ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 Results: Overexpression of at least one immune checkpoint was found in 95.2% of samples. CTLA-4 was overexpressed mostly in Triple-Negative/Basal-like phenotypes (p=0.046), whereas PDCD1 and CD276 were more frequently found in Luminal tumours (all p<0.023). CD274 and PDCD1LG2 showed no correlation with immunophenotype. High CTLA-4, PDCD1, CD274 and PDCD1LG2 expression was associated with a mid- dle/high proliferation rate (all p<0.039), and presence of TILs (all p<0.011), with opposite results for CD276 (p=0.048, and 0.026, respectively). CTLA-4 overexpression correlated with better disease-free survival -DFS- (p=0.037), and specifically among HER2-enriched subtype (DFS p=0.033, and overall sur- vival p=0.011). Conclusion: Our data support that CTLA-4, PDCD1, CD274, and PDCD1LG2 are potential biomarkers of BC aggressiveness. Para- doxically, CTLA-4 stratified a subgroup of HER2-enriched patients with a better outcome. Supported by Grants ISABIAL (NR-180202, UGP-18-231, UGP- 19-291, UGP-20-090) PS-01-016 The malignancy of benignancy. The malignant consequences of benign breast tumours. Is the onus on pathologists? Post- pregnancy associated infarcted fibroadenoma, a rapidly grow- ing benign phyllodes tumour, a benign phyllodes tumour in an adolescent girl S. Di Palma*, A. Gamage, P. Partlett, F. Pakzad, E. Rakha, E. Clayton *Royal Surrey County Hospital, United Kingdom Background & objectives: Fibro-epithelial lesions of the breast can be difficult to assess, especially when dealing with core biop- sies. In uncommon clinical settings such as pregnancy, young girls or a size that would require mastectomy, they are even more dif- ficult to assess. Methods: Here we report on three cases of fibroepithelial lesions, where caring clinicians were concerned about malignancy despite benign pathology reports. We discuss the difficulties of making clinicians accept a benign pathology diagnosis despite the wor- rying clinical presentation. Literature for similar cases confirmed that these are rare but well-known conditions usually described in single or very small series case reports. Results: In one case, the core biopsy was reported as B2, fibroad- enoma with necrosis. Despite a benign report, diagnostic surgical excision was performed. Following MDT, it was revealed that the patient was post-partum and lactating. Patient 2 had a B3 core biopsy for a spindle cells tumour, occupying most of the breast. Excision biopsy was unwelcome because the size would have required a mastectomy, not consistent with a B3 report. Additional biopsies revealing an epithelial component consistent with phyl- lodes tumour were required for diagnosis. Patient 3 was a 17-year- old girl with a 70mm lump in her breast. Clinical concern led to surgical resection without prior core biopsy revealing benign phyllodes tumour. Conclusion: Benign fibroepithelial tumours simulating malig- nancy on clinical presentation are well known to pathologists but still create uncertainty in clinicians. Although rare, in one year we have encountered and correctly identified three such cases. Our experience, where clinicians are not prepared to accept a diagnosis of benign/uncertain tumour on core biop- sies, suggests that more education of these tumour subtypes is essential if clinicians are to accept our diagnosis and organize patient management accordingly. PS-01-018 Breast interstitium or "Hartveit’s Labyrinth": morphology and relationship to disease processes S. Gordin*, B. Belovarac, A. Serrano, L. Chiriboga, B. Zeck, F. Darvishian, D. Nimeh, U. Ozerdem, S. Badve, R. Wells, N. Theise *NYU Langone Medical Center, New York, NY, USA Background & objectives: The breast stroma contains intersti- tial spaces (IS) supported by collagen bundles and intermittently lined by CD34+/vimentin+ interstitial lining cells (ILC) identified previously by Hartveit (Histopathology, 1990) as pre-lymphatic "labyrinth." Current study investigates morphology and role of interstitium in disease processes. Methods: Normal breast tissue with skin and breast tissue with PASH were stained for HA with peroxidase labelled HABP (hya- luronic acid binding protein) to investigate continuity between intralobular/interlobular and skin IS. IHC multiplex co-staining for CD34 and vimentin was used to demonstrate spatial relationship of the interstitial HA with ILC (Discovery Ultra, Ventana) and IHC for Galectin/Vimentin and p63/Vimentin in PASH. Results: HABP staining showed HA throughout the IS of the normal breast sections and demonstrated continuity of IS between intralobular, interlobular, perivascular and perineu- ral interstitium. In samples with PASH, HABP showed expan- sion of IS associated with thickened collagen bundles. IHC for p16/Vimentin showed significantly increased staining in PASH comparing to normal breast tissue and Galectin/Vimentin demonstrated positive Galectin staining along cell membrane of some fibroblasts in PASH. Conclusion: Breast IS form a continuous space permeating all stromal compartments: periductal, interlobular, nipple, and dermis. Additionally, IS are continuous between breast stroma and perivascular adventitia and perineurium, connections to a body-wide system of IS. Our data support that PASH is a keloid- type expansion and remodelling of the mammary IS, which further suggests that mammary interstitium may play roles in fibrocystic disease, gynecomastia and malignant states such as invasive lobular carcinoma and could provide a route to spread via lymphatics/ perineural routes. PS-01-019 The effect of neoadjuvant chemotherapy on histologic grade and hormone receptor status in HER2/Neu-negative Luminal-B tumours of the breast O.C. Eren*, S.E. Horoz, N. Arı, G. Menetlioglu, H. Kaya *Marmara University, Turkey Background & objectives: With stratification of tumours, neoadjuvant chemotherapy (NACT) has become more common in Her2/Neu-negative Luminal-B group. Here we investigate the effect of NACT on histologic grade/hormone receptor (HR) status and tumour representation adequacy in pre-NACT core biopsies. Methods: Her2/Neu-negative luminal-B cases between 2017 and 2020 with available core biopsy and post-NACT resection slides were retrieved. Hospital records, original sign-out reports and glass slides were retrospectively reviewed for demographic data, pre-/ post-NACT histologic grade and HR status of tumours, as well as number of pre-NACT core biopsy pieces available for tumoral representation. Results: 45 cases were identified, with a mean age of 49.8. In the pre-NACT core biopsy samples, average number of pieces and percentage of tumoral tissue in the pieces were 3.82 and 52% respectively. 40% (n=18) of cases were attributed a histologic grade different from what had been originally assigned to them with the core biopsy, while 4.4% of cases S65