<b><i>Introduction:</i></b> Angiosarcoma (AS) is a rare subtype of soft tissue sarcoma. We performed a retrospective analysis of patient characteristics, treatments and prognostic factors in patients treated in a single sarcoma center. <b><i>Methods:</i></b> We reviewed records of patients treated between 1987 and 2018, categorized in 7 different subtypes according to tissue of origin and underlying risk factors. The Kaplan-Meier method was used to estimate overall survival (OS); the Cox proportional hazards model was used to study prognostic variables. <b><i>Results:</i></b> Among 134 patients, 30% had radiation-induced, 31% primary soft tissue, 24% cutaneous, 5% breast, 4% bone, 2% lymphedema-associated and 4% unknown primary AS. Key patient/disease characteristics varied between subgroups. The median OS was 22.0 months for the entire cohort, with 28.9% with a 5-year survival. Metastasis at diagnosis was seen in 23% of patients; 38% developed metachronous metastasis. Sixty-six (49%) patients received systemic therapy; common first-line treatments were doxorubicin (48%) and paclitaxel (39%), without a significant difference in OS between agents. Younger age, breast/radiation-induced AS, primary surgery and palliative chemotherapy were associated with better OS. Synchronous metastasis, soft tissue/unknown primary location correlated with poor survival. <b><i>Conclusion:</i></b> AS is a very heterogeneous sarcoma subtype, with substantial variability in clinical presentation and survival among patient subsets. Prognosis is poor, and there is no difference in outcome comparing the 2 most frequently used chemotherapy agents in the first line, paclitaxel and doxorubicin.

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10530 Background: Germline pathogenic variants (PV) in the tumor suppressor gene TP53 are associated with a high risk of developing diverse malignancies, often at young age, and predispose to Li-Fraumeni syndrome (LFS). Surveillance programs for presymptomatic PV carriers have shown survival benefit in a non-randomized trial. Here we describe the surveillance findings and clinical outcomes of adults with TP53 PV undergoing a standardized screening protocol. Methods: We identified adults with germline PV in TP53 who underwent surveillance at the University Hospitals Leuven, Belgium, between 04/2013 and 08/2020. Patients with prior cancer were allowed, while patients with an active malignancy requiring treatment at diagnosis of the TP53 PV were excluded. Surveillance was performed per modified Toronto protocol, including annual whole body diffusion-weighted MRI (WB-DWI/MRI), brain MRI, abdominal ultrasound (US), endoscopic surveillance, laboratory tests, dermatological examination and breast MRI/US in females. The primary aim was to evaluate the number and type of malignancies and premalignant lesions diagnosed during screening and to assess the proportion of malignancies detected by surveillance. Secondary outcomes were the cancer detection rate during the first year of screening, the proportion of carriers with false-positive findings, and overall survival. Results: We included 42 adults from 20 apparently unrelated families. Median age was 38y (range, 17-70y) and 23 had a history of prior cancer. After a median follow-up of 41.5mo, we diagnosed 18 cancers in 12/42 participants (29%). Overall survival was 95% in all participants, including 2 carriers who opted to discontinue surveillance. Surveillance detected 10/18 cancers (56%), the majority of whom through WB-DWI/MRI (6/10; 60%). No malignancies were identified with brain MRI. In 5/42 individuals (12%), surveillance detected a malignancy during the first year of screening. Only 2/10 cancers discovered with surveillance (1 soft tissue and 1 bone sarcoma) belong to the LFS core tumors. Cancers not detected with surveillance (8/18) were 6 non-melanoma skin cancers and 2 interval cancers (sarcoma post radiation, secondary acute leukemia). Additionally, we detected 27 premalignant lesions in 11/42 patients (26%), of whom 78% were diagnosed by colonoscopy. False-positive findings occurred in 7/42 patients (17%) and were mostly seen with WB-DWI/MRI. Conclusions: Adults with germline PV in TP53 that undergo surveillance have high cancer detection rates. The majority of malignancies were asymptomatic at diagnosis and detected with WB-DWI/MRI. Despite the high cancer incidence, few LFS core cancers were diagnosed and survival was encouraging. Increased genetic testing changes the clinical picture of germline TP53 carrier populations, justifying the transition from LFS to a wider concept of heritable TP53-related cancer syndrome.