(P 056) PROGNOSTIC VALUE OF VESSELS ENCAPSULATING TUMOR CLUSTERS (VETC) IN SARCOMA.

Objective: How sarcoma metastasize is unknown. VETC has been described as an epithelial-to-mesenchymal-transition independent process of metastasis: endothelium covers neoplastic clusters allowing tumor dissemination. It has also been shown to be a predictive of tyrosine kinase inhibitors (TKI) response. The objectives of the present study are: 1) to assess the presence of VETC in sarcoma; 2) to model its prognostic role.

Methods: The study was retrospective. We selected 54 cases of sarcomas (6 dedifferentiated liposarcoma – DDLPS–, 10 gastrointestinal stromal tumors –GIST–, 6 retroperitoneal leiomyosarcomas –LMS–, 9 myxoid-liposarcomas –MLPS–, 8 malignant peripheral nerve sheath tumors –MPNST–, 10 solitary fibrous tumors – SFT– , 5 undifferentiated pleomorphic sarcomas –UPS–); of them 31 were metastatic (M1 group), 23 were not (M0 group, defined as least 5 years of negative follow-up). High risk GIST and SFT, and grade 3 FNCLCC were considered high grade. VETC was assessed with CD31 immunohistochemistry and defined as a continuous endothelial lining around tumor clusters. We used Bayesian probabilistic modeling to detect small effects and multilevel hierarchical modeling to reduce overfitting. Models were fit using Stan and R. CI were computed with the HPDI method for 89%. The whole posterior probability (PP) was used for calculations.

Results: The two groups (M0 & M1) were substantially homogeneous: the CI of the contrast PP (CPP) included 0 in each histology for sex, age, size, and grade; VETC was more expressed in M1 SFT cases with almost all the CPP mass above the 0. Also, UPS and GIST showed VETC to be more present in metastatic diseases with 79% and 78% respectively of the CPP mass above 0 (see table). Metastasis free survival (MFS) analysis showed that VETC in SFT and UPS with a coefficient of 2.42 (CI 0.73 – 4.65) and 1.94 (CI 0.16 – 3.67); for the latter the median was reached with a PP density of median MFS of 65 months (mo) (standard deviation, SD: 74 mo) for VETC- Vs 11 mo (SD: 14 mo) for VETC+. Similarly, disease specific survival analysis showed – in SFT and UPS – that VETC was negatively associated with prognosis with coefficients of 1.24 and 2.34; however the CI covered slightly the 0 (-0.54 – 3.96 and -0.09 – 5.73, respectively).

Conclusion: We found VETC in sarcoma and highlighted its prognostic role in SFT and UPS.

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Table1_VETC_SA.xlsx