences in pathology and immunophenotype of the BC and its heterogene- ous response to NAC. Various clinical behaviour and morphological features of the studied neoplasm create a challenge for managing BC patients. An analysis of the study results confirmed the need for further research in molecular heterogeneity of BC and possible responses to targeted therapy. Identifying new markers in BC for pathologic diag- nostics and NAC targets should be supported. E-PS-02-056 Variations in steroid hormone receptor status after breast carci- noma neoadjuvant chemotherapy O. Reshetnikova*, L. Rudiuk, A. Musatov *Immanuel Kant Baltic Federal University, Russia Background & objectives: Neoadjuvant chemotherapy (NAC) of the breast cancer (BC) causes alterations in clinical behaviour, morphological and immunohistochemical characteristics of the primary tumour. Changes in steroid hormone receptor expression character have an effect on disease prognosis and postoperative chemotherapy treatment guideline. Methods: Eighty cases of BC before and after standard courses of NAC were examined. Histological examination was performed in standard- ized hematoxylin and eosin staining with determination of tumour’s grade. IHC examination was performed on a Leica BOND MAX immu- nostainer using monoclonal antibodies ER, PgR. The degree of ER and PR expression was assessed using the Allred score system. Results: Our study revealed that after neoadjuvant therapy ER and PR expression remained stable in most observations (35 cases, 49.3%, and 31 cases, 43.7%, respectively). Steroid hormone receptor conversion was detected in 22 cases (31.0%). Complete loss of ER expression discovered in 9.0% and PR - in 32.0% of observations. Combined loss of ER and PR detected in the 9.0% of tissue samples. Hormone posi- tive status in previously negative tumours was found in 23.0% due to ER, 18.0% due to PgR; appearance of ER and PgR co-expression was noted in 9.0%. Conclusion: The data obtained suggest the need for re-analysis of ster- oid hormone expression in breast tumours after neoadjuvant chemo- therapy in order to correct the treatment guideline. Further investiga- tion of hormone receptor conversion mechanisms may be incorporated into prognostic models for breast cancer and open up additional options for adjuvant therapy. E-PS-02-057 Importance of pathological complete response after neoadjuvant therapy for breast cancer O. Reshetnikova*, L. Rudiuk, A. Musatov, S. Korenev *Immanuel Kant Baltic Federal University, Russia Background & objectives: Breast cancer has a high incidence in women. Assessment of breast tumour response to neoadjuvant chem- otherapy is a key factor in the prognosis of the disease. A complete pathological response (pCR) contributes to a favourable outcome and recurrence-free survival. Methods: Eighty cases of breast cancer (BC) after neoadjuvant chemo- therapy were analysed. The tumour grade was recorded according to the Nottingham Histologic Score. Immunohistochemical (IHC) studies