angiosarcoma

n. (Medicine) rare and rapidly growing malignant tumour that begins in a blood vessel or in lymph vessels

Hemangiosarcoma is a rare, rapidly growing, highly invasive variety of cancer. It is a blood-fed sarcoma; that is, blood vessels grow directly into the tumor and it is typically filled with blood. A frequent cause of death is the rupturing of this tumor, causing the victim to rapidly bleed to death.
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Angiosarcoma /an·gio·sar·co·ma/ a malignant neoplasm arising from vascular endothelial cells; the term may be used generally or may denote a [more]Angiosarcoma - Community and Resources

Noun
1. a rare malignant neoplasm arising from vascular tissue; usually occurs in the breast and skin and is believed to originate from the endothelial cells of blood vessels
(hypernym) malignant tumor, malignant neoplasm, metastatic tumor

noun
malignant tumour in a blood vessel