Abstract LB140: The genomic landscape of primary and secondary angiosarcomas, a rare heterogenous group of soft tissue sarcomas

Background: Angiosarcomas (AS) are a rare heterogenous group of soft tissue sarcomas (STS) that form in the lining of blood vessels or lymphatic vessels. They comprise of primary (de novo) AS and secondary AS. The etiology of primary AS is unknown. Secondary AS arise due to DNA damaging factors like prior radiotherapy (RT), ultraviolet (UV) light exposure or chronic lymphedema (Stewart Treves syndrome). Treatment options are limited and their prognosis is poor. Development of new treatment strategies is difficult due to the rarity of these subgroups of STS. Genomic profiling of primary and secondary AS may provide a rationale for targeted treatment strategies.

Method: Tumor samples were retrospectively collected from patients diagnosed with AS in the Netherlands. Patients were categorized as primary/secondary AS. Genomic profiles were analyzed using “TruSight Oncology 500”, a Next Generation Sequencing panel that analyzes variants in 523 cancer relevant genes.

Results: Tumor DNA from 51 treatment naive AS patients was analyzed. The cohort comprised of 26 patients with a primary AS, divided in 5 subgroups: Heart (n=5, 10%), primary breast (n=5, 10%), skin not UV associated (n=4, 8%), soft tissue (n=5, 10%) and visceral (n=7, 14%) AS. The other 25 patients had a secondary AS, subdivided in RT-associated (n=13, 25%), Stewart Treves (n=5, 10%) and UV-associated (n=7, 14%) AS. Mean Tumor Mutational Burden (TMB) was 7.1 mutations per Mb for all patients (4.2 mut/Mb in primary AS vs 10.1 in secondary AS, p = 0.91). High TMB (≥10 mut/Mb) was found in 6 patients (12%) divided over 3 subgroups: UV associated AS (n=3/7 (43%)), visceral AS (n=2/7 (28%)) and skin not UV associated AS (n=1/4 (25%)). No patients were microsatellite instable. A pathogenic mutation, amplification or deletion was identified in 82% of all patients (n=42, 70% of primary AS vs 100% of secondary AS (p=<0.01)). In 36 patients (71%) at least one (likely) pathogenic mutation was detected (54% primary vs 88% secondary AS, (p=0,013)). In 20 patients (39%) a mutation in the DNA damage response (DDR) pathway was detected (12% primary vs 68% secondary AS (p=<0.01)). The most frequently found mutations were TP53 (10%), BRAF (6%), ERCC4 (6%), PTPRD (6%), WETD2 (6%), SETD2 (6%) and PIK3CA (4%). Amplifications were found in 49% (n=25) of all patients (15% primary vs 84% secondary AS, (p=<0,01)). MYC amplifications were detected in 41% of all patients (15% of primary vs 68% of secondary AS), including 100% of Stewart Treves AS, 92% of RT associated AS and 75% of skin not UV associated AS. FLT4 (20%) and CRKL (12%) amplifications occurred only in secondary AS. FLT4 was seen in 31% of RT-associated AS.

Conclusion: We showed a clear distinction in genomic profiles of AS subgroups with specific pathogenic alterations. Especially secondary AS may benefit from treatment with ICI based on frequent MYC amplifications, DDR mutations, and high TMB. These data show clear evidence for the development of future treatment strategies with targeted therapy and ICI for this rare heterogeneous group of STS.

Citation Format: Stefan G. van Ravensteijn, Yvonne M. Versleijen-Jonkers, Melissa H. Hillebrandt-Roeffen, Maikel Nederkoorn, Mark A. Gorris, Kiek Verrijp, Leonie I. Kroeze, Tessa J. de Bitter, Richarda M. de Voer, Uta E. Flucke, Ingrid M. Desar. The genomic landscape of primary and secondary angiosarcomas, a rare heterogenous group of soft tissue sarcomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB140.

Kaposiform hemangioendothelioma and tufted angioma - (epi)genetic analysis including genome-wide methylation profiling

Kaposiform hemangioendothelioma (KHE) is a locally aggressive vascular condition of childhood and is clinicopathologically related to tufted angioma (TA), a benign skin lesion. Due to their rarity molecular data are scarce. We investigated 7 KHE and 3 TA by comprehensive mutational analysis and genome-wide methylation profiling and compared the clustering, also with vascular malformations. Lesions were from 7 females and 3 males. The age range was 2 months to 9 years with a median of 10 months. KHEs arose in the soft tissue of the thigh (n = 2), retroperitoneum (n = 1), thoracal/abdominal (n = 1), supraclavicular (n = 1) and neck (n = 1). One patient presented with multiple lesions without further information. Two patients developed a Kasabach-Merritt phenomenon. TAs originated in the skin of the shoulder (n = 2) and nose/forehead (n = 1). Of the 5 KHEs and 2 TAs investigated by DNA sequencing, one TA showed a hot spot mutation in NRAS, and one KHE a mutation in RAD50. Unsupervised hierarchical clustering analysis indicated a common methylation pattern of KHEs and TAs, which separated from the homogeneous methylation pattern of vascular malformations. In conclusion, methylation profiling provides further evidence for KHEs and TAs potentially forming a spectrum of one entity. Using next generation sequencing, heterogeneous mutations were found in a subset of cases (2/7) without the presence of GNA14 mutations, previously reported in KHE and TA.