Targeted massively parallel sequencing of angiosarcomas reveals frequent activation of the mitogen activated protein kinase pathway

Abstract

Angiosarcomas are rare malignant mesenchymal tumors of endothelial differentiation. The clinical behavior is usually aggressive and the prognosis for patients with advanced disease is poor with no effective therapies. The genetic bases of these tumors have been partially revealed in recent studies reporting genetic alterations such as amplifications of MYC (primarily in radiation-associated angiosarcomas), inactivating mutations in PTPRB and R707Q hotspot mutations of PLCG1. Here, we performed a comprehensive genomic analysis of 34 angiosarcomas using a clinically-approved, hybridization-based targeted next-generation sequencing assay for 341 well-established oncogenes and tumor suppressor genes. Over half of the angiosarcomas (n = 18, 53%) harbored genetic alterations affecting the MAPK pathway, involving mutations in KRAS, HRAS, NRAS, BRAF, MAPK1 and NF1, or amplifications in MAPK1/CRKL, CRAF or BRAF. The most frequently detected genetic aberrations were mutations in TP53 in 12 tumors(35%) and losses of CDKN2A in9 tumors (26%). MYC amplifications were generally mutually exclusive of TP53 alterations and CDKN2A loss and were identified in 8 tumors (24%), most of which (n = 7, 88%) arose post-irradiation. Previously reported mutations in PTPRB (n = 10, 29%) and one (3%) PLCG1 R707Q mutation were also identified. Our results demonstrate that angiosarcomas are a genetically heterogeneous group of tumors, harboring a wide range of genetic alterations. The high frequency of genetic events affecting the MAPK pathway suggests that targeted therapies inhibiting MAPK signaling may be promising therapeutic avenues in patients with advanced angiosarcomas.

Keywords: MAPK pathway; MYC; angiosarcoma; genetics.

Figure 1. Distribution of genetic alterations in angiosarcomas

The gene alterations identified in the 34 tumors analyzed are demonstrated in the bar graph. The y-axis depicts the amount of tumor samples harboring the alterations. Loss-of-function (deletion, nonsense single nucleotide variations (SNV) and frameshift mutations or indels) alterations are shown in blue, amplifications in red, and missense SNV or in-frame indels (insertions or deletions) in green.

Figure 2. Co-occurence of mutations in angiosarcoma samples

Recurrently mutated genes are shown on the y-axis and the samples (patients) on the x-axis. Loss-of-function mutations (missense, frame-shift, deletion) are shown in blue, amplifications in red, missense/in frame indels (insertions or deletions) in green and the hotspot PLCG1 R707Q mutation in orange.

Figure 3. Genetic alterations in angiosarcomas affecting the MAPK pathway

Loss-of-function mutations (missense, frame-shift, deletion) are shown in blue, amplifications in red, activating mutations in orange.

Figure 4. DNA copy number alterations in angiosarcomas

Penetration blots of 32 angiosarcomas included in the study (two cases removed due to lower coverage). A fold change value of < −1.5 was applied as a cut off for recognizing a loss and > 1.5 for recognizing a gain. Gains are shown in blue, losses in red. The most frequent gains include MYC on Chr. 8, the most frequent losses CDKN2A on Chr. 9.

Figure 5. Copy number profiles according to MYC status

Penetration blots of the samples included in the study grouped according to MYC status. A. penetration blot of tumors samples with a MYC-amplification. B. penetrations blot of tumors lacking a MYC-amplification. A fold change value of < −1.5 was applied as a cut-off for recognizing a loss and > 1.5 for recognizing a gain. Gains are shown in blue, losses in red.