ECP 2023 Abstracts

S34 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 EPClin towards a LR, with only 13% of pN+ cases. Ki67 index was ≥20% in 67% of cases. Conclusion: In G1 HR breast cancer, despite the presence of poor clinico- pathological features, most tumours already have a high genomic profile (proliferation genes of EP index). Therefore, Ki67 index is a poor predictor of the genomic profile of the tumour in these cases. Conversely, G3 LR identifies a subset of tumours with high expression of proliferation genes. In these cases, favourable clinicopathological features often modify the EPClin index. Here, the Ki67 index is a more reliable marker of the genomic profile. OFP-09-003 Intraoperative evaluation of sentinel lymph nodes after neoadju- vant therapy in breast cancer patients has low accuracy rate due to unique challenges S. Sahoo*, M. Huerta-Rosario, R. Zhang, Y. Fang *UT Southwestern Medical Center, USA Background & objectives: Intraoperative evaluation (IOE) of sentinel lymph nodes (SLNs) to detect metastases in breast cancer patients after neoadjuvant therapy is challenging due to therapy related changes. The objective of the study is to determine the accuracy of IOE of SLNs. Methods: This retrospective study included a total of 1098 SLNs from 294 patients treated between January of 2020 through March of 2023. The intraoperative results (13 patients had touch preps and 281 patients had frozen sections) were compared with the final pathology results. Results: Of the 294 patients, 191 patients had negative results and 103 had positive results on IOE. Of the 191 patients with negative results, 32 had false negative results. Of the 32 false negative cases, 10 were macro- metastases, 19 were micrometastases and 3 were isolated tumour cells. There were no false positive results. The overall sensitivity, specificity, positive predictive value and negative predictive value are 76.3%, 100%, 100% and 83.2%, respectively. The sensitivity rate for detecting macro- metastasis was higher (89.9%) than micro-metastasis (38.9%). Conclusion: The sensitivity of detecting metastasis intra-operatively is lower after neoadjuvant systemic therapy (NST). Our results of high false negative rates in detecting micro-metastasis is consistent with previous stud- ies. The major reason of missing metastasis (including macro-metastasis) is due to partial response to therapy where residual tumour cells scattered in a larger fibro-inflammatory background are difficult to recognize. Therefore, it may not be possible to attain the same level of sensitivity in the NST set- ting when compared with primary surgery setting. OFP-09-004 TRPS1 is a highly sensitive marker for breast cancer: a tissue micro- array study evaluating more than 19,000 tumours from 152 different tumour entities M. Lennartz*, N. Blessin, C. Hube-Magg, T. Krech, A. Hinsch, E. Burandt, G. Sauter, R. Simon, P. Lebok, D. Dum, S. Minner, F. Jacob- sen, T.S. Clauditz, C. Bernreuther, S. Steurer *University Medical Center Hamburg-Eppendorf, Germany Background & objectives: TRPS1 (Trichorhinophalangeal syndrome 1) is a nuclear protein expressed in breast epithelial cells. TRPS1 immunohis- tochemistry (IHC) has thus been suggested as a marker for breast cancer. However, reports on TRPS1 positivity in other cancer types are piling up. Methods: To comprehensively determine the diagnostic utility of TRPS1 IHC, tissue microarrays containing 19,201 samples from 152 different tumour types and subtypes were analysed. GATA3 IHC data were avail- able from 11,891 of these tumours from a previous study. Results: TRPS1 positivity occurred in 86 of 152 tumour categories of which 36 contained at least one strongly positive case. TRPS1 staining predominated in various types of breast carcinomas (51%-100%) and was also seen in various subtypes of soft tissue tumours (up to 100%), salivary gland tumours (up to 46%), squamous cell carcinomas (up to 35%), and gynaecological cancers (up to 40%) as well as in other tumours. TRPS1 positivity occurred in only 1.8% of 1,083 urothelial neoplasms. Positivity for both TRPS1 and GATA3 occurred in 47.4%-100% of breast cancers, up to 30% of salivary gland tumours, but in only 29 (0.3%) of 9,835 tumours from 134 other cancer entities. Conclusion: Although TRPS1 expression can be seen in many differ- ent tumour types, TRPS1 Immunohistochemistry has high utility for the identification of cancers of breast or salivary gland origin, especially in combination with GATA3. The virtual absence of TRPS1 positivity in urothelial neoplasms is useful for the distinction of GATA3 positive urothelial carcinoma from breast cancer. OFP-09-005 Risk stratification in invasive lobular carcinoma of the breast by clinicopathological features and Prosigna-PAM50 multigene assay characterisation J. Vaz Silva*, A. Varelas, C. Escudeiro, M.R. Teixeira, C. Leal, N. Coimbra *Pathology Department, Portuguese Oncology Institute of Porto (IPO- Porto), Porto, School of Medicine, University of Minho, Braga, Portugal Background & objectives: Invasive lobular carcinoma(ILC), the second most common type of invasive breast carcinoma(IBC), is reported to have good short-term prognosis. However, several studies demonstrate that long-term outcome is similar or worse than IBC-NST, hindering thera- peutic decision in early and intermediate-risk tumours. Methods: Prosigna-PAM50, a multigene assay that encompasses tumour size and nodal metastasis, determines intrinsic subtype and risk of recurrence(ROR), assigning a probability for 10-year distant recurrence(ROR10). In our institution, selected patients with inter- mediate risk criteria undergo Prosigna-PAM50 characterization to aid therapeutic decision. Here, we compared Prosigna-PAM50 ROR results with different clinicopathological characteristics of patients diagnosed with ILC, thus characterizing this population. Results: Tumours were <2cm in 49(52%) cases and node metasta- ses (LNM) were present in 22(23%). All were ER-positive and HER- 2-negative. PR expression was negative/low(<20%) in 22(23%). Ki-67 proliferation-index(Ki-67) was >15% in 28(30%). Prosigna-PAM50 classified 85(89%) as Luminal-A and 10(11%) as Luminal-B. Overall ROR10 average was 7,25%, with 55(58%) classi- fied as low-ROR, 34(36%) as intermediate-ROR and 6(6%) as high-ROR. Low-ROR tumours were >2cm in 23(41,8%), LNM were present in 4(7,4%), and Ki-67 was >15% in 11(20%) cases. Intermediate-ROR tumours were >2cm in 18(52,9%), LNM present in 11(32,4%), while Ki-67 was >15% in 13(44,8%) cases. High-ROR tumours were >2cm in 5(83,3%) case, LNM present in 4(66,7%), while Ki-67 was >15% in 4(66,7%) cases. Conclusion: Despite ILC being associated with favourable prognostic features, there is still ongoing debate regarding its long-term outcome, making risk stratification and therapeutic decision difficult. Many cases demonstrated overlap between clinicopathological risk assessment and Prosigna-PAM50 characterization. However, Prosigna- PAM50 provides additional risk discrimination, for example in cases with LNM but low-ROR. Although multigene risk assays are validated for IBC, extended clinical follow-up will be essential to further refine their prognostic value and clinical application in the setting of ILC. OFP-09-006 Dako HercepTest (poly) allocates more cases to HER2-low group compared to ventana PATHWAY 4B5 anti-HER2 assay: a multi- centre study on 116 invasive breast cancer cases O.C. Eren*, O.C. Taskin, M. Oktay, A. Baygul, F. Aktepe, N. Kapucuoglu *Koç University Hospital, Department of Pathology, Turkey Background & objectives: Treatment of breast cancer revolves around HER2 protein, via targeted antibodies or antibody-drug conjugates. As