ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 Background & objectives: Osteosarcoma is the most common primary malignant bone tumour in children and young adults. Not much work has been done to explore immunotherapy targeting PD1-PDL1 axis in osteosarcoma. This study shows correlation between PDL1 expression and TILs in high-grade osteosarcoma. Methods: PDL1 expression by immunohistochemistry and TILs were evaluated in 40 resection specimens of high-grade osteosarcoma. A score of 0-3 was given for PDL1 expression. TILs were calculated under 400X (in 10 fields) and a score of 0-3 was given based on intensity. Clinical data was collected from record section. Results: The mean age of presentation was 16 years with male to female ratio 1.6:1. The most common bone involved was femur followed by tibia. The most common site of metastasis was lung. PDL1 was positive in 82.5% cases (33/40). 17.5% (7/40) did not show PDL1 expression. 15% (6/40) showed a score of +1, 27.5% a score of +2 and 40% (16/40) a score of +3. It was observed that PDL1 expression correlated with TILs scoring (p=0.029). How- ever, PDL1 expression and TILs did not correlate with any param- eter like age; sex; histologic type; tumour size, site and necrosis; metastasis; progression and relapse; duration of chemotherapy; radiotherapy; follow up and survival data. Conclusion: Our research shows that PDL1 is an independent marker in high-grade osteosarcoma and cannot be taken as a basis for judging progression of the disease. However, since in our study it correlated directly with the TILs density, it can be regarded as a potential therapeutic target for tumour immunotherapy. OFP-04-006 Osteoblastoma-like osteosarcoma: a case series and literature review S. Sevim*, E. Gedik, S. Yuksel, M.O. Karaca, H.Y. Yildiz, G. Kaygusuz *Ankara University Medical School, Pathology Department, Turkey Background & objectives: Osteosarcoma (OS) is the most com- mon primary bone tumour in young adults and children. Osteoblas- toma-like osteosarcoma (OBLOS) is a rare subtype that accounts approximately 1% of all OSs. In this study, we present three cases of OBLOS with clinicopathological correlation. Methods: Gross materials were fixed with 10% buffered forma- lin. After decalcification process, hematoxylin and eosin (H&E) sections of 4-5 microns were obtained. The cases (n=3) were ana- lysed according to their histopathological, radiological and clini- cal features. In one case (talus localized lesion), beta-catenin was performed immunohistochemically. Results: Two of the three cases were male and one female, and the mean age was 43.33 years. The tumours were located in the iliac bone, 4th finger of the hand, and talus. The cross-sectional surface of the tumours was solid and heterogeneous, and haemorrhagic areas were also observed. The tumours had infiltrative borders and were composed of oval-spindle shaped cells with vesicular nuclei and eosinophilic cytoplasm. Osteoclastic giant cells and mitoses were observed. Nuclear beta-catenin staining was not observed in the talus localized lesion. Two patients had a history of neoadju- vant therapy and, the other patient died due to lung metastasis. Conclusion: Two histological features are helpful in differential diagnosis of osteoblastoma, OBLOS. Permeation around host bone and loss of peripheral maturation of the lesion favours OBLOS, whereas osteoblastoma is well-defined and there is peripheral maturation. These lesions may be radiolucent/radiodense, and OBLOS can contain features of osteoblastoma and OS. Some studies revealed that COX2, FOS, beta-catenin immunoprofile dif- fers between osteoblastoma-OBLOS. We consider that excisional biopsy is important to support this distinction, especially if radio- logical findings cannot rule out or support malignancy. OFP-04-007 Prognostic value of vessels encapsulating tumour clusters (VETC) in sarcoma S.L. Renne*, M. Tassan-Mangina, I. Santori, L. Ruspi, F. Sicoli, P. Colombo, M. Cammelli, V. Quagliuolo, L. Terracciano, L. Di Tommaso, F. Cananzi *Humanitas Clinical and Research Center – IRCCS, Humanitas University, Department of Biomedical Sciences, Rozzano, Italy Background & objectives: How sarcoma metastasize is unknown. VETC has been described as an epithelial-to-mesenchymal-tran- sition independent process of metastasis: endothelium covers neo- plastic clusters allowing tumour dissemination. Our aims are to assess the presence of VETC in sarcoma, and to model its prog- nostic role. Methods: The study was retrospective. We selected 54 cases of sarcomas (6_DDLPS, 10_GIST, 6_LMS, 9_MLPS, 8_MPNST, 10_ SFT, 5_UPS); of them 31 were metastatic (M1 group), 23 were not (M0 group, defined as least 5 years of negative follow-up). VETC was assessed with CD31 immunohistochemistry and defined as a continuous endothelial lining around tumour clusters. We used probabilistic modelling for the analysis. Results: Within each histology, the two groups (M0 & M1) were substantially homogeneous: most (89%CI) of posterior probability(PP) difference –i.e. the contrast CPP– included 0 for sex, age, size, and grade. VETC in SFT was basically only expressed in M1, with almost all the CPP mass above the 0. Also, in UPS and GIST, VETC was more probable to be in metastatic diseases with 79% and 78% respectively of the CPP mass above 0. VETC was prognostic of metastasis free survival in SFT and UPS with a coefficient of 2.42(CI_0.73–4.65) and 1.94(CI_0.16–3.67); only UPS reached median survival of 65 months(mo)(standard deviation, SD:74_mo) for VETC- Vs 11 mo (SD:14_mo) for VETC+. Conclusion: VETC was present in all the investigated histotypes but two (MLPS, MPNST). VETC was prognostic of disease free survival in UPS and SFT. These findings warrants confirmations on a larger series. Moreover, in some carcinomas VETC has been shown to be predic- tive of tyrosine-kinase-inhibitors (TKI) response; our results prompt us to to verify if this is also true for SFT, where TKI are often used in clinical practice. OFP-04-008 Immunohistochemical expression of H3.3G34W in 67 giant cell tumours of bone and its diagnostic mimics: a single institutional study at a tertiary cancer referral centre in India B. Rekhi*, V. Dave, S. Keltle, O. Shetty, A. Puri *Department of Surgical Pathology/Tata Memorial Hospital, Parel, Mumbai, India Background & objectives: Despite its classic histopathological features, sometimes there is a challenge in differentiating giant cell tumour of bone(GCTB) from its various mimics. Lately, Histone 3.3G34W has been identified as a useful immunohistochemical marker. To evaluate H3.3G34W immunohistochemical staining in 67 GCTBs. Methods: Immunohistochemical staining for H3.3G34W (monoclonal, RM263, 1:100 dilution) was graded in terms of staining intensity(1+to 3+) and the percentage of tumour cells showing crisp nuclear staining. Seventy-one(65.7 %) GCTBs S16