ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 architecture. Our patient was in clinical staging cT3N0M0 and was qualified for postoperative radiotherapy (total dose 54/60Gy). Conclusion: In conclusion, BOS is an exceptional diagnosis and up-to-date, only a few cases have been reported. The differential diagnosis with MC (if lacking invasive/in-situ carcinoma the immunohistochemical confirmation of epithelial differentiation is needed) and MTP requires extended sampling and immunohistochemical assessment. Treatment should include complete surgical removal of the tumour with R0 margins; adjuvant chemotherapy (methotrexate and bleomycin, cyclophosphamide, CDDP, doxorubicin, and ifosfamide) seems to be effective, however, no standard regimen has been established for extraskeletal osteosarcoma yet. E-PS-02-030 Heterogeneity of breast cancer surrogate subtype of primary tumour and local metastases K. Konyshev*, S. Sazonov *Institute of Medical Cell Technologies, Ural State Medical Uni- versity, Russia Background & objectives: Patterns of surrogate subtype change in breast cancer (BC) metastases stay unclear. This heterogeneity may be the reason of treatment effect decrease. Objective: to describe changes of surrogate subtype of breast cancer in regional metastases compared with primary tumour (PT). Methods: Postoperative specimens of primary and metastatic tumours taken from 104 patients were examined using immunohis- tochemistry (ER, PR, Her2/neu, Ki67) and SISH (HER2). Allred, ASCO/CAP 2013 and percentage of stained tumour cell nuclei sys- tems were used. Surrogate subtypes of primary tumour and metas- tasis were assessed according to St Gallen 2015 recommendations. Frequencies of subtype change in BC metastasizing were analysed. Results: Primary tumour and metastasis subtypes were the same in 73 cases (70,2%, 95% CI 60,3-78,6%), discordant in 31 cases (29,8%, 95% CI 21,4-39,7%) (p<0,05, Fischer’s exact probability test). Among 52 cases with PT luminal A subtype metastasis had another subtype in 10 cases (19,2%, 95% CI 10,1-33,0%); among 16 cases with luminal B subtype – in 11 cases (68,7%, 95% CI 41,5-87,9%); among 8 cases with HR+ Her2+ subtype – in 3 cases (37,5%, 95% CI 10,2-74,1%); among 8 cases with HR- Her2+ subtype – in 4 cases (50,0%, 95% CI 17,4-82,6%); among 20 cases with triple negative subtype – in 3 cases (15,0%, 95% CI 4,0-38,9%). Conclusion: Breast cancer primary and metastatic tumour surrogate subtype is concordant in the majority of cases in the whole sample. Subtype heterogeneity of metastatic and primary tumour has the highest frequency among cases with luminal B primary tumour subtype. Triple negative subtype is the most stable during regional metastasizing of breast cancer. E-PS-02-031 Two cases for a rare association; mixed tumour of the breast which contains acinic cell carcinoma and metaplastic carci- noma components K.E. Akar*, İ. Hotmanoğlu Şahin, H. Toper, H. Kaya *Marmara University Pendik Training and Research Hospital Department of Pathology, Istanbul, Turkey Background & objectives: Acinic cell carcinoma is a rare form of salivary gland-type breast cancer that shows indolent behaviour, in contrast to other triple-negative cancers. Metaplastic carcinoma is a term for breast cancers characterized by neoplastic cells differentiating into squamous or mesenchymal-looking components. Methods: Case 1: 42 years-old female patient presented with a mass in the right breast. Trucut biopsy revealed metaplastic car- cinoma. After chemotherapy, she underwent nipple sparing mas- tectomy. In the resected specimen, tumour characterized by two distinct components was observed. In the one component, tumour was growing in infiltrative pattern with small acinar structures. Case 2: 83 years-old female patient presented with a mass in the right breast. Trucut biopsy specimen revealed invasive carcinoma characterized by acinar structures. Tumour cells were characterized with granular and eosinophilic cytoplasm some of which contain zymogen granules. Results: Tumour cells were characterized with monotonous round cells with granular and eosinophilic cytoplasm some of which contain zymogen granules. Immunohistochemically, neoplastic cells were positive for lysozyme and S100. In the other component, pleomorphic and discohesive tumour cells scattered in chondromyxoid matrix was observed. The case was reported as metaplastic carcinoma with acinic cell carcinoma. In NGS TP53(c.818G>A) and KRAS(c.351A>C) mutations were observed. Immunohistochemically, neoplastic cells were positive for lysozyme, antichymotrypsin and S100. The case was reported as acinic cell carcinoma. In the resected specimen, acinic cell carcinoma was accompanied by large areas of metaplastic carcinoma with discohesive cells. In NGS TP53(c.488A>G) and PTEN(c.166_167del) mutations were observed. Conclusion: Acinic cell carcinomas are usually seen in pure form, but in rare cases, they may be associated with high-grade triple-negative carcinoma component, such as metaplastic carcinoma. E-PS-02-032 A relapsing breast abscess – about a case S. Antunes*, C. Dahlstedt Ferreira, R. Rosas, C. Pereira *Hospital Garcia de Orta, Portugal Background & objectives: Cystic neutrophilic granulomatous mastitis (CNGM) is a rare subtype of granulomatous mastitis with a highly distinct histological pattern often associated with Corynebacterium species, although evidence of corynebacterial infection can be diffi- cult to prove. Methods: A parous 29-year-old woman, an immigrant from Nepal living in Portugal for a year, presented in the emergency department with a painful tumefaction in right breast. Radiological investigation revealed an abscess and she was discharged with antibiotic therapy. Three days later she was submitted to abscess drainage and Corynebacterium species were isolated. During follow-up, a core needle biopsy was performed. Results: Microscopically, the biopsy revealed breast parenchyma with an exuberant chronic granulomatous process, constituted by an inflammatory infiltrate of lymphocytes, plasma cells, neu- trophils, Langhans giant multinucleated cells, and well-formed granulomas with occasional central cystic spaces surrounded by neutrophils. In Gram stain rare bacillary structures were observed. PAS, Grocott and Ziehl-Neelsen were negative. Due to the relapsing nature of the abscess, she completed several antibiotic cycles and was posteriorly started on corticosteroids. Currently, she is asymptomatic. Conclusion: The diagnosis of CNGM is often missed or delayed due to its rarity and many potential mimickers. Invasive carcinoma is the most important entity to consider in differential diagnosis, as both clinical presentation and radiological features can mimic S199